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The ATA Specifications

Materials:
Working complete PC
Blank Diskette
Student Diskette, "New Boot A Ver 2.0+"
Student CD-ROM, "Room 6359"
Objectives:
The student will become familiar with the evolution of the hard drive interface technologies,
The student will learn about early proprietary solutions,
and the early XT IDE interface,
and the modern Universal ATA/IDE interfaces,
and the current industry standard SATA interfaces. Competency:
The student will understand the nature and function of the original physical hard drive controllers and their interfaces to the system standard expansion buses. The student will learn about the various proprietary evolutionary technolgies designed to allow interchangeability and upgrade of hard drives up to and including the parallel ATA specifications and the modern Serial ATA interfaces.

ATA Specification Highlights

  1. These controllers are at the other end of the standard 40-pin IDE or 80-wire/40-pin UDMA cables from the hard drives. There has been a steady evolution in the power, speed, and capabilities of the ATA controllers that has kept pace with the incredible pace of advancement in the HDD.

  2. Below is a listing of the ATA controllers, their features, capabilities, performance, and Intel south bridge chipsets in which they can be found:

    Controller  PIO  UDMA  Transfer Rate   Chipset Features Introduced
    ATA-10-2 - 8.33MB/secSIOFirst IDE controller, defined cables, signalling, master/slave IDs, and the first IDE language. No formal support for translations resulted in the 504MB HDD size limit.
    ATA-20-4 - 16.67MB/secPIIXTranslations formally defined, introduced support for PCMCIA, APM, improved (E)IDE language. Formally defined the secondary EIDE controller.
    ATA-30-4 - 16.67MB/secPIIX3SMART, improved signalling including autotermination, LBA mandatory.
    ATA-40-40-233.33MB/secPIIX4Introduced UDMA and optional 80-wire cable, EDD 3.0 BIOS support introduced, integrated ATAPI support. Also part of the PIIX4E and ICH0 chipsets
    ATA-50-40-466.67MB/secICH80-wire UDMA cable autodetection mandatory, UDMA modes 3 and up require the cable. Introduced UDMA mode 4.
    ATA-60-40-5100MB/secICH2Introduced UDMA mode 5, new 48-bit LBA mode defined
    ATA-70-40-6133MB/secICH2Introduced UDMA mode 6
    SATA-I0-40-6150MB/secICH2Introduced Serial ATA physical signalling and 150MB/sec transfer rate, fully ATA-7 backward compatible
    SATA-II0-40-6300MB/secICH2Introduced SATA physical signalling at 300MB/sec transfer rate, fully ATA-7 backward compatible

  3. The major improvements in this series are between the ATA-1 controller and the ATA-2 controllers in which the IDE language was vastly expanded and the secondary controller was officially defined.

  4. Another huge improvement occurred in the step from the ATA-2 controller to the ATA-3 controller in which the devices are expected to have superior capabilities of autoterminating on the IDE bus and the signal timing, waveforms, and integrity at the electronics level was vastly improved as well. The ATA-3 controller was also capable of handling each device individually at its maximum performance rather than locking the controller to the speed of the slowest device. The legend of keeping optical drives on the second controller and not attached to the same controller as the hard drive is no longer necessary because of this improvement (although it still makes some sense since a large data transfer from the optical drive will still bog down the entire channel regardless).

  5. The step between ATA-3 and ATA-4 controllers was probably the largest functional improvement that the end user would notice by integrating ATAPI support including the "El Torito" specification which defined the files and their contents for making bootable CD-ROMs (as well as any other technology using ATAPI including Iomega ZipTM Drives). This carries over into this controller so that it is capable of looking for these files and launching an OS if they are present and in the correct format. This controller also introduced the UDMA controller which functions similarly to the old AT DMA chip but with vastly superior performance.

  6. UDMA was developed for the ATA controllers to improve performance in transfering data with the hard drives. The ATA controller incorporated in the motherboard chipset is manufactured using high end techniques and boasts very high performance. As a result it was given the power to lock the PCI bus and perform data transfers between drives and the memory itself; a technique natively supported in the PCI bus called "bus mastering." The UDMA controller was inspired by the classic AT DMA controller chips that are a stanmdard part of the AT motherboard architecture. However, the UDMA chip supports much faster transfer rates and is incorporated directly into the ATA controller's design and it therefore canoot be used by any other device. All data transfers continue to be 16-bit because this is the data width of the 40-pin (80-wire) IDE cable. However, UDMA modes are given in their transfer rates:
    UDMA ModeControllersTransfer Rate
    0ATA-4 and up16.67MB/sec
    1ATA-4 +25MB/sec
    2ATA-4 +33.33MB/sec
    3ATA-5 +44.44MB/sec
    4ATA-5 +66.67MB/sec
    5ATA-6 + 100MB/sec
    6ATA-7133.33MB/sec

  7. UDMA mode 2 devices may be called UltraATA-33 or just ATA-33 as well as UDMA33 on OEM packaging. The controllers ATA-5 and up must autodetect the UDMA cable in order to enable UDMA mode transfers above UDMA Mode 2.


