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Difference between revisions of "Hard Disks - The Essential Accessory"

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<pre>
+
A simple observation: the first accessory any computer user
 +
should buy is hard drive. On a dollar for dollar basis nothing
 +
speeds up processing and expands convenience like a hard drive.
 +
The bad news? The substantial storage capacity of a hard drive
 +
contains the seeds of data catastrophe if you don't understand
 +
how to CAREFULLY maintain a hard drive. Some reference
 +
information pertaining to larger desktop hard drives as well as
 +
smaller laptop drives has been retained since drives in both
 +
computers are similar in function although different in form and
 +
size.
  
      ----------------------------------------------------------------
+
Many computer operations tend to slow down at the critical
+
bottleneck of information transfer from computer memory (RAM) to
                    HARD DISKS - THE ESSENTIAL ACCESSORY
+
disk. The faster the transfer, the faster the program operates.
 +
Nine times out of ten it is the bottleneck formed when
 +
information flows to or from a disk that you and your program
 +
must wait. This is where a hard drive really shines - speed.
  
      ----------------------------------------------------------------  
+
Given the best possible treatment, a hard drive should last from
 +
eight to fifteen years. Drive manufacturers typically suggest
 +
30,000 to 70,000 hours of routine life for a hard drive before
 +
failure. If you kept your PC on for a 40 hour work week for 50
 +
weeks - you could expect about 15 years of service for a drive
 +
rated at 30,000 hours. Some hard drive users even suggest
 +
leaving the drive on continuously or alternatively turning it on
 +
in the morning and off at night to minimize motor and bearing
 +
wear since it is the starting shock which wears most heavily on
 +
a drive. However, given marginal treatment or abuse, you can
 +
expect about fifteen minutes of service followed by a $250
 +
repair bill. Obviously a little information about hard drives
 +
and their care can't hurt.
  
      A simple observation: the first accessory any computer user
+
      should buy is hard drive. On a dollar for dollar basis nothing
 
      speeds up processing and expands convenience like a hard drive.
 
      The bad news? The substantial storage capacity of a hard drive
 
      contains the seeds of data catastrophe if you don't understand
 
      how to CAREFULLY maintain a hard drive. Some reference
 
      information pertaining to larger desktop hard drives as well as
 
      smaller laptop drives has been retained since drives in both
 
      computers are similar in function although different in form and
 
      size.
 
 
 
      Many computer operations tend to slow down at the critical
 
      bottleneck of information transfer from computer memory (RAM) to
 
      disk. The faster the transfer, the faster the program operates.
 
      Nine times out of ten it is the bottleneck formed when
 
      information flows to or from a disk that you and your program
 
      must wait. This is where a hard drive really shines - speed.
 
  
      Given the best possible treatment, a hard drive should last from
+
TECHNOLOGY 101 - BOOT CAMP FOR HARD DRIVE USERS
      eight to fifteen years. Drive manufacturers typically suggest
 
      30,000 to 70,000 hours of routine life for a hard drive before
 
      failure. If you kept your PC on for a 40 hour work week for 50
 
      weeks - you could expect about 15 years of service for a drive
 
      rated at 30,000 hours. Some hard drive users even suggest
 
      leaving the drive on continuously or alternatively turning it on
 
      in the morning and off at night to minimize motor and bearing
 
      wear since it is the starting shock which wears most heavily on
 
      a drive. However, given marginal treatment or abuse, you can
 
      expect about fifteen minutes of service followed by a $250
 
      repair bill. Obviously a little information about hard drives
 
      and their care can't hurt.
 
  
      ----------------------------------------------------------------
 
 
                TECHNOLOGY 101 - BOOT CAMP FOR HARD DRIVE USERS
 
  
      ----------------------------------------------------------------  
+
What is a hard drive? If you have worked with a floppy disk you
 +
already understand something about hard drives. Basically the
 +
hard drive unit is a sealed chamber (sealed against dust and
 +
dirt) which contains rapidly spinning single or multiple stacked
 +
platters. The platter(s) are similar to a floppy disk in that
 +
they store information magnetically - data can be erased and
 +
rewritten as needed. The trick is, however, that the storage
 +
capability is immense on a hard drive.
  
      What is a hard drive? If you have worked with a floppy disk you
+
A floppy typically holds about one third of a million computer
      already understand something about hard drives. Basically the  
+
characters (360,000 or 360K bytes). The hard drive can commonly
      hard drive unit is a sealed chamber (sealed against dust and  
+
hold 20 to 40 million (or more!) bytes or computer words. In
      dirt) which contains rapidly spinning single or multiple stacked
+
addition, the hard drive motor spins the magnetic platter
      platters. The platter(s) are similar to a floppy disk in that
+
quickly so that information is transferred rapidly rather than
      they store information magnetically - data can be erased and
+
the tedious rate of the leisurely spinning floppy. A small
      rewritten as needed. The trick is, however, that the storage
+
read/write head hovers and moves above the hard drive magnetic
      capability is immense on a hard drive.  
+
platter much like a phonograph needle above a record. The
 +
difference is that the read/write head of the hard drive rides
 +
slightly above the platter on a thin cushion of air. In the
 +
floppy drive mechanism, the read/write head is in direct contact
 +
with the floppy. All hard drives are installed in two parts: the  
 +
drive (a box containing the disk and read/write head) and the
 +
controller (a circuit board) which may be integrated into the
 +
drive or a separate circuit board. The hard drive stores the
 +
information. The controller assumes the role of a high speed
 +
"translator/traffic cop" to help the hard drive move its massive
 +
amount of information smoothly.  
  
      A floppy typically holds about one third of a million computer
+
Back to the magnetic platter for a moment. The read write heads
      characters (360,000 or 360K bytes). The hard drive can commonly
+
are mounted on a moveable arm and each position of the head
      hold 20 to 40 million (or more!) bytes or computer words. In
+
above the platter defines a circular TRACK just like the track
      addition, the hard drive motor spins the magnetic platter  
+
of a phonograph record. As the arm changes positions, different
      quickly so that information is transferred rapidly rather than
+
circular tracks are traced magnetically upon the surface of the  
      the tedious rate of the leisurely spinning floppy. A small
+
platter. Most hard drives have several read/write heads which
      read/write head hovers and moves above the hard drive magnetic
+
service both the top and bottom of each platter. A set of tracks
      platter much like a phonograph needle above a record. The
+
on different platters define a vertical CYLINDER somewhat like
      difference is that the read/write head of the hard drive rides
+
the surface of a tin can whose top and bottom are missing. Large
      slightly above the platter on a thin cushion of air. In the
+
hard drives can have six or more platters and therefore 12 or
      floppy drive mechanism, the read/write head is in direct contact
+
more sides for information storage. The tracks can also be
      with the floppy. All hard drives are installed in two parts: the
+
defined as divisions of equally divided data called SECTORS
      drive (a box containing the disk and read/write head) and the
+
which are something like portions of the outer edge of a circle.
      controller (a circuit board) which may be integrated into the  
+
Finally, the sum collection of tracks, sectors and cylinders
      drive or a separate circuit board. The hard drive stores the
+
define the entire VOLUME of the hard disk.  
      information. The controller assumes the role of a high speed
 
      "translator/traffic cop" to help the hard drive move its massive
 
      amount of information smoothly.  
 
  
      Back to the magnetic platter for a moment. The read write heads  
+
Each piece of data has an address which tells the read/write  
      are mounted on a moveable arm and each position of the head
+
heads where to move to locate that specific piece of  
      above the platter defines a circular TRACK just like the track
+
information. If you tell the read/write heads to move to and  
      of a phonograph record. As the arm changes positions, different
+
hover over a specific track, sooner or later your data will pass
      circular tracks are traced magnetically upon the surface of the
+
beneath it. Since you can move the heads directly to a given
      platter. Most hard drives have several read/write heads which
+
track quickly, the early nomenclature for a hard drive was the
      service both the top and bottom of each platter. A set of tracks
+
DASD or DIRECT ACCESS STORAGE DEVICE.  
      on different platters define a vertical CYLINDER somewhat like
 
      the surface of a tin can whose top and bottom are missing. Large
 
      hard drives can have six or more platters and therefore 12 or  
 
      more sides for information storage. The tracks can also be
 
      defined as divisions of equally divided data called SECTORS
 
      which are something like portions of the outer edge of a circle.
 
