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This chapter is from the book

ATA Standards

Today, the ATA interface is controlled by an independent group of representatives from major PC, drive, and component manufacturers. This group is called Technical Committee T13 (www.t13.org) and is responsible for all standards relating to the Parallel and Serial ATA storage interfaces. T13 is a part of the International Committee on Information Technology Standards (INCITS), which operates under rules approved by the American National Standards Institute (ANSI), a governing body that sets rules that control nonproprietary standards in the computer industry as well as many other industries. A second group called the Serial ATA International Organization (www.serialata.org) was formed to initially create the SATA standards, which are then passed on to the T13 Committee for refinement and official publication under ANSI. The ATA-7 and ATA-8 standards incorporate both parallel and serial interfaces.

The rules these committees operate under are designed to ensure that voluntary industry standards are developed by the consensus of people and organizations in the affected industry. INCITS specifically develops information processing system standards, whereas ANSI approves the process under which these standards are developed and then publishes them. Because T13 is essentially a public organization, all the working drafts, discussions, and meetings of T13 are open for all to see.

Copies of any of the published standards can be purchased from ANSI (www.ansi.org) or the IHS Standards Store (formerly Global Engineering Documents, http://global.ihs.com). Draft versions of the standards can be downloaded from the T13 Committee or Serial ATA International Organization (SATA-IO) website.

Each newer version of ATA is backward compatible with the previous versions. In other words, older ATA-1 and ATA-2 devices work fine on ATA-7 and ATA-8 interfaces. ATA-7 and ATA-8 include both PATA and SATA. Newer versions of ATA are normally built on older versions, and with few exceptions can be thought of as extensions of the previous versions. This means that ATA-8, for example, is generally considered equal to ATA-7 with the addition of some features.

Table 7.2 breaks down the various ATA standards. The following sections describe recent ATA versions in more detail.

Table 7.2. ATA Standards





PIO Modes

DMA Modes

UDMA Modes

Parallel Speed (MBps)

Serial Speed (MBps)









Drives support up to 136.9GB; BIOS issues not addressed.








Faster PIO modes; CHS/LBA BIOS translation defined up to 8.4GB; PC-Card.








S.M.A.R.T.; improved signal integrity; LBA support mandatory; eliminated single-word DMA modes.









Ultra-DMA modes; ATAPI Packet Interface; BIOS support up to 136.9GB.








Faster UDMA modes; 80-pin cable with auto-detection.








100MBps UDMA mode; extended drive and BIOS support up to 144PB.









133MBps UDMA mode; SATA.








Minor revisions for PATA, includes SATA 2.x and 3.x.

S.M.A.R.T. = Self-Monitoring, Analysis, and Reporting Technology

ATAPI = AT Attachment Packet Interface

MB = Megabyte; million bytes

GB = Gigabyte; billion bytes

PB = Petabyte; quadrillion bytes

CHS = Cylinder, Head, Sector

LBA = Logical block address

PIO = Programmed I/O

DMA = direct memory access

UDMA = Ultra DMA (direct memory access)

ATA-1 (ATA Interface for Disk Drives)

ATA-1 defined the original ATA interface, which was an integrated bus interface between disk drives and host systems based on the ISA (AT) bus. These major features were introduced and documented in the ATA-1 specification:

  • 40/44-pin connectors and cabling
  • Master/slave or cable select drive configuration options
  • Signal timing for basic Programmed I/O (PIO) and direct memory access (DMA) modes
  • Cylinder, head, sector (CHS) and logical block address (LBA) drive parameter translations supporting drive capacities up to 228–220 (267,386,880) sectors, or 136.9GB

Although ATA-1 had been in use since 1986, work on turning it into an official standard began in 1988 under the Common Access Method (CAM) committee. The ATA-1 standard was finished and officially published in 1994 as “ANSI X3.221-1994, AT Attachment Interface for Disk Drives.” ATA-1 was officially withdrawn as a standard on August 6, 1999.

Although ATA-1 supported theoretical drive capacities up to 136.9GB (228–220 = 267,386,880 sectors), it did not address BIOS limitations that stopped at 528MB (1024 × 16 × 63 = 1,032,192 sectors). The BIOS limitations would be addressed in subsequent ATA versions because, at the time, no drives larger than 528MB existed.