    Standard 40-pin/80-wire UDMA Cable

  8. The ATA-5 controller brought far faster UDMA modes as well as autodetection of the 80-wire UDMA cable. If the controller does not detect the cable it will force the channel to run at UDMA mode 2 even though the drive and controller can run faster. This is because of the high frequency of higher UDMA modes will cause large numbers of data transfer errors across the wire. UDMA does pack a CRC with the block of data being transfered from the drive to the controller and vice versa so the devices will detect the error incurred across the cable and retry the transfer, but this wil ccur so often that the effective transfer rate at higher modes on the old cables will be slower than just defaulting to UDMA mode 2 where almost no data loss and retries would occur.

  9. The ATA-6 controller brought 100MB/sec transfer rates and formally defined 48-bit LBA. ATA-6 controllers claim that non-LBA mode transfers from controller to drive have been rendered obsolete. If the drive does not understand true 28-bit or 48-bit LBA then the transfers cannot occur. I have observed "Normal" (what many BIOS manufacturers call CHS) as an available option and used it on the ATA-6 controllers in the lab so this appears to be either discretionary on the manufacturer or perhaps they really mean deprecated. ATA-6 controllers introduce a small modification to the IDE language that allows an IDE command request form the controller to the drive for a 16-bit number to hold the number of sectors being requested in a read/write operation. The old language used an 8-bit number for this field which meant that a controller could request to read up to 255 sectors with a single command. Using the 16-bit value allows the controller to ask for up to 65,535 sectors from the drive with a single IDE command. As files swell in size this does make more sense.

  10. The latest ATA-7 controllers boast 133MB/sec transfer rates. These controllers have been formally defined by ANSI yet so will be tentatively referred to as ATA-7? featuring UDMA mode 6?. These will be the last of the ATA controllers because SATA is already being used and the committees are working on this specification now. Until we get official documentation for ATA-7 we cannot be certain of what technologies it includes other than the obvious 133MB/sec tranfer rate. By the way, if you are interested in seeing the formal ATA standards and proposals (ATA-7 is currently a proposal) you will find them here: www.t13.org.

(E)IDE - (Enhanced) Integrated Drive Electronics
  1. Integrated Drive Electronics was spearheaded by all of the major hard drive manufacturers back in the late 80's. The very first hard drive intended for the microcomputer market was the Seagate ST-506 controller and a 5MB 5 ¼" full height (2") hard drive. Later Seagate developed the ST-412 which could handle larger capacity HDD's. This would be the one to debut in the IBM XT.




  2. Their popularity over booting from a 5 ¼" DOS diskette and running applications and saving files on a 5 ¼" Drive B: was enormous. HDD's were going to come down in price go up in capacity and become the main stay of microcomputing. The technology at this point splintered. The next technology was called ESDI - Enhanced Small Device Interface. This was capable of handling larger drives and faster transfer rates and did move some of the intelligence from the controller out to the hard drive itself, but not all of it and the interface still suffered from many drives that would fail to work on other controllers. The final blow for ESDI was when IDE became affordable.

  3. IDE moves all of the HDD controller logic into a circuit board mounted on the drive itself. IDE defined an industry standard language for communicating across the ribbon cable (essentially the IDE bus). And IDE defined a high speed peripheral interface controller to attach to the ISA bus: the ATA controller.

  4. Early work in IDE, in which the HDD's controller would be mounted on the HDD itself and it would not require an external controller card at all, plugged drives directly into the ISA bus. Some of these were interface controller cards with a hard drive built right onto them and were known as hard-cards.


  5. This hard card features a 50MB hard drive attached directly to the ISA controller (it is under the black plastic shell). Now the drive and controller are a single unit that can be moved from one PC to another. One more step toward true IDE.

  6. As the card went down in size and a standard was being developed it was discovered that the HDD would never actually need any more than 40 of the ISA bus lines. These could be brought out to a pin jumper block and a ribbon cable could be attached to this running the ISA bus lines to a hard drive mounted in a forward bay like before. These early XT-IDE's as they came to be called are completely obsolete and incompatible with the modern IDE interface since they do not participate on the IDE bus but expect to be connected directly to the ISA bus.