      Finally, the sum collection of tracks, sectors and cylinders
 
      define the entire VOLUME of the hard disk.  
 
  
      Each piece of data has an address which tells the read/write  
+
Movement of the read/write head arm takes a little time. For
      heads where to move to locate that specific piece of
+
this reason an ACCESS TIME is associated with hard drives and
      information. If you tell the read/write heads to move to and  
+
stated in advertising and specification sheets. Generally this
      hover over a specific track, sooner or later your data will pass
+
time is stated as the AVERAGE ACCESS TIME and is frequently in
      beneath it. Since you can move the heads directly to a given
+
the thousandths of seconds or millisecond range which is fast
      track quickly, the early nomenclature for a hard drive was the
+
indeed. The old IBM XT class machines featured access times
      DASD or DIRECT ACCESS STORAGE DEVICE.  
+
around 85 milliseconds with the AT class machines featuring
 +
access times around 40 seconds. Newer hard drives post times in
 +
the 28 to 15 millisecond access range. Remember, the faster you  
 +
can move the read/write heads, the faster you can get to your
 +
data.  
  
      Movement of the read/write head arm takes a little time. For
+
The AVERAGE WAIT TIME is a less frequently discussed number but
      this reason an ACCESS TIME is associated with hard drives and
+
equally interesting. Once the read/write head is positioned over
      stated in advertising and specification sheets. Generally this
+
the track holding your data, the system must wait for the
      time is stated as the AVERAGE ACCESS TIME and is frequently in
+
correct sector to pass beneath. Obviously, the average wait time  
      the thousandths of seconds or millisecond range which is fast
+
is one half the time it takes for a full rotation of the
      indeed. The old IBM XT class machines featured access times
+
platter. This figure is rarely given in advertisements and is  
      around 85 milliseconds with the AT class machines featuring
+
usually comparable for most drives of the same type and is  
      access times around 40 seconds. Newer hard drives post times in
+
generally much shorter than the access time. Speed matters to a
      the 28 to 15 millisecond access range. Remember, the faster you  
+
hard drive! Average wait time is published if you dig it out of
      can move the read/write heads, the faster you can get to your
+
the specification sheet or write to the manufacturer.  
      data.  
 
  
      The AVERAGE WAIT TIME is a less frequently discussed number but
+
An extension of this logic brings us to consider the INTERLEAVE
      equally interesting. Once the read/write head is positioned over
+
FACTOR for a disk. Generally a hard drive reads and writes
      the track holding your data, the system must wait for the
+
information in sectors of the same, repeatable size such as 512
      correct sector to pass beneath. Obviously, the average wait time
+
bytes. However programs and data files are usually much bigger
      is one half the time it takes for a full rotation of the
+
than this and obviously must be scattered onto many sectors. The
      platter. This figure is rarely given in advertisements and is
+
problem is that the disk rotation is much too fast for a large
      usually comparable for most drives of the same type and is
+
file to be written in perfectly contiguous sectors on the same  
      generally much shorter than the access time. Speed matters to a  
+
track. If you tried to write the data onto a track, one byte
      hard drive! Average wait time is published if you dig it out of
+
after the next, the central processing unit chip or CPU could
      the specification sheet or write to the manufacturer.  
+
not absorb the data fast enough.
  
      An extension of this logic brings us to consider the INTERLEAVE
+
The solution is to place sectors to be read in ALTERNATING
      FACTOR for a disk. Generally a hard drive reads and writes
+
fashion which gives the CPU time to digest the data. Thus if a  
      information in sectors of the same, repeatable size such as 512
+
circular track on the platter had 8 sectors you might number and  
      bytes. However programs and data files are usually much bigger
+
read them in this order: 1,5,2,6,3,7,4,8. This way the CPU has a
      than this and obviously must be scattered onto many sectors. The  
+
"breather" in between each sector read. The number of rotations
      problem is that the disk rotation is much too fast for a large
+
it takes the heads to read ALL tracks in succession is the  
      file to be written in perfectly contiguous sectors on the same
+
INTERLEAVE FACTOR. Slow CPU chips can force a disk to use an
      track. If you tried to write the data onto a track, one byte
+
interleave factor of 3 or even 4. A faster processor might be
      after the next, the central processing unit chip or CPU could
+
able to handle a disk interleave of 1:2 (such as 80286 processor
      not absorb the data fast enough.
+
chips) or even 1:1 (such as 80386 processor chips.) It is  
 +
possible to low level format a disk and change its interleave
 +
factor; but if the CPU cannot keep up, the adjustment is
 +
worthless. To the processor operating in millionths of a second,  
 +
the time drain of waiting for a hard drive which operates in
 +
thousandths of a second or floppy drive which operates in tenths
 +
and full seconds is wasted time. The obvious point of logic is
 +
that when using a hard drive you need to organize files for
 +
minimum time delays for the processor.  
  
      The solution is to place sectors to be read in ALTERNATING
+
The first outer track on a disk is always the boot record which
      fashion which gives the CPU time to digest the data. Thus if a
+
loads the main portions of DOS into the machine. Following this
      circular track on the platter had 8 sectors you might number and
+
is the file allocation table or FAT which we discussed in
      read them in this order: 1,5,2,6,3,7,4,8. This way the CPU has a
+
earlier tutorials. The FAT maintains data in CLUSTERS which, for
      "breather" in between each sector read. The number of rotations
+
an XT class machine are 4096 bytes. On the AT class machine the  
      it takes the heads to read ALL tracks in succession is the  
+
cluster size is 2048 bytes which is much more efficient and less
      INTERLEAVE FACTOR. Slow CPU chips can force a disk to use an
+
wasteful of disk space. Following the FAT are the sectors for
      interleave factor of 3 or even 4. A faster processor might be
+
the root directory of the hard drive. Each directory entry is 32
      able to handle a disk interleave of 1:2 (such as 80286 processor
+
bytes in length. Curiously, and to our good advantage, unused
      chips) or even 1:1 (such as 80386 processor chips.) It is  
+
entries in the directory have a unique first character byte.
      possible to low level format a disk and change its interleave
+
When a file is deleted though DOS, ONLY the first character is  
      factor; but if the CPU cannot keep up, the adjustment is
+
reset.  
      worthless. To the processor operating in millionths of a second,
 
      the time drain of waiting for a hard drive which operates in
 
      thousandths of a second or floppy drive which operates in tenths
 
      and full seconds is wasted time. The obvious point of logic is  
 
      that when using a hard drive you need to organize files for
 
      minimum time delays for the processor.  
 
  
      The first outer track on a disk is always the boot record which
+
Fortunately this allows various utility programs to attempt to
      loads the main portions of DOS into the machine. Following this
+
recover the deleted file since ONLY the directory data is
      is the file allocation table or FAT which we discussed in
+
altered but NOT the file itself. However, as time goes on and
      earlier tutorials. The FAT maintains data in CLUSTERS which, for
+
additional files are added to the disk, the original file is
      an XT class machine are 4096 bytes. On the AT class machine the  
+
overwritten by new information. This is why you need to act
      cluster size is 2048 bytes which is much more efficient and less
+
immediately if you discover you have accidentally deleted a
      wasteful of disk space. Following the FAT are the sectors for
+
file. An advantage to the use of the FAT is that files do not
      the root directory of the hard drive. Each directory entry is 32
+
have to be given a fixed amount of space on a disk - they can
      bytes in length. Curiously, and to our good advantage, unused
+
use as many or few clusters as needed. The downside is that the  
      entries in the directory have a unique first character byte.
+
file pieces can be scattered wildly over the surface of the disk
      When a file is deleted though DOS, ONLY the first character is  
+
in a non contiguous fashion which only the FAT can track. This
      reset.  
+
means more read/write head motion and more wasted time as far as
 +
the CPU and the performance of your program is concerned.  
  