ATA-2 (ATA Interface with Extensions-2)

ATA-2 was a major upgrade to the original ATA standard. Perhaps the biggest change was almost a philosophical one. ATA-2 was updated to define an interface between host systems and storage devices in general and not only disk drives. The major features added to ATA-2 compared to the original ATA standard include the following:

  • Faster PIO and DMA transfer modes
  • Support for power management
  • Support for removable devices
  • PCMCIA (PC Card) device support
  • Identify Drive command that reports more information
  • Defined standard CHS/LBA translation methods for drives up to 8.4GB in capacity

The most important additions in ATA-2 were the support for faster PIO and DMA modes, as well as methods to enable BIOS support up to 8.4GB. The BIOS support was necessary because although ATA-1 was designed to support drives of up to 136.9GB in capacity, the PC BIOS could originally handle drives of up to 528MB. Adding parameter-translation capability now allowed the BIOS to handle drives up to 8.4GB. This is discussed in more detail later in this chapter.

ATA-2 also featured improvements in the Identify Drive command that enabled a drive to tell the software exactly what its characteristics are; this is essential for both Plug and Play (PnP) and compatibility with future revisions of the standard.

ATA-2 was also known by unofficial marketing terms, such as Fast-ATA or Fast-ATA-2 (Seagate/Quantum) and EIDE (Enhanced IDE, Western Digital).

Although work on ATA-2 began in 1993, the standard was not officially published until 1996 as “ANSI X3.279-1996 AT Attachment Interface with Extensions.” ATA-2 was officially withdrawn in 2001.

ATA-3 (ATA Interface-3)

ATA-3 was a comparatively minor revision to the ATA-2 standard that preceded it. It consisted of a general cleanup of the specification and had mostly minor clarifications and revisions. The most major changes included the following:

  • Eliminated single-word (8-bit) DMA transfer protocols
  • Added S.M.A.R.T. (Self-Monitoring, Analysis, and Reporting Technology) support for prediction of device performance degradation
  • Made LBA mode support mandatory (previously, it had been optional)
  • Added ATA Security mode, allowing password protection for device access
  • Provided recommendations for source and receiver bus termination to solve noise issues at higher transfer speeds

ATA-3 built on ATA-2, adding improved reliability, especially of the faster PIO mode 4 transfers; however, ATA-3 did not define faster modes. ATA-3 did add a simple password-based security scheme, more sophisticated power management, and S.M.A.R.T. This enables a drive to keep track of problems that might result in a failure and thus avoid data loss. S.M.A.R.T. is a reliability prediction technology that IBM initially developed.

Work on ATA-3 began in 1995, and the standard was finished and officially published in 1997 as “ANSI X3.298-1997, AT Attachment 3 Interface.” ATA-3 was officially withdrawn in 2002.

ATA/ATAPI-4 (ATA with Packet Interface Extension-4)

ATA-4 included several important additions to the standard. It included the Packet Command feature known as the AT Attachment Packet Interface (ATAPI), which allowed devices such as CD-ROM and CD-RW drives, LS-120 SuperDisk floppy drives, Zip drives, tape drives, and other types of storage devices to be attached through a common interface. Until ATA-4 came out, ATAPI was a separately published standard. ATA-4 also added the 33MB per second (MBps) transfer mode known as Ultra-DMA or Ultra-ATA. ATA-4 is backward compatible with ATA-3 and earlier definitions of the ATAPI.

Work on ATA-4 began in 1996, and the standard was finished and officially published in 1998 as “ANSI NCITS 317-1998, AT Attachment - 4 with Packet Interface Extension.” ATA-4 was officially withdrawn in 2012.

The major revisions added in ATA-4 were as follows:

  • Ultra-DMA (UDMA)or Ultra-ATA/33) transfer modes up to Mode 2, which is 33MBps (called UDMA/33 or Ultra-ATA/33)
  • Integral ATAPI support
  • Advanced power management support
  • An optional 80-conductor, 40-pin cable defined for improved noise resistance
  • Host protected area (HPA) support
  • Compact Flash Adapter (CFA) support
  • Enhanced BIOS support for drives over 9.4ZB (zettabytes or trillion gigabytes) in size (even though ATA was still limited to 136.9GB)

The speed and level of ATA support in your system is mainly dictated by your motherboard chipset. Most motherboard chipsets come with a component called either a South Bridge or an I/O Controller Hub that provides the ATA interface (as well as other functions) in the system. Check the specifications for your motherboard or chipset to see whether yours supports the faster ATA/33, ATA/66, ATA/100, or ATA/133 mode. One indication is to enter the BIOS Setup, put the hard disk on manual parameter settings (user defined), and see which (if any) Ultra-DMA modes are listed. Most boards built in 1998 support ATA/33. In 2000 they began to support ATA/66, and by late 2000 most started supporting ATA/100. ATA/133 support became widespread in mid-2002.

left-arrow.jpg See the Chapter 4 section, “Chipsets,” p. 181.

