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 (http://www.t13.org) and is responsible for all standards relating to the parallel and Serial AT Attachment 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 (http://www.serialata.org) was formed to initially create the Serial ATA 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 they 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 or Global Engineering Documents (see the Vendor List on the disc that accompanies this book). Draft versions of the standards can be downloaded from the T13 Committee or Serial ATA International Organization (SATA-IO) website. The parallel ATA interface has evolved into several successive standard versions, introduced as follows:
Since ATA-1, newer versions of the ATA interface and complementary BIOS support larger and faster drives, as well as different types of devices other than hard disks. ATA-2 and later have improved the original ATA interface in five main areas:
Each newer version of ATA is backward-compatible with the previous versions. In other words, older ATA-1 or ATA-2 devices work fine on ATA-6 and ATA-8 interfaces. ATA-7 and ATA-8 include both parallel and Serial ATA. 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 all the ATA versions in more detail.
ATA-1 (AT Attachment Interface for Disk Drives)ATA-1 defined the original AT Attachment 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:
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 (228220 = 267,386,880 sectors), it did not address BIOS limitations that stopped at 528MB (1024x16x63 = 1,032,192 sectors). The BIOS limitations would be addressed in subsequent ATA versions because, at the time, no drives larger than 528MB had existed. ATA-2 (AT Attachment Interface with Extensions-2)ATA-2 first appeared in 1993 and 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 as compared to the original ATA standard include
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 (AT Attachment Interface-3)First appearing in 1995, 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:
ATA-3 built on ATA-2, adding improved reliability, especially of the faster PIO mode 4 transfers; however, ATA-3 did not define any faster modes. ATA-3 did add a simple password-based security scheme, more sophisticated power management, and SMART. This enables a drive to keep track of problems that might result in a failure and therefore avoid data loss. SMART is a reliability prediction technology that was initially developed by IBM. 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 (AT Attachment with Packet Interface Extension-4)First appearing in 1996, 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. The major revisions added in ATA-4 were as follows:
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 during 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.
ATA-4 made ATAPI support a full part of the ATA standard, and thus 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 bandwidthtwice 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. Many hard drives purchased in retail kits include the 80-conductor cable, although other types of devices, such as optical drives, include only a 40-conductor cable. Support for a reserved area on the drive called the host protected area (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, which is similar to that provided in SCSI-2. This enabled better multitasking as multiple programs make requests for ATA transfers. Another standard approved by the T13 committee in 1998 is "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 has enabled vendors such as Maxtor, Western Digital, and others 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.
ATA/ATAPI-5 (AT Attachment with Packet Interface-5)ATA-5 first appeared in 1998 and 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 has now been made mandatory for drives running in UDMA/66 or faster modes. This cable was first announced in ATA-4 but became mandatory in ATA-5 to support the Ultra-ATA/66 mode. 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, nonUltra-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:
The 40-pin, 80-conductor cables will 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 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 or later, Windows 98/Me, and Windows 2000/XP 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 (AT Attachment with Packet Interface-6)ATA-6 began development during 2000 and 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:
Besides adding the 100MBps UDMA Mode 5 transfer rate, ATA-6 also 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" drives exceeding 137GB were introduced during 2001, but they were originally available only in SCSI versions because SCSI doesn't share 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 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 (AT Attachment 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 previous standard (ATA-6), with some additions. The primary additions to ATA-7 include
Note that although the throughput has been increased from the drive controller (on the drive) to the motherboard via the UDMA modes, most ATA driveseven those capable of UDMA Mode 6 (133MBps) from the drive to the motherboardstill have an average maximum sustained transfer rate while reading data of under 60MBps. This means that although newer ATA drives can transfer at speeds up to 133MBps from the circuit board on the drive to the motherboard, data from the drive media (platters) through the heads to the circuit board on the drive moves at less than half that rate. For that reason, running a drive capable of UDMA Mode 6 (133MBps) on a motherboard capable of only UDMA Mode 5 (100MBps) really doesn't slow things down much, if at all. Likewise, upgrading your ATA host adapter from one that does 100MBps to one that can do 133MBps won't help much if your drive reads data off the disk platters at only half that speed. Always remember that the media transfer rate is far more important than the interface transfer rate when selecting a drive because the media transfer rate is the limiting factor. The ATA/133 transfer mode was actually proposed by Maxtor, and only a few other drive manufacturers have adopted it since. Among them, VIA, ALi, and SiS have added ATA/133 support to their latest chipsets, but Intel has decided to skip ATA/133 in its chipsets in lieu of adding Serial ATA (150MBps or 300MBps) instead. This means the majority of current systems do not have support for ATA/133; however, all ATA/133 drives will work in ATA/100 mode as well. As a historical note, ATA-7 is the last revision of the venerable parallel ATA standard. ATA is evolving into Serial ATA, which was incorporated into the ATA-7 specification and is covered in detail later in this chapter. SATA/ATAPI-8In 2004, work began on SATA-8, which is a new ATA standard based on ATA-7 that will carry forward the development of Serial ATA while still including parallel ATA. The main features of ATA-8 include
As the development of ATA-8 progresses, it is expected that newer features designed by the SATA-IO committee will be incorporated, including the faster SATA 3Gbps transfer speed. It is also expected that ATA-8 will be finalized and officially published in 2006. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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