      Fortunately this allows various utility programs to attempt to
+
Additionally, if you have many deleted files within the  
      recover the deleted file since ONLY the directory data is
+
directory, DOS must search tediously through each one from top
      altered but NOT the file itself. However, as time goes on and
+
to bottom of the directory to find a match for the file you are
      additional files are added to the disk, the original file is
+
trying to locate. Obviously, then, programs and data of high use
      overwritten by new information. This is why you need to act
+
should have their directory entries located near the top of the  
      immediately if you discover you have accidentally deleted a
+
directory to speed the search. Each time the read/write head
      file. An advantage to the use of the FAT is that files do not
+
moves takes time: searching the directory and finding the pieces  
      have to be given a fixed amount of space on a disk - they can
+
of the scattered file all take movement of the read/write arm.
      use as many or few clusters as needed. The downside is that the  
+
There are several ways to unfragment files which boost disk
      file pieces can be scattered wildly over the surface of the disk
+
performance, and we'll talk about those techniques it a bit.  
      in a non contiguous fashion which only the FAT can track. This
 
      means more read/write head motion and more wasted time as far as
 
      the CPU and the performance of your program is concerned.  
 
  
      Additionally, if you have many deleted files within the
 
      directory, DOS must search tediously through each one from top
 
      to bottom of the directory to find a match for the file you are
 
      trying to locate. Obviously, then, programs and data of high use
 
      should have their directory entries located near the top of the
 
      directory to speed the search. Each time the read/write head
 
      moves takes time: searching the directory and finding the pieces
 
      of the scattered file all take movement of the read/write arm.
 
      There are several ways to unfragment files which boost disk
 
      performance, and we'll talk about those techniques it a bit.
 
  
      ----------------------------------------------------------------
 
 
   
 
   
              HARD DISKS - STRATEGIES FOR TURBOCHARGED RESULTS
 
  
      ----------------------------------------------------------------  
+
HARD DISKS - STRATEGIES FOR TURBOCHARGED RESULTS
  
      Before we examine methods for improving hard drive performance,
 
      several simple "care and feeding" precautions should be
 
      mentioned.
 
  
      Hard drives are touchy if mistreated! Once brought up to speed,  
+
Before we examine methods for improving hard drive performance,
      a hard drive should never be bumped or moved. The read/write  
+
several simple "care and feeding" precautions should be
      head (similar to the phonograph needle resting on a record) will  
+
mentioned.
      smash or chip into the surface of the spinning hard drive  
+
 
      platter and take your data with it. Either the head or the  
+
Hard drives are touchy if mistreated! Once brought up to speed,  
      magnetically coated platter can be permanently damaged. Allow  
+
a hard drive should never be bumped or moved. The read/write  
      the hard drive to some to a complete stop before moving the  
+
head (similar to the phonograph needle resting on a record) will  
      computer.  
+
smash or chip into the surface of the spinning hard drive  
 +
platter and take your data with it. Either the head or the  
 +
magnetically coated platter can be permanently damaged. Allow  
 +
the hard drive to some to a complete stop before moving the  
 +
computer.  
 
        
 
        
      In addition always use a "parking" software package to move the  
+
In addition always use a "parking" software package to move the  
      read/write head to the safety zone before turning off the  
+
read/write head to the safety zone before turning off the  
      computer. A parking program usually accompanies most computers  
+
computer. A parking program usually accompanies most computers  
      which have hard drives installed or can be obtained from  
+
which have hard drives installed or can be obtained from  
      commercial or shareware sources. A few drives automatically park  
+
commercial or shareware sources. A few drives automatically park  
      the heads when turned off but this tends to be a rare feature  
+
the heads when turned off but this tends to be a rare feature  
      seen mostly on high priced hard drives.  
+
seen mostly on high priced hard drives.  
  
      Always maintain copies of data and programs outside the hard  
+
Always maintain copies of data and programs outside the hard  
      drive by "backing up" onto a floppy or tape. How often should  
+
drive by "backing up" onto a floppy or tape. How often should  
      you back up your files? Daily if you use the computer to produce  
+
you back up your files? Daily if you use the computer to produce  
      many changes to important documents. Weekly backup is probably a  
+
many changes to important documents. Weekly backup is probably a  
      bare minimum considered reasonable for occasional computer  
+
bare minimum considered reasonable for occasional computer  
      users. Other computer users maintain vital data on floppies or  
+
users. Other computer users maintain vital data on floppies or  
      other backup systems and use the hard drive to store programs or  
+
other backup systems and use the hard drive to store programs or  
      applications only such as a spreadsheet or database. Backups are  
+
applications only such as a spreadsheet or database. Backups are  
      a good idea even for floppy disk systems which have no hard  
+
a good idea even for floppy disk systems which have no hard  
      drive.  
+
drive.  
 
        
 
        
      Make two copies of every file regardless of whether you have a  
+
Make two copies of every file regardless of whether you have a  
      hard drive or not. Some shareware and commercial utilities ease  
+
hard drive or not. Some shareware and commercial utilities ease  
      the backup chore by only copying those files to a floppy which  
+
the backup chore by only copying those files to a floppy which  
      have been changed or updated since the last backup has been  
+
have been changed or updated since the last backup has been  
      performed. They ignore files which have not changed and thus do  
+
performed. They ignore files which have not changed and thus do  
      not require copying again. This can save a lot of time when  
+
not require copying again. This can save a lot of time when  
      backing up valuable files from your hard drive to a floppy for  
+
backing up valuable files from your hard drive to a floppy for  
      safekeeping.  
+
safekeeping.  
 
                
 
                
      Hard drives should periodically be reorganized (files  
+
Hard drives should periodically be reorganized (files  
      unfragmented) to ensure speedy retrieval and access to data.  
+
unfragmented) to ensure speedy retrieval and access to data.  
      Inexpensive or free software programs known as "disk file  
+
Inexpensive or free software programs known as "disk file  
      unfragmenters" do this job nicely. As disk files are created and  
+
unfragmenters" do this job nicely. As disk files are created and  
      deleted, blank spaces and unused sectors begin to build up.  
+
deleted, blank spaces and unused sectors begin to build up.  
 
        
 
        
      Gradually files are broken into pieces and scattered over the  
+
Gradually files are broken into pieces and scattered over the  
      many tracks and sectors of the disk. This happens to both  
+
many tracks and sectors of the disk. This happens to both  
      floppies and hard drives, but is especially annoying on hard  
+
floppies and hard drives, but is especially annoying on hard  
      drives because of the dramatic increase in time it takes to load  
+
drives because of the dramatic increase in time it takes to load  
      a program or data file. The File allocation table is the  
+
a program or data file. The File allocation table is the  
      culprit, sense all data is packed away in the first and handiest  
+
culprit, sense all data is packed away in the first and handiest  
      sector on the drive which the FAT can find.  
+
sector on the drive which the FAT can find.  
  
      The FAT allows files to be fragmented down to the cluster level.  
+
The FAT allows files to be fragmented down to the cluster level.  
      One way to unfragment a disk is to copy all of the files off to  
+
One way to unfragment a disk is to copy all of the files off to  
      floppies and then recopy them back to the hard drive - a tedious  
+
floppies and then recopy them back to the hard drive - a tedious  
      nuisance at best. You would do this with the DOS XCOPY or COPY  
+
nuisance at best. You would do this with the DOS XCOPY or COPY  
      commands but not DISKCOPY since this would retain the tracks and  
+
commands but not DISKCOPY since this would retain the tracks and  
      their fragmentation as you first found them.  
+
their fragmentation as you first found them.  
 
