Comparing the Fast ATA and Enhanced IDE Disk Drive Interfaces
- The introduction of new high-speed microprocessors and local bus architectures for PCs has led to the
development of faster disk drives and other peripheral devices. On hard disk drives, high-speed data transfer
rates are essential to improved PC perf ormance because a computer is only as fast as its slowest component.
- Until recently, the term Enhanced Integrated Drive Electronics (IDE) was used to identify drives with faster
data transfer rates. However, Enhanced IDE means more than that, and the term has often been misused or
- Quantum, Seagate, and numerous other manufacturers in the computer industry have joined together to introduce
Fast AT Attachment (ATA), which represents only the high-speed data transfer rates for ATA hard drives. The term
Fast ATA can be easily identified by computer users when they purchase the fastest peripherals for their notebook
and desktop PC systems.
- Unlike Enhanced IDE, Fast ATA is based on industry standards to help ensure compatibility with older systems and disk drives. Fast ATA data transfer protocols meet the specifications of the Small Form Factor (SFF) Committee's official ATA-2 document.
This Quantum Technical Information Paper (TIP) explains the differences between the Fast ATA and Enhanced IDE interfaces. The paper discusses different implementations of the ATA interface, why Fast ATA is important and Quantum support of both the Fast AT A interface and all Enhanced IDE features.
The most common disk drive interface designed for the PC is the ATA interface, originally known as the IDE interface. The interface was designed specifically for disk drives, and when first introduced, limited disk buffer-to-host data transfer rates to 4.1 megabytes (MB)/second.
Since that time, the ATA industry standards committee has greatly extended the capabilities of the interface to keep pace with other computer industry advancements. The introduction of accelerated data transfer rates was essential to these industry improvements.
In late 1993, a faster ATA interface, made possible by the new local bus architecture, was introduced. In this implementation of the interface, the disk drive is connected directly to the CPU bus, bypassing the expansion bus completely. Therefore, data transfer speeds are limited only by the speed of the local bus and the disk drive itself.
As with the SCSI interface, there are different implementations of the ATA interface: ATA, Fast ATA, and Fast ATA-2. The various SCSI protocols include Fast SCSI-2, Wide SCSI-2, SCSI-3, and others. End users and system designers alike can easily identify with the principal benefit of each ATA and SCSI implementation - faster data transfer rates.
Disk drives that incorporate the Fast ATA standard achieve the high-speed data transfers when the ANSI Standard Programmed Input/ Output (PIO) mode 3 and Multiword Direct Memory Access (DMA) mode 1 protocols are implemented. System and disk drive manufacturers who implement the PIO mode 3 or Multiword DMA mode 1 can transfer data up to a maximum of 11.1 MB/second (PIO mode 3) or 13.3 MB/second (DMA mode 1). System designers choose the protocol they want to support.
Fast ATA-2 refers to both the new PIO mode 4 and Multiword DMA mode 2 protocols (not yet available on systems). System and disk drive manufacturers who implement PIO mode 4 or Multiword DMA mode 2 will be able to transfer data up to a maximum 16.6 MB/second (both PIO mode 4 and DMA mode 2 have the same maximum data transfer rate). With Fast ATA-2, system designers will also choose the protocol they want to support.
Fast ATA and Fast ATA-2 are based on industry standards to help ensure compatibility with older systems and disk drives. The data transfer protocols meet the specifications of the SFF Committee's official ATA-2 document (Ref: 9048D), which has been submitted to ANSI for approval.
Faster data transfer rates are important because a computer is only as fast as its slowest component. Today's 486, Pentium, and PowerPC-based computers offer processor speeds many times faster than only two years ago. Bus speeds have also increased with the inclusion of 32-bit VL and PCI local buses, which have a maximum data transfer
rate of 132 MB/second.
Faster buses mean that data can be transferred from the storage device to the host at greater speeds. Fast ATA and Fast ATA-2 allow disk drives to store and access this data faster, thus enhancing the other high-speed components in the system and removing the bottleneck associated with older ATA/IDE drives. In short, Fast ATA helps bring very high performance to desktop PC systems.