  7. It was discovered that a poorly designed controller or even a misbehaving hard drive could bring down the entire ISA bus if it was attached directly to it. It was finally decided that a true controller would have to be placed between the HDD's and the ISA bus to manage the enormous communication discrepancies between HDD's and high speed peripherals.

  8. Once the industry gave in to this, the ATA controller grew into a powerful peripheral capable of autodetecting drives and their geometry once an IDE language was developed.

  9. The IDE/ATA-1 specification dealt with the bulk of the low level engineering and programming issues concerning the signaling in the cables, the language the devices would use and so forth. The original specification also established the fact that an ATA controller can control one or two devices on the cable (IDE bus). Their names were made a little more colorful than Drive 0 and Drive 1 (which is exactly what they are) and instead they are called Master and Slave. The original BIOS implementation intended for the Master drive to have the bootable partition on it, hence the name. These days a BIOS could boot from any partition on any drive. The only way to set the drive to participate on the bus as either Master or Slave is with jumpers.


  10. The engineering specification for the IDE ribbon cable aside from the 40-signal wires is that it cannot exceed 18", otherwize data loss could occur. The cable has two (single device cable) or three standard female pin jumper block connectors. The middle connector is not usually in the middle. The remote end connector is intended to connect to the motherboard, but unlike the floppy drive cable which is position sensitive, the IDE cable is not. So it can be turned around, but the middle connector should never be used on the motherboard. If the cable is a "cable select" type of cable then it cannot be turned around. It chooses which drive is Master and which is Slave, but the drives must still be jumpered to accept this assignment from the IDE cable.

  11. The new UDMA cables contain 80-wires, the 40 extras run in between the standard 40 signal wires and are attached to ground. They absorb the rising number of stray electrons that jump out of the wires as the transmission frequencies increase. This is a "cable select" type of cable. In order to use it you must set the jumpers on the devices to their Cable select settings. The blue connector must attach to the motherboard ATA/IDE connector. The gray connector sets the drive to Slave, and the black connector sets the drive to Master. The way it does this is simple. The drive select wire reaches the first (middle) connector so it can bring a "1" to that drive when it is selected, Drive 1 = Slave. The wire does not continue to the opposite end connector and so it can never receive the drive select "1", it always sees a "0" in the drive select line Drive 0 = Master.


    Standard 40-pin/40-wire IDE Cable

  12. The ATA-1 and the original IDE specification suffered some shortcomings which were quickly addressed. Western Digital Corp. led the march to standardize a second ATA controller, retain the original IDE language but expand it offering a "superset" of features including plenty of room for each manufacturer to implement custom or proprietary commands on the bus that only their drives would recognize but which would not confuse or crash older drives. This led to the ATA-2 controller and that generation of HDD's became known as "EIDE" drives meaning Enhanced Integrated Drive Electronics. EIDE was a Western Digital marketing name for their own drives that has become over time a pseudo standard term for ATA-2 and better HDD's.

Serial ATA
  1. These parallel transfer ATA controllers and their associated HDD's are currently considered deprecated technology; still supported but their manufacture is being dropped in favor of the new SATA technology. As SATA becomes more and more popular with the help of industry wide support including incorporation into the latest Intel chipsets parallel ATA and its associated HDD's will be obsolete within a few years.

  2. SATA controllers and hard drives use the IDE language and signals developed throughout the 10 year reign of the parallel ATA controllers generations 1 through 7, but actually physically transmit the signals, command codes and data one bit at a time across a single line in a very high speed serial format similar to the basic conceptual approach used by USB. The electrical signal properties and the encoding can be made extremely robust and at very high speeds there are no problems with latency timing between multiple lines as there would be in parallel communications.

  3. SATA power connectors differ from the legacy Molex style drive power connectors because they provide three +3.3VDC power input lines as well as three +5VDC input feeds. Modern drives are therefore improving in that the internal circuitry and the motors can run on lower voltages and use less wattage leading to less electricity consuption by the PC as well as less heat being produced by the drive. SATA power connectors are keyed so that they cannot be accidentally reversed.

  4. SATA data cable connectors differ significantly from the old standard IDC40 connectors. They are serial so have a far lower pin count, but in addition to this, they have been designed specifically for the SATA specification based technologies and are not standard "off-the-shelf" electronic connectors. This is typical of the PC industry. Technologies start by using standard electronic conponents and connectors and as they become popular the PC industry can design specific role dedicated circuitry chips, as well as their own cables and connectors because they have enough volume sales to afford the research and development and industrial manufacturer retooling costs needed to develop these components.


    Western Digital model WD400JD 40GB SATA-I hard drive w/Legacy Molex Power Connector


    Part of the Western Digital Support Diagram from their website for the above drive.

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    Copyrightę2000-2007 Brian Robinson ALL RIGHTS RESERVED