        
 
        
      Defragmenting programs perform this task without requiring  
+
Defragmenting programs perform this task without requiring  
      removal of the files from the hard drive. They perform their  
+
removal of the files from the hard drive. They perform their  
      magic by moving around the clusters of a scattered file in such  
+
magic by moving around the clusters of a scattered file in such  
      a way as to reassemble it into contiguous pieces again. Some  
+
a way as to reassemble it into contiguous pieces again. Some  
      customization is permitted with the more sophisticated  
+
customization is permitted with the more sophisticated  
      "defragmenting" programs. For example, subdirectory files can be  
+
"defragmenting" programs. For example, subdirectory files can be  
      relocated after the root or below a different subdirectory or,  
+
relocated after the root or below a different subdirectory or,  
      in another example, high use files might be placed higher in the  
+
in another example, high use files might be placed higher in the  
      directory listing for faster disk access.  
+
directory listing for faster disk access.  
 
        
 
        
      The first time a defragmenting program is run may require  
+
The first time a defragmenting program is run may require  
      several hours if a hard drive is large and badly fractured with  
+
several hours if a hard drive is large and badly fractured with  
      scattered files and clusters. It is a good idea to backup all  
+
scattered files and clusters. It is a good idea to backup all  
      essential files prior to "defragging" just in case there is a  
+
essential files prior to "defragging" just in case there is a  
      power failure during a long "defrag". Subsequent runs of the  
+
power failure during a long "defrag". Subsequent runs of the  
      "defragger" produce runs of only a few minutes or so since the  
+
"defragger" produce runs of only a few minutes or so since the  
      heavy work was done earlier. Essentially, "defragging" the hard  
+
heavy work was done earlier. Essentially, "defragging" the hard  
      drive should be done regularaly, perhaps weekly. Defragging is  
+
drive should be done regularaly, perhaps weekly. Defragging is  
      not a substitute for caching, ramdisks, or buffer - instead it  
+
not a substitute for caching, ramdisks, or buffer - instead it  
      is a maintenance function which should be done regularly.  
+
is a maintenance function which should be done regularly.  
  
      Yet another possible avenue to improve disk performance is that  
+
Yet another possible avenue to improve disk performance is that  
      of changing the disk interleave factor which we will discuss a  
+
of changing the disk interleave factor which we will discuss a  
      bit later in this tutorial. By way of brief introduction: the  
+
bit later in this tutorial. By way of brief introduction: the  
      disk interleave indicates how many revolutions of the magnetic  
+
disk interleave indicates how many revolutions of the magnetic  
      platter are required to read all the sectors of data from the  
+
platter are required to read all the sectors of data from the  
      spinning track. A ratio of 1:1 means all data can be read  
+
spinning track. A ratio of 1:1 means all data can be read  
      sequentially. One sector of data after another.  
+
sequentially. One sector of data after another.  
  
      There is some overhead time required for the read/write head to  
+
There is some overhead time required for the read/write head to  
      zip to the FAT area of the disk (if it is not in a cache or  
+
zip to the FAT area of the disk (if it is not in a cache or  
      buffer) to determine location of the next sector along the disk  
+
buffer) to determine location of the next sector along the disk  
      track.  
+
track.  
 
        
 
        
      For example, five clusters of data on a track might require four  
+
For example, five clusters of data on a track might require four  
      trips back to the FAT track to find the cluster addresses even  
+
trips back to the FAT track to find the cluster addresses even  
      on a completely defragmented disk. We will talk more about  
+
on a completely defragmented disk. We will talk more about  
      cluster and defragmenting a bit later in this tutorial.  
+
cluster and defragmenting a bit later in this tutorial.  
 
        
 
        
      Nevertheless, depending on the speed of your central processor  
+
Nevertheless, depending on the speed of your central processor  
      or CPU, using a program which tests and alters the interleave  
+
or CPU, using a program which tests and alters the interleave  
      factor, IF THIS CAN BE DONE, may yield better performance. Most  
+
factor, IF THIS CAN BE DONE, may yield better performance. Most  
      interleave adjustment software first performs a test to  
+
interleave adjustment software first performs a test to  
      determine the current interleave, the possible changes and of  
+
determine the current interleave, the possible changes and of  
      course how much performance time might be gained. A few of these  
+
course how much performance time might be gained. A few of these  
      packages can alter the interleave with the files in place but  
+
packages can alter the interleave with the files in place but  
      you should backup truly essential files before starting the  
+
you should backup truly essential files before starting the  
      process. Interleave factor adjustment are mainly derived from  
+
process. Interleave factor adjustment are mainly derived from  
      the CPU speed NOT the disk speed. Thus a fast AT or 80386  
+
the CPU speed NOT the disk speed. Thus a fast AT or 80386  
      equipped machine will more likely be able to take advantage of  
+
equipped machine will more likely be able to take advantage of  
      an interleave adjustment.  
+
an interleave adjustment.  
  
      Tinkering with a hard drive for optimum results might best be  
+
Tinkering with a hard drive for optimum results might best be  
      divided into two categories: DISK SUBSTITUTION and DISK  
+
divided into two categories: DISK SUBSTITUTION and DISK  
      ALTERATION. DOS allows two clever ways substituting RAM memory  
+
ALTERATION. DOS allows two clever ways substituting RAM memory  
      for disk memory.  
+
for disk memory.  
  
      In the first, using BUFFERS, the small CONFIG.SYS file on your  
+
In the first, using BUFFERS, the small CONFIG.SYS file on your  
      hard drive is modified to contain a buffers statement. A sample  
+
hard drive is modified to contain a buffers statement. A sample  
      might be: BUFFERS=20. A DOS buffer is an area of RAM memory  
+
might be: BUFFERS=20. A DOS buffer is an area of RAM memory  
      capable of holding a 512 byte mirror image of a disk sector.  
+
capable of holding a 512 byte mirror image of a disk sector.  
      This allows DOS to quickly search the buffer area for frequently  
+
This allows DOS to quickly search the buffer area for frequently  
      used data instead of the slower disk. In the older XT class  
+
used data instead of the slower disk. In the older XT class  
      machine, if you did not specify a buffer size, DOS defaulted to  
+
machine, if you did not specify a buffer size, DOS defaulted to  
      2 buffers while later versions of DOS default to about 10  
+
2 buffers while later versions of DOS default to about 10  
      buffers. Most users settle on about 20 buffers but you can  
+
buffers. Most users settle on about 20 buffers but you can  
      specify up to 99 with current releases of DOS. But you don't get  
+
specify up to 99 with current releases of DOS. But you don't get  
      something for nothing. If you used the full 99 buffers  
+
something for nothing. If you used the full 99 buffers  
      available, you would soak up 45K of your main RAM memory! The  
+
available, you would soak up 45K of your main RAM memory! The  
      downside of using buffers is that more is not necessarily  
+
downside of using buffers is that more is not necessarily  
      better.  
+
better.  
  
      Unfortunately, DOS searches the buffer area of RAM sequentially  
+
Unfortunately, DOS searches the buffer area of RAM sequentially  
      rather than logically so if DOS requires data which is in the  
+
rather than logically so if DOS requires data which is in the  
      buffer area, it will search each 512 byte area in sequence from  
+
buffer area, it will search each 512 byte area in sequence from  
      top to bottom even though the data it needs may be at the end of  
+
top to bottom even though the data it needs may be at the end of  
      the buffer. Logically, then, there is an optimum number of  
+
the buffer. Logically, then, there is an optimum number of  
      buffers - too many used with a small program and you can slow  
+
buffers - too many used with a small program and you can slow  
      things down, not enough and DOS will be forced to go out to the  
+
things down, not enough and DOS will be forced to go out to the  
      disk to retrieve what it needs. If you rarely use the same data  
+
disk to retrieve what it needs. If you rarely use the same data  
      within a program twice but load lots of different programs and  
+
within a program twice but load lots of different programs and  
      data, a large number of buffers won't help. However if you need  
+
data, a large number of buffers won't help. However if you need  
      frequent access to a certain data file or portion of that file,  
+
frequent access to a certain data file or portion of that file,  
      buffers will help. Portions of the FAT are kept within the  
+
buffers will help. Portions of the FAT are kept within the  
      buffers area, so dropping your buffers to zero has the damaging  
+
buffers area, so dropping your buffers to zero has the damaging  
      effect that DOS must always go to the disk to read the FAT which  
+
effect that DOS must always go to the disk to read the FAT which  
      isn't helpful either.  
+
isn't helpful either.  
  