ATA-4 made ATAPI support a full part of the ATA standard; therefore, ATAPI was no longer an auxiliary interface to ATA but merged completely within it. Thus, ATA-4 promoted ATA for use as an interface for many other types of devices. ATA-4 also added support for new Ultra-DMA modes (also called Ultra-ATA) for even faster data transfer. The highest-performance mode, called UDMA/33, had 33MBps bandwidth—twice that of the fastest programmed I/O mode or DMA mode previously supported. In addition to the higher transfer rate, because UDMA modes relieve the load on the processor, further performance gains were realized.

An optional 80-conductor cable (with cable select) is defined for UDMA/33 transfers. Although this cable was originally defined as optional, it would later be required for the faster ATA/66, ATA/100, and ATA/133 modes in ATA-5 and later.

Support for a reserved area on the drive called the HPA was added via an optional SET MAX ADDRESS command. This enables an area of the drive to be reserved for recovery software.

Also included was support for queuing commands, similar to those provided in SCSI-2. This enabled better multitasking as multiple programs request ATA transfers.

Another standard approved by the T13 committee in 1998 was “ANSI NCITS 316-1998 1394 to AT Attachment - Tailgate,” which is a bridge protocol between the IEEE 1394 (i.LINK/FireWire) bus and ATA that enables ATA drives to be adapted to FireWire. A tailgate is an adapter device (basically a small circuit board) that converts IEEE 1394 (i.LINK or FireWire) to ATA, essentially allowing ATA drives to be plugged into a FireWire bus. This enabled vendors to quickly develop IEEE 1394 (FireWire) external drives for backup and high-capacity removable data storage. Inside almost any external FireWire drive enclosure you will find the tailgate device and a standard ATA drive.

righ-arrow.jpg See the Chapter 14 section, “IEEE 1394 (FireWire or i.LINK),” p. 718.

ATA/ATAPI-5 (ATA with Packet Interface-5)

ATA-5 was built on the previous ATA-4 interface. ATA-5 includes Ultra-ATA/66 (also called Ultra-DMA or UDMA/66), which doubles the Ultra-ATA burst transfer rate by reducing setup times and increasing the clock rate. The faster clock rate increases interference, which causes problems with the standard 40-pin cable used by ATA and Ultra-ATA. To eliminate noise and interference, the newer 40-pin, 80-conductor cable was made mandatory for drives running in UDMA/66 or faster modes. This cable adds 40 additional ground lines between each of the original 40 ground and signal lines, which helps shield the signals from interference. Note that this cable works with older, non-Ultra-ATA devices as well because it still has the same 40-pin connectors.

Work on ATA-5 began in 1998, and the standard was finished and officially published in 2000 as “ANSI NCITS 340-2000, AT Attachment - 5 with Packet Interface.”

The major additions in the ATA-5 standard include the following:

  • Ultra-DMA (UDMA) transfer modes up to Mode 4, which is 66MBps (called UDMA/66 or Ultra-ATA/66).
  • The 80-conductor cable now mandatory for UDMA/66 operation.
  • Automatic detection of 40- or 80-conductor cables.
  • UDMA modes faster than UDMA/33 enabled only if an 80-conductor cable is detected.

The 40-pin, 80-conductor cables support the cable select feature and have color-coded connectors. The blue (end) connector should be connected to the ATA host interface (usually the motherboard). The black (opposite end) connector is known as the master position, which is where the primary drive plugs in. The gray (middle) connector is for slave devices.

To use either the UDMA/33 or the UDMA/66 mode, your ATA interface, drive, BIOS, and cable must be capable of supporting the mode you want to use. The operating system also must be capable of handling direct memory access. Windows 95 OSR2 and later versions are ready out of the box, but older versions of Windows 95 and NT (prior to Service Pack 3) require additional or updated drivers to fully exploit these faster modes. Contact the motherboard or system vendor for the latest drivers.

For reliability, Ultra-DMA modes incorporate an error-detection mechanism known as cyclical redundancy checking (CRC). CRC is an algorithm that calculates a checksum used to detect errors in a stream of data. Both the host (controller) and the drive calculate a CRC value for each Ultra-DMA transfer. After the data is sent, the drive calculates a CRC value, and this is compared to the original host CRC value. If a difference is reported, the host might be required to select a slower transfer mode and retry the original request for data.

ATA/ATAPI-6 (ATA with Packet Interface-6)

ATA-6 includes Ultra-ATA/100 (also called Ultra-DMA or UDMA/100), which increases the Ultra-ATA burst transfer rate by reducing setup times and increasing the clock rate. As with ATA-5, the faster modes require the improved 80-conductor cable. Using the ATA/100 mode requires both a drive and motherboard interface that supports that mode.

Work on ATA-6 began in 2000, and the standard was finished and officially published in 2002 as “ANSI NCITS 361-2002, AT Attachment - 6 with Packet Interface.”

