Tandy 1000HD Hard Disk SpeedUp

The 5 1/4th inch 10 megabyte Tandon Hard Disk Drive that comes standard on the Tandy 1000HD is a durable piece of equipment, though not the fastest. Using the Core Hard Disk Performance Test version 2.7, the drive (hard sectored by the program HSECT.COM on the Tandy HARD DISK UTILITIES disk supplied with the machine) and running PC DOS 3.2, reveals the following:

               Data Transfer Rate = 100 kilobytes/sec
                Average seek time = 97 msec
           Average track to track = 17 msec

While nothing can be done about the last two figures (hardware dependent), the data transfer rate can be optimized to 125 KB/sec, a 25% improvement by optimizing the interleave factor (software dependent) when hard formatting the disk.

Alter the interleave factor, you may ask? Yes, the Western Digital Controller Board as supplied with the Tandy 1000HD has a formatting program in ROM, which is slightly different from those WDC controller boards supplied by third party vendors. Through trial and error, I found that using an interleave factor of 4 optimized disk performance, obtaining the following results:

                    Data Transfer Rate             Interleave Factor
                          28.4                             1
                          27.1                             2
                          28.5                             3
                         124.6                             4
                         100.5                             5
                          83.6                             6
                          72.0                             7

It appears that the HSECT.COM program uses an interleave factor of 5. To reformat your hard disk, follow these instructions:

       1. Make a backup copy of all files on your Hard Disk--they will be
          destroyed by this procedure.

       2. Type "debug" at the DOS prompt, then type:

          -r ax <cr>
          AX 0000
          :0004 <cr>     {Enter the value of 0004 into register AX}

          -g=C800:05     {Execute Code beginning at address C800:0005.

          You will then be prompted to answer (y)es or (n)o to hard sector
          format the Disk Drive using an interleave factor of 4.  Type "y".
          Upon completion of the task, you will be returned to the DOS prompt.

       3. Now simply reformat the hard disk using HFORMAT (MS-DOS 2.11.22)
          or the FORMAT command of PC-DOS 2.10 or higher.

It is to your advantage to use PC-DOS 3.1 or 3.2. Using the DOS31.PAT and DOS32.PAT files found in the IBM Sig Data Libraries, you can modify your 10 megabyte disk drive into clusters of 2048 bytes (4 sectors). PC and MS-DOS below 3.0 formats all disks into 4096 byte clusters (8 sectors). DOS 3.0,3.1 and 3.2 format 19 megabyte or smaller drives with 8 sector clusters, and larger drives with 4 sector clusters. By modifying the boot record on sector 0 track 0 as outlined in the DOS3x.PAT files, you can fool DOS (3.1 or 3.2 only !) into using the smaller sector cluster allocations. The advantage is an average saving of 10-15% of disk space that would otherwise be wasted on smaller file sizes. This is the result of using 16 bit entries in the File Allocation Table, instead of the usual 12 bit numbers. As a specific example, if you have a 760 byte file, DOS allocates 4096 byte (8 sectors) of disk space to that file when using the 12bit FAT entry, versus 2048 byte (4 sectors) with the 16 bit FAT entry.

I can only verify the speed results using PC-DOS 3.2 on the Tandy 1000HD.

I will be comparing MS-DOS 2.11.22, MS-DOS 3.1, and PC-DOS 3.1 to determine possible differences in speed between operating systems and whether the interleave factor is independent of them.