      Another  way of substituting RAM memory for disk memory involves  
+
Another  way of substituting RAM memory for disk memory involves  
      using a RAMDISK. The idea is to create in RAM memory an entire  
+
using a RAMDISK. The idea is to create in RAM memory an entire  
      disk or a small portion of a disk. This works like magic on many  
+
disk or a small portion of a disk. This works like magic on many  
      machines since the reading of tracks and sectors takes place at  
+
machines since the reading of tracks and sectors takes place at  
      the high speed of RAM memory rather than the mechanically  
+
the high speed of RAM memory rather than the mechanically  
      limited speed of the read/write heads on a floppy or hard drive.  
+
limited speed of the read/write heads on a floppy or hard drive.  
  
      But be careful. Three areas of difficulty can arise. First you  
+
But be careful. Three areas of difficulty can arise. First you  
      must remember to take the data from a floppy or hard drive and  
+
must remember to take the data from a floppy or hard drive and  
      move it into the RAMDISK. Many people do this automatically from  
+
move it into the RAMDISK. Many people do this automatically from  
      within an AUTOEXEC.BAT file or may have several floppies, each  
+
within an AUTOEXEC.BAT file or may have several floppies, each  
      with a different RAMDISK configuration depending on the task at  
+
with a different RAMDISK configuration depending on the task at  
      hand. Copying data to the RAMDISK usually moves along briskly.  
+
hand. Copying data to the RAMDISK usually moves along briskly.  
      Secondly you must sacrifice a large area of memory for the  
+
Secondly you must sacrifice a large area of memory for the  
      RAMDISK which can no longer be used by your main program. Users  
+
RAMDISK which can no longer be used by your main program. Users  
      of computers with extended or expanded memory usually choose to  
+
of computers with extended or expanded memory usually choose to  
      put their RAMDISK in the extended or expanded memory area of RAM  
+
put their RAMDISK in the extended or expanded memory area of RAM  
      so that precious main memory is not lost. Still, a small RAMDISK  
+
so that precious main memory is not lost. Still, a small RAMDISK  
      can soak up 64K of RAM memory and one or two MEG RAMDISKS area  
+
can soak up 64K of RAM memory and one or two MEG RAMDISKS area  
      common for many users. The third and most serious problem when  
+
common for many users. The third and most serious problem when  
      using RAMDISKS is that they are volatile - switch off the  
+
using RAMDISKS is that they are volatile - switch off the  
      machine or experience a power failure, and your data is lost  
+
machine or experience a power failure, and your data is lost  
      forever! Rather than residing safely on a magnetic disk, the  
+
forever! Rather than residing safely on a magnetic disk, the  
      data is "floating" in RAM memory and should be - MUST BE! -  
+
data is "floating" in RAM memory and should be - MUST BE! -  
      written to a disk before the machine is powered down.  
+
written to a disk before the machine is powered down.  
  
      Many applications fly with a RAMDISK. Users of word processors  
+
Many applications fly with a RAMDISK. Users of word processors  
      find that moving the spelling checker and thesaurus to the  
+
find that moving the spelling checker and thesaurus to the  
      RAMDISK speeds up things considerably since these are used  
+
RAMDISK speeds up things considerably since these are used  
      heavily in a random manner. Spreadsheet users find that reading  
+
heavily in a random manner. Spreadsheet users find that reading  
      and writing short data files to RAMDISKS is a boon. Programs  
+
and writing short data files to RAMDISKS is a boon. Programs  
      which use overlay files or temporary files as well as  
+
which use overlay files or temporary files as well as  
      programming compilers benefit from RAMDISK use. Batch files  
+
programming compilers benefit from RAMDISK use. Batch files  
      which are disk intensive as well as small utilities really  
+
which are disk intensive as well as small utilities really  
      sprint when placed on a RAMDISK. Basically, any program file  
+
sprint when placed on a RAMDISK. Basically, any program file  
      which is frequently used and loaded/unloaded repeatedly to a  
+
which is frequently used and loaded/unloaded repeatedly to a  
      disk during normal computer operation is an excellent candidate  
+
disk during normal computer operation is an excellent candidate  
      for RAMDISK placement. DOS contains a RAMDISK which is called by  
+
for RAMDISK placement. DOS contains a RAMDISK which is called by  
      using the statement DEVICE=VDISK.SYS or DEVICE=RAMDRIVE.SYS (if  
+
using the statement DEVICE=VDISK.SYS or DEVICE=RAMDRIVE.SYS (if  
      you are using MSDOS) which is placed in your CONFIG.SYS file.  
+
you are using MSDOS) which is placed in your CONFIG.SYS file.  
      Your DOS manual details the specifics such as stating the size  
+
Your DOS manual details the specifics such as stating the size  
      of RAMDISK and giving it a drive letter. You must still copy  
+
of RAMDISK and giving it a drive letter. You must still copy  
      your target files into the RAMDISK and place it in the search  
+
your target files into the RAMDISK and place it in the search  
      path (with the PATH=  command) as we mentioned in a previous  
+
path (with the PATH=  command) as we mentioned in a previous  
      tutorial. And the RAMDISK should always be the first drive  
+
tutorial. And the RAMDISK should always be the first drive  
      letter mentioned in the path command so that DOS searches it  
+
letter mentioned in the path command so that DOS searches it  
      first for optimum results.  
+
first for optimum results.  
  
      Yet another area of investigation is that of CACHE software.  
+
Yet another area of investigation is that of CACHE software.  
      Essentially a CACHE is an extension of the buffers idea we  
+
Essentially a CACHE is an extension of the buffers idea we  
      discussed earlier. But the twist is that the CACHE is searched  
+
discussed earlier. But the twist is that the CACHE is searched  
      intelligently by a searching algorithm within the CACHE software  
+
intelligently by a searching algorithm within the CACHE software  
      rather than from top to bottom as with the more typical DOS  
+
rather than from top to bottom as with the more typical DOS  
      buffer search system. Disk CACHE software can be obtained as  
+
buffer search system. Disk CACHE software can be obtained as  
      either commercial software or shareware. As with a RAMDISK, the  
+
either commercial software or shareware. As with a RAMDISK, the  
      CACHE requires a chunk of RAM memory to operate. This can be  
+
CACHE requires a chunk of RAM memory to operate. This can be  
      extended memory, expanded memory or main RAM memory. Some  
+
extended memory, expanded memory or main RAM memory. Some  
      manufacturers include a CACHE program with the software package  
+
manufacturers include a CACHE program with the software package  
      or DOS disk. A CACHE is a sophisticated type of RAMDISK, in a  
+
or DOS disk. A CACHE is a sophisticated type of RAMDISK, in a  
      rough sense.  
+
rough sense.  
  
      CACHE software allocates a large area of memory for storage of  
+
CACHE software allocates a large area of memory for storage of  
      frequently used disk data. This data is updated by an  
+
frequently used disk data. This data is updated by an  
      intelligent CACHE search algorithm in an attempt to "guess"  
+
intelligent CACHE search algorithm in an attempt to "guess"  
      which tracks of a disk you might read or need next. The CACHE  
+
which tracks of a disk you might read or need next. The CACHE  
      also stores the most frequently used disk data and attempts to  
+
also stores the most frequently used disk data and attempts to  
      remove less frequently used data. Whenever DOS requests disk  
+
remove less frequently used data. Whenever DOS requests disk  
      data, the CACHE software first tries to fill the order from data  
+
data, the CACHE software first tries to fill the order from data  
      currently stashed in the CACHE which prevents a slower disk  
+
currently stashed in the CACHE which prevents a slower disk  
      search.  
+
search.  
 