The major changes or additions in the standard include the following:

  • Ultra-DMA (UDMA) Mode 5 added, which allows 100MBps (called UDMA/100, Ultra-ATA/100, or just ATA/100) transfers.
  • Sector count per command increased from 8 bits (256 sectors, or 131KB) to 16 bits (65,536 sectors, or 33.5MB), allowing larger files to be transferred more efficiently.
  • LBA addressing extended from 228 to 248 (281,474,976,710,656) sectors, supporting drives up to 144.12PB (petabytes = quadrillion bytes). This feature is often referred to as 48-bit LBA or greater than 137GB support by vendors; Maxtor referred to this feature as Big Drive.
  • CHS addressing was made obsolete; drives must use 28-bit or 48-bit LBA addressing only.

Besides adding the 100MBps UDMA Mode 5 transfer rate, ATA-6 extended drive capacity greatly, and just in time. ATA-5 and earlier standards supported drives of up to only 137GB in capacity, which became a limitation as larger drives were becoming available. Commercially available 3 1/2-inch drives exceeding 137GB were introduced in 2001, but they were originally available only in SCSI versions because SCSI doesn’t have the same limitations as ATA. With ATA-6, the sector addressing limit has been extended from 228 sectors to 248 sectors. What this means is that LBA addressing previously could use only 28-bit numbers, but with ATA-6, LBA addressing can use larger 48-bit numbers if necessary. With 512 bytes per sector, this raises the maximum supported drive capacity to 144.12PB. That is equal to more than 144.12 quadrillion bytes! Note that the 48-bit addressing is optional and necessary only for drives larger than 137GB. Drives 137GB or smaller can use either 28-bit or 48-bit addressing.

ATA/ATAPI-7 (ATA with Packet Interface-7)

Work on ATA-7, which began late in 2001, was completed and officially published in 2004. As with the previous ATA standards, ATA-7 is built on the standard that preceded it (ATA-6), with some additions.

The primary additions to ATA-7 include the following:

  • Ultra-DMA (UDMA) Mode 6 was added. This allows for 133MBps transfers (called UDMA/133, Ultra-ATA/133, or just ATA/133). As with UDMA Mode 5 (100MBps) and UDMA Mode 4 (66MBps), the use of an 80-conductor cable is required.
  • Added support for long physical sectors. This allows a device to be formatted so that there are multiple logical sectors per physical sector. Each physical sector stores an ECC field, so long physical sectors allow increased format efficiency with fewer ECC bytes used overall.
  • Added support for long logical sectors. This enables additional data bytes to be used per sector (520 or 528 bytes instead of 512 bytes) for server applications. Devices using long logical sectors are not backward compatible with devices or applications that use 512-byte sectors, such as standard desktop and laptop systems.
  • SATA 1.0 incorporated as part of the ATA-7 standard. This includes the SATA physical interconnection as well as the related features and commands.
  • The ATA-7 document split into three volumes. Volume 1 covers the command set and logical registers, which apply to both Serial and Parallel ATA. Volume 2 covers the parallel transport protocols and interconnects (PATA), and Volume 3 covers the serial transport protocols and interconnects (SATA).

The ATA/133 transfer mode was originally proposed by Maxtor, and only a few other drive and chipset manufacturers adopted it. Among the chipset manufacturers, VIA, ALi, and SiS added ATA/133 support to their chipsets, prior to moving on to SATA, but Intel decided from the outset to skip ATA/133 in its chipsets in lieu of adding SATA (150MBps or 300MBps). This means the majority of systems that utilize PATA do not support ATA/133; however, all ATA/133 drives do work in ATA/100 mode.


Work on ATA-8 began in 2004, and some initial parts of the standard were published in 2006 and 2008. Other parts are still in progress and continue to be revised as of 2013. As with the previous ATA standards, ATA-8 is built on the standard that preceded it, with some additions. As with the previous version, ATA-8 includes SATA but adds the newer 2.x and 3.x versions of the SATA specification.

The primary features added to ATA-8 include the following:

  • The inclusion of SATA 2.x and 3.x for serial transport (physical) and command set functions
  • The replacement of read long/write long functions
  • Improved HPA management via additional HPA-related commands
  • Defined IDENTIFY DEVICE word 217 to report drive rotational speed (rpm), where a value of 1 indicates nonrotating media (solid-state drive)
  • Addition of the TRIM command for flash-based solid-state drives (SSDs). This allows the system to inform an SSD which blocks are no longer in use so they can be erased in preparation for future writes

As the development of ATA progresses, it is expected that newer features designed by the SATA-IO committee will be incorporated.

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