In addition, when compared to SCSI, Fast ATA is the least expensive way to achieve faster disk drive data transfer rates and higher system performance. The implementation of Fast ATA through system BIOS provides performance without incremental hardware co sts. Older systems can support Fast ATA using an inexpensive host adapter.
Fast ATA and Fast ATA-2 are easy to implement in either VL or PCI local bus systems. The hardware connection can be made using a standard 40-pin ATA ribbon cable from the drive to the host adapter. Direct connection to the motherboard further eases integration when provided by the motherboard supplier.
Once connected, the high data transfer capabilities of Fast ATA can be enabled through the data transfer options found in most CMOS BIOS setup tables. Newer versions of BIOS provide automatic configuration for Fast ATA drives.
Fast ATA can improve efficiency by allowing more work to be completed in less time because the computer moves data faster. Graphic, multimedia, and audio/visual software users will benefit most because the speed of those applications, which work with large blocks of data, are transfer-rate dependent.
The Fast ATA and Enhanced IDE interfaces both use the local bus to speed data transfer rates. Enhanced IDE also uses the same PIO modes as Fast ATA, although a data transfer rate equal to the PIO mode 4 rate has not been announced for Enhanced IDE. The major differences between Fast ATA and Enhanced IDE are that the latter includes three distinct features in addition to fast data transfer rates. The additional features of Enhanced IDE are as follows:
- High-capacity addressing of ATA hard drives over 528 MB - a BIOS and device driver function
- Dual ATA host adapters supporting up to four hard disk drives per computer system - a function of BIOS, operating system, and host adapter, not the drive
- Support for non-hard disk drive peripherals such as CD-ROMs - a function of BIOS and the operating system, not the drive
Each of these features supports improved functionality at a system level, a positive development for the industry and end users. However, support for all three features requires an extremely high degree of integration and revisions to operating systems and hardware, in addition to BIOS changes. Specific support is required not only for the storage peripherals but also for host adapters, core logic, the system bus, BIOS, and operating systems
- virtually every major block of PC architecture.
There is no central industry-supported standard that controls the features of Enhanced IDE. With no standard, some products sold as "Enhanced" may provide only one of the three features of Enhanced IDE. For example, fast data transfer rate support is be coming standard on mid-range and high-end local bus systems. This single feature could satisfy the users immediate requirements without the need for the other features of Enhanced IDE.
In the future, if the same system is upgraded to add the remaining features of Enhanced IDE, users may be forced to purchase an Enhanced IDE package that contains a feature already installed. This could result in unnecessary costs, integration conflicts, and incompatibility with original factory implementations.
Fast ATA, on the other hand, represents only the fast data transfer rates for ATA hard drives (support for PIO mode 3 or 4 and DMA mode 1 or 2). Fast ATA and Fast ATA-2 data transfer rates can be easily achieved when the system BIOS and hard drive suppo rt the PIO and DMA protocols.
BIOS that supports Fast ATA does not necessarily support high- capacity addressing, dual host adapters or non-hard drive peripherals. But these features are being introduced independently by system manufacturers in order to compete in the PC marketplace.
All of Quantum's disk drives designed for PCs now support Fast ATA, and new products with Fast ATA support will be introduced in early 1995. The drives are also fully backward compatible with older ATA/IDE (non-Fast ATA) BIOS.
The Quantum drives support both the Extended CHS (Cylinder Head Sector) and LBA (Logical Block Address) addressing methods in overcoming the 528 MB DOS capacity barrier. Quantum drives can also be used with dual host adapters. Finally, there are no incompatibilities with Quantum hard drives that would prevent computer systems from supporting non-hard drive peripherals.
Quantum drives that support Fast ATA include the following families:
- Quantum ProDrive LPS 170/210/340/420
- Quantum ProDrive LPS 270/540
- Quantum Maverick 270/540
- Quantum Lightning 365/540/730
- Quantum Daytona 127/170/256/341/514
Fast ATA and Fast ATA-2 are important technologies that can take advantage of the performance provided by the latest high-speed microprocessors and bus architectures. The high-speed interfaces are based on industry standard specifications and are the least expensive way to achieve faster disk drive data transfer rates. Fast ATA is not a group of features that requires an extremely high level of integration, and only represents the fast data transfer rates for ATA hard drives (PIO mode 3 or 4 and DMA mode 1 or 2).