        
 
        
      When data is written from the program to the CACHE, first a disk  
+
When data is written from the program to the CACHE, first a disk  
      write is done to prevent data loss in case of power failure and  
+
write is done to prevent data loss in case of power failure and  
      then the data is stashed in the CACHE in case it is needed  
+
then the data is stashed in the CACHE in case it is needed  
      again. Usually the hard drive data is the target of the CACHE  
+
again. Usually the hard drive data is the target of the CACHE  
      activity, but a floppy disk could also be cached. All CACHE  
+
activity, but a floppy disk could also be cached. All CACHE  
      software allows you to allocate the size of the CACHE as well as  
+
software allows you to allocate the size of the CACHE as well as  
      the drive or drives to be cached. And some even allow you to  
+
the drive or drives to be cached. And some even allow you to  
      specify exact files or data to be cached. The key is that high  
+
specify exact files or data to be cached. The key is that high  
      use data lives in RAM memory which keeps tedious disk access  
+
use data lives in RAM memory which keeps tedious disk access  
      times low. In general, if your computer has a megabyte or more  
+
times low. In general, if your computer has a megabyte or more  
      of memory and a speedy processor such as an 80286 or 80386  
+
of memory and a speedy processor such as an 80286 or 80386  
      either or both a CACHE or RAMDISK option does improve  
+
either or both a CACHE or RAMDISK option does improve  
      performance.  
+
performance.
 +
 
 +
As we leave hard disk boot camp, let's finally look at hard
 +
drive formatting processes. Two basic formatting operations are
 +
of concern: physical formatting or low level formatting and
 +
logical or high level formatting. When you use the format
 +
program on a floppy disk both low level and high level
 +
formatting is accomplished. On a hard disk, formatting performs
 +
only logical or high level formatting. On a hard disk, low level
 +
formatting is usually done to a disk before shipment. As an
 +
aside, the FDISK command of DOS has little to do with either
 +
type of formatting, but is a method of partitioning or arranging
 +
the data onto the hard drive tracks. Each disk platter is
 +
separated into circular concentric tracks where data is stored
 +
as we saw earlier. During physical formatting the tracks are
 +
divided into further subdivisions called clusters and further
 +
yet into sectors. High level formatting involves the specific
 +
ordering of the space for the exclusive use of DOS and is a bit
 +
more analogous to the formatting of a floppy disk.  
  
      As we leave hard disk boot camp, let's finally look at hard
+
Some software programs of use by hard drive owners:
      drive formatting processes. Two basic formatting operations are
 
      of concern: physical formatting or low level formatting and
 
      logical or high level formatting. When you use the format
 
      program on a floppy disk both low level and high level
 
      formatting is accomplished. On a hard disk, formatting performs
 
      only logical or high level formatting. On a hard disk, low level
 
      formatting is usually done to a disk before shipment. As an
 
      aside, the FDISK command of DOS has little to do with either
 
      type of formatting, but is a method of partitioning or arranging
 
      the data onto the hard drive tracks. Each disk platter is
 
      separated into circular concentric tracks where data is stored
 
      as we saw earlier. During physical formatting the tracks are
 
      divided into further subdivisions called clusters and further
 
      yet into sectors. High level formatting involves the specific
 
      ordering of the space for the exclusive use of DOS and is a bit
 
      more analogous to the formatting of a floppy disk.
 
  
      Some software programs of use by hard drive owners:  
+
The following two programs perform low level formatting and
 +
simple diagnostic routines on a hard drive:  
  
      The following two programs perform low level formatting and  
+
Disk Manager and CheckIt
      simple diagnostic routines on a hard drive:
 
  
      Disk Manager and CheckIt
+
Data recovery and "unerasing" programs also containing
 +
diagnostic routines are:
  
      Data recovery and "unerasing" programs also containing
+
PC Tools Deluxe, Norton Utilities, Mace Utilities
      diagnostic routines are:
 
  
      PC Tools Deluxe, Norton Utilities, Mace Utilities
+
Extensive diagnostic and maintenance/data repair functions as
 +
well as interleave alteration and head parking are offered by:
  
      Extensive diagnostic and maintenance/data repair functions as
+
SpinRite II, Optune, Disk Technician
      well as interleave alteration and head parking are offered by:
 
  
      SpinRite II, Optune, Disk Technician
+
Shareware programs with unerase functions include:
  
      Shareware programs with unerase functions include:
+
Bakers Dozen
  
      Bakers Dozen
+
Shareware programs with defragmentation capabilities include:
  
      Shareware programs with defragmentation capabilities include:
+
SST and PACKDISK.
  
      SST and PACKDISK.
+
Tutorial finished. Be sure to order your FOUR BONUS DISKS which
 +
expand this software package with vital tools, updates and  
 +
additional tutorial material for laptop users!
  
      Tutorial finished. Be sure to order your FOUR BONUS DISKS which
 
      expand this software package with vital tools, updates and
 
      additional tutorial material for laptop users! Send $20.00 to
 
      Seattle Scientific Photography, Department LAP, PO Box 1506,
 
      Mercer Island, WA 98040. Bonus disks shipped promptly! Some
 
      portions of this software package use sections from the larger
 
      PC-Learn tutorial system which you will also receive with your
 
      order. Modifications, custom program versions, site and LAN
 
      licenses of this package for business or corporate use are
 
      possible, contact the author. This software is shareware - an
 
      honor system which means TRY BEFORE YOU BUY. Press escape key to
 
      return to menu.
 
</pre>
 
  
  
 
[[Category:Computing]]
 
[[Category:Computing]]
 +
[[Category:Essays]]

Revision as of 15:07, 26 December 2020

A simple observation: the first accessory any computer user should buy is hard drive. On a dollar for dollar basis nothing speeds up processing and expands convenience like a hard drive. The bad news? The substantial storage capacity of a hard drive contains the seeds of data catastrophe if you don't understand how to CAREFULLY maintain a hard drive. Some reference information pertaining to larger desktop hard drives as well as smaller laptop drives has been retained since drives in both computers are similar in function although different in form and size.

Many computer operations tend to slow down at the critical bottleneck of information transfer from computer memory (RAM) to disk. The faster the transfer, the faster the program operates. Nine times out of ten it is the bottleneck formed when information flows to or from a disk that you and your program must wait. This is where a hard drive really shines - speed.

Given the best possible treatment, a hard drive should last from eight to fifteen years. Drive manufacturers typically suggest 30,000 to 70,000 hours of routine life for a hard drive before failure. If you kept your PC on for a 40 hour work week for 50 weeks - you could expect about 15 years of service for a drive rated at 30,000 hours. Some hard drive users even suggest leaving the drive on continuously or alternatively turning it on in the morning and off at night to minimize motor and bearing wear since it is the starting shock which wears most heavily on a drive. However, given marginal treatment or abuse, you can expect about fifteen minutes of service followed by a $250 repair bill. Obviously a little information about hard drives and their care can't hurt.


TECHNOLOGY 101 - BOOT CAMP FOR HARD DRIVE USERS


What is a hard drive? If you have worked with a floppy disk you already understand something about hard drives. Basically the hard drive unit is a sealed chamber (sealed against dust and dirt) which contains rapidly spinning single or multiple stacked platters. The platter(s) are similar to a floppy disk in that they store information magnetically - data can be erased and rewritten as needed. The trick is, however, that the storage capability is immense on a hard drive.

A floppy typically holds about one third of a million computer characters (360,000 or 360K bytes). The hard drive can commonly hold 20 to 40 million (or more!) bytes or computer words. In addition, the hard drive motor spins the magnetic platter quickly so that information is transferred rapidly rather than the tedious rate of the leisurely spinning floppy. A small read/write head hovers and moves above the hard drive magnetic platter much like a phonograph needle above a record. The difference is that the read/write head of the hard drive rides slightly above the platter on a thin cushion of air. In the floppy drive mechanism, the read/write head is in direct contact with the floppy. All hard drives are installed in two parts: the drive (a box containing the disk and read/write head) and the controller (a circuit board) which may be integrated into the drive or a separate circuit board. The hard drive stores the information. The controller assumes the role of a high speed "translator/traffic cop" to help the hard drive move its massive amount of information smoothly.

Back to the magnetic platter for a moment. The read write heads are mounted on a moveable arm and each position of the head above the platter defines a circular TRACK just like the track of a phonograph record. As the arm changes positions, different circular tracks are traced magnetically upon the surface of the platter. Most hard drives have several read/write heads which service both the top and bottom of each platter. A set of tracks on different platters define a vertical CYLINDER somewhat like the surface of a tin can whose top and bottom are missing. Large hard drives can have six or more platters and therefore 12 or more sides for information storage. The tracks can also be defined as divisions of equally divided data called SECTORS which are something like portions of the outer edge of a circle. Finally, the sum collection of tracks, sectors and cylinders define the entire VOLUME of the hard disk.

Each piece of data has an address which tells the read/write heads where to move to locate that specific piece of information. If you tell the read/write heads to move to and hover over a specific track, sooner or later your data will pass beneath it. Since you can move the heads directly to a given track quickly, the early nomenclature for a hard drive was the DASD or DIRECT ACCESS STORAGE DEVICE.

Movement of the read/write head arm takes a little time. For this reason an ACCESS TIME is associated with hard drives and stated in advertising and specification sheets. Generally this time is stated as the AVERAGE ACCESS TIME and is frequently in the thousandths of seconds or millisecond range which is fast indeed. The old IBM XT class machines featured access times around 85 milliseconds with the AT class machines featuring access times around 40 seconds. Newer hard drives post times in the 28 to 15 millisecond access range. Remember, the faster you can move the read/write heads, the faster you can get to your data.

The AVERAGE WAIT TIME is a less frequently discussed number but equally interesting. Once the read/write head is positioned over the track holding your data, the system must wait for the correct sector to pass beneath. Obviously, the average wait time is one half the time it takes for a full rotation of the platter. This figure is rarely given in advertisements and is usually comparable for most drives of the same type and is generally much shorter than the access time. Speed matters to a hard drive! Average wait time is published if you dig it out of the specification sheet or write to the manufacturer.

An extension of this logic brings us to consider the INTERLEAVE FACTOR for a disk. Generally a hard drive reads and writes information in sectors of the same, repeatable size such as 512 bytes. However programs and data files are usually much bigger than this and obviously must be scattered onto many sectors. The problem is that the disk rotation is much too fast for a large file to be written in perfectly contiguous sectors on the same track. If you tried to write the data onto a track, one byte after the next, the central processing unit chip or CPU could not absorb the data fast enough.

The solution is to place sectors to be read in ALTERNATING fashion which gives the CPU time to digest the data. Thus if a circular track on the platter had 8 sectors you might number and read them in this order: 1,5,2,6,3,7,4,8. This way the CPU has a "breather" in between each sector read. The number of rotations it takes the heads to read ALL tracks in succession is the INTERLEAVE FACTOR. Slow CPU chips can force a disk to use an interleave factor of 3 or even 4. A faster processor might be able to handle a disk interleave of 1:2 (such as 80286 processor chips) or even 1:1 (such as 80386 processor chips.) It is possible to low level format a disk and change its interleave factor; but if the CPU cannot keep up, the adjustment is worthless. To the processor operating in millionths of a second, the time drain of waiting for a hard drive which operates in thousandths of a second or floppy drive which operates in tenths and full seconds is wasted time. The obvious point of logic is that when using a hard drive you need to organize files for minimum time delays for the processor.

The first outer track on a disk is always the boot record which loads the main portions of DOS into the machine. Following this is the file allocation table or FAT which we discussed in earlier tutorials. The FAT maintains data in CLUSTERS which, for an XT class machine are 4096 bytes. On the AT class machine the cluster size is 2048 bytes which is much more efficient and less wasteful of disk space. Following the FAT are the sectors for the root directory of the hard drive. Each directory entry is 32 bytes in length. Curiously, and to our good advantage, unused entries in the directory have a unique first character byte. When a file is deleted though DOS, ONLY the first character is reset.

Fortunately this allows various utility programs to attempt to recover the deleted file since ONLY the directory data is altered but NOT the file itself. However, as time goes on and additional files are added to the disk, the original file is overwritten by new information. This is why you need to act immediately if you discover you have accidentally deleted a file. An advantage to the use of the FAT is that files do not have to be given a fixed amount of space on a disk - they can use as many or few clusters as needed. The downside is that the file pieces can be scattered wildly over the surface of the disk in a non contiguous fashion which only the FAT can track. This means more read/write head motion and more wasted time as far as the CPU and the performance of your program is concerned.

Additionally, if you have many deleted files within the directory, DOS must search tediously through each one from top to bottom of the directory to find a match for the file you are trying to locate. Obviously, then, programs and data of high use should have their directory entries located near the top of the directory to speed the search. Each time the read/write head moves takes time: searching the directory and finding the pieces of the scattered file all take movement of the read/write arm. There are several ways to unfragment files which boost disk performance, and we'll talk about those techniques it a bit.



HARD DISKS - STRATEGIES FOR TURBOCHARGED RESULTS


Before we examine methods for improving hard drive performance, several simple "care and feeding" precautions should be mentioned.

Hard drives are touchy if mistreated! Once brought up to speed, a hard drive should never be bumped or moved. The read/write head (similar to the phonograph needle resting on a record) will smash or chip into the surface of the spinning hard drive platter and take your data with it. Either the head or the magnetically coated platter can be permanently damaged. Allow the hard drive to some to a complete stop before moving the computer.

In addition always use a "parking" software package to move the read/write head to the safety zone before turning off the computer. A parking program usually accompanies most computers which have hard drives installed or can be obtained from commercial or shareware sources. A few drives automatically park the heads when turned off but this tends to be a rare feature seen mostly on high priced hard drives.

Always maintain copies of data and programs outside the hard drive by "backing up" onto a floppy or tape. How often should you back up your files? Daily if you use the computer to produce many changes to important documents. Weekly backup is probably a bare minimum considered reasonable for occasional computer users. Other computer users maintain vital data on floppies or other backup systems and use the hard drive to store programs or applications only such as a spreadsheet or database. Backups are a good idea even for floppy disk systems which have no hard drive.

Make two copies of every file regardless of whether you have a hard drive or not. Some shareware and commercial utilities ease the backup chore by only copying those files to a floppy which have been changed or updated since the last backup has been performed. They ignore files which have not changed and thus do not require copying again. This can save a lot of time when backing up valuable files from your hard drive to a floppy for safekeeping.

Hard drives should periodically be reorganized (files unfragmented) to ensure speedy retrieval and access to data. Inexpensive or free software programs known as "disk file unfragmenters" do this job nicely. As disk files are created and deleted, blank spaces and unused sectors begin to build up.

Gradually files are broken into pieces and scattered over the many tracks and sectors of the disk. This happens to both floppies and hard drives, but is especially annoying on hard drives because of the dramatic increase in time it takes to load a program or data file. The File allocation table is the culprit, sense all data is packed away in the first and handiest sector on the drive which the FAT can find.

The FAT allows files to be fragmented down to the cluster level. One way to unfragment a disk is to copy all of the files off to floppies and then recopy them back to the hard drive - a tedious nuisance at best. You would do this with the DOS XCOPY or COPY commands but not DISKCOPY since this would retain the tracks and their fragmentation as you first found them.

Defragmenting programs perform this task without requiring removal of the files from the hard drive. They perform their magic by moving around the clusters of a scattered file in such a way as to reassemble it into contiguous pieces again. Some customization is permitted with the more sophisticated "defragmenting" programs. For example, subdirectory files can be relocated after the root or below a different subdirectory or, in another example, high use files might be placed higher in the directory listing for faster disk access.

The first time a defragmenting program is run may require several hours if a hard drive is large and badly fractured with scattered files and clusters. It is a good idea to backup all essential files prior to "defragging" just in case there is a power failure during a long "defrag". Subsequent runs of the "defragger" produce runs of only a few minutes or so since the heavy work was done earlier. Essentially, "defragging" the hard drive should be done regularaly, perhaps weekly. Defragging is not a substitute for caching, ramdisks, or buffer - instead it is a maintenance function which should be done regularly.

Yet another possible avenue to improve disk performance is that of changing the disk interleave factor which we will discuss a bit later in this tutorial. By way of brief introduction: the disk interleave indicates how many revolutions of the magnetic platter are required to read all the sectors of data from the spinning track. A ratio of 1:1 means all data can be read sequentially. One sector of data after another.

There is some overhead time required for the read/write head to zip to the FAT area of the disk (if it is not in a cache or buffer) to determine location of the next sector along the disk track.

For example, five clusters of data on a track might require four trips back to the FAT track to find the cluster addresses even on a completely defragmented disk. We will talk more about cluster and defragmenting a bit later in this tutorial.

Nevertheless, depending on the speed of your central processor or CPU, using a program which tests and alters the interleave factor, IF THIS CAN BE DONE, may yield better performance. Most interleave adjustment software first performs a test to determine the current interleave, the possible changes and of course how much performance time might be gained. A few of these packages can alter the interleave with the files in place but you should backup truly essential files before starting the process. Interleave factor adjustment are mainly derived from the CPU speed NOT the disk speed. Thus a fast AT or 80386 equipped machine will more likely be able to take advantage of an interleave adjustment.

Tinkering with a hard drive for optimum results might best be divided into two categories: DISK SUBSTITUTION and DISK ALTERATION. DOS allows two clever ways substituting RAM memory for disk memory.

In the first, using BUFFERS, the small CONFIG.SYS file on your hard drive is modified to contain a buffers statement. A sample might be: BUFFERS=20. A DOS buffer is an area of RAM memory capable of holding a 512 byte mirror image of a disk sector. This allows DOS to quickly search the buffer area for frequently used data instead of the slower disk. In the older XT class machine, if you did not specify a buffer size, DOS defaulted to 2 buffers while later versions of DOS default to about 10 buffers. Most users settle on about 20 buffers but you can specify up to 99 with current releases of DOS. But you don't get something for nothing. If you used the full 99 buffers available, you would soak up 45K of your main RAM memory! The downside of using buffers is that more is not necessarily better.

Unfortunately, DOS searches the buffer area of RAM sequentially rather than logically so if DOS requires data which is in the buffer area, it will search each 512 byte area in sequence from top to bottom even though the data it needs may be at the end of the buffer. Logically, then, there is an optimum number of buffers - too many used with a small program and you can slow things down, not enough and DOS will be forced to go out to the disk to retrieve what it needs. If you rarely use the same data within a program twice but load lots of different programs and data, a large number of buffers won't help. However if you need frequent access to a certain data file or portion of that file, buffers will help. Portions of the FAT are kept within the buffers area, so dropping your buffers to zero has the damaging effect that DOS must always go to the disk to read the FAT which isn't helpful either.

Another way of substituting RAM memory for disk memory involves using a RAMDISK. The idea is to create in RAM memory an entire disk or a small portion of a disk. This works like magic on many machines since the reading of tracks and sectors takes place at the high speed of RAM memory rather than the mechanically limited speed of the read/write heads on a floppy or hard drive.

But be careful. Three areas of difficulty can arise. First you must remember to take the data from a floppy or hard drive and move it into the RAMDISK. Many people do this automatically from within an AUTOEXEC.BAT file or may have several floppies, each with a different RAMDISK configuration depending on the task at hand. Copying data to the RAMDISK usually moves along briskly. Secondly you must sacrifice a large area of memory for the RAMDISK which can no longer be used by your main program. Users of computers with extended or expanded memory usually choose to put their RAMDISK in the extended or expanded memory area of RAM so that precious main memory is not lost. Still, a small RAMDISK can soak up 64K of RAM memory and one or two MEG RAMDISKS area common for many users. The third and most serious problem when using RAMDISKS is that they are volatile - switch off the machine or experience a power failure, and your data is lost forever! Rather than residing safely on a magnetic disk, the data is "floating" in RAM memory and should be - MUST BE! - written to a disk before the machine is powered down.

Many applications fly with a RAMDISK. Users of word processors find that moving the spelling checker and thesaurus to the RAMDISK speeds up things considerably since these are used heavily in a random manner. Spreadsheet users find that reading and writing short data files to RAMDISKS is a boon. Programs which use overlay files or temporary files as well as programming compilers benefit from RAMDISK use. Batch files which are disk intensive as well as small utilities really sprint when placed on a RAMDISK. Basically, any program file which is frequently used and loaded/unloaded repeatedly to a disk during normal computer operation is an excellent candidate for RAMDISK placement. DOS contains a RAMDISK which is called by using the statement DEVICE=VDISK.SYS or DEVICE=RAMDRIVE.SYS (if you are using MSDOS) which is placed in your CONFIG.SYS file. Your DOS manual details the specifics such as stating the size of RAMDISK and giving it a drive letter. You must still copy your target files into the RAMDISK and place it in the search path (with the PATH= command) as we mentioned in a previous tutorial. And the RAMDISK should always be the first drive letter mentioned in the path command so that DOS searches it first for optimum results.

Yet another area of investigation is that of CACHE software. Essentially a CACHE is an extension of the buffers idea we discussed earlier. But the twist is that the CACHE is searched intelligently by a searching algorithm within the CACHE software rather than from top to bottom as with the more typical DOS buffer search system. Disk CACHE software can be obtained as either commercial software or shareware. As with a RAMDISK, the CACHE requires a chunk of RAM memory to operate. This can be extended memory, expanded memory or main RAM memory. Some manufacturers include a CACHE program with the software package or DOS disk. A CACHE is a sophisticated type of RAMDISK, in a rough sense.

CACHE software allocates a large area of memory for storage of frequently used disk data. This data is updated by an intelligent CACHE search algorithm in an attempt to "guess" which tracks of a disk you might read or need next. The CACHE also stores the most frequently used disk data and attempts to remove less frequently used data. Whenever DOS requests disk data, the CACHE software first tries to fill the order from data currently stashed in the CACHE which prevents a slower disk search.

When data is written from the program to the CACHE, first a disk write is done to prevent data loss in case of power failure and then the data is stashed in the CACHE in case it is needed again. Usually the hard drive data is the target of the CACHE activity, but a floppy disk could also be cached. All CACHE software allows you to allocate the size of the CACHE as well as the drive or drives to be cached. And some even allow you to specify exact files or data to be cached. The key is that high use data lives in RAM memory which keeps tedious disk access times low. In general, if your computer has a megabyte or more of memory and a speedy processor such as an 80286 or 80386 either or both a CACHE or RAMDISK option does improve performance.

As we leave hard disk boot camp, let's finally look at hard drive formatting processes. Two basic formatting operations are of concern: physical formatting or low level formatting and logical or high level formatting. When you use the format program on a floppy disk both low level and high level formatting is accomplished. On a hard disk, formatting performs only logical or high level formatting. On a hard disk, low level formatting is usually done to a disk before shipment. As an aside, the FDISK command of DOS has little to do with either type of formatting, but is a method of partitioning or arranging the data onto the hard drive tracks. Each disk platter is separated into circular concentric tracks where data is stored as we saw earlier. During physical formatting the tracks are divided into further subdivisions called clusters and further yet into sectors. High level formatting involves the specific ordering of the space for the exclusive use of DOS and is a bit more analogous to the formatting of a floppy disk.

Some software programs of use by hard drive owners:

The following two programs perform low level formatting and simple diagnostic routines on a hard drive:

Disk Manager and CheckIt

Data recovery and "unerasing" programs also containing diagnostic routines are:

PC Tools Deluxe, Norton Utilities, Mace Utilities

Extensive diagnostic and maintenance/data repair functions as well as interleave alteration and head parking are offered by:

SpinRite II, Optune, Disk Technician

Shareware programs with unerase functions include:

Bakers Dozen

Shareware programs with defragmentation capabilities include:

SST and PACKDISK.

Tutorial finished. Be sure to order your FOUR BONUS DISKS which expand this software package with vital tools, updates and additional tutorial material for laptop users!