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34-pin floppy and 40-pin ATA male connector (on the host or peripheral device)
80 and 40 wire ATA cables for connecting from host to device

AT Attachment ( ATA for short ) is a standard for parallel data transfer between storage media or drives and the corresponding interface of a computer. The term AT indicates the IBM PC / AT ( Advanced Technology ).

AT Attachment Packet Interface ( ATAPI for short) uses this physical interface and extends the protocol of the data interface so that encapsulated SCSI packets can be transmitted over it. The SCSI commands made possible by this extend the range of application of ATA beyond the originally pure hard disk operation. Devices such as removable disks , optical drives and tape drives canalso be used with ATAPI. The packet interface is still used with Serial ATA .

The functionality made available by ATA is usually taken over in modern computers by the successor development Serial ATA . Since the establishment of Serial ATA, PATA or P-ATA has often been used as an abbreviation instead of ATA because of the parallel data transmission . The term Integrated Drive Electronics ( IDE for short ) comes from the time before standardization and is usually used synonymously with ATA or PATA. The term AT bus was also widespread, but in connection with plug-in cards it also stood for the ISA bus.


The American hard drive manufacturer Western Digital was commissioned by Compaq in 1984 to develop a hard drive controller. In contrast to the ATA predecessors with the ST506 interface (with the MFM or RLL recording method ) and the Enhanced Small Disk Interface (ESDI), communication should take place via a single 40-pin flat cable and a larger part of the controller electronics should be on the Peripheral device (e.g. hard disk ).

Western Digital named this interface Integrated Drive Electronics (IDE) (1986). In cooperation with other hard disk manufacturers, this was established as a common standard, which was adopted in 1989 as ATA-1. To this day, the term “IDE” is a synonym for “ATA” or today “ PATA ”.

Western Digital expanded and improved this standard with new features. The marketing name EIDE for "Enhanced IDE" (corresponds to ATA-2) was created and has since been used as a generic term for all improvements to IDE. In fact, there are a number of advanced specifications (see below).

Cable select through unequipped insulation displacement connector
Cable select through interrupted line in the flat cable

With the ATA interface, the connected devices have their own controller. With this built-in controller, they communicate with the host via a host adapter on the motherboard or an interface card . ATA devices are connected to the 40-pin interface of the host with a ribbon cable (ATA-40). Two devices per connection are possible, these are referred to as device 0 (also master, MA ) or device 1 (also slave, SL ). Device 0 is usually connected at the end of the cable. The device 0 or -1 status is usually set using jumpers . Many devices also have the option of “Cable Select” (CS). To do this, both devices must be set to CS, whereby a special connection cable assigns the device 0 or -1 status.

The original ATA instruction set was intended exclusively for hard drives. In order to be able to use removable media, optical and tape drives, a procedure was defined with ATAPI to transmit (a subset of) SCSI commands in packets via the ATA interface. ATAPI is based on ATA and extends the functionality. Since both protocols have been described in a common standard since ATA / ATAPI-4, the term ATA / ATAPI is commonly used.

About the nomenclature

The abbreviation “AT” in “AT Attachment” refers quite obviously to IBM's “ Advanced Technology ”, but officially only stands on its own in order to avoid legal problems with IBM.

As indicated in the history section , the transition from the industry standard to an official standard only took place after ATA devices had been manufactured for a long time: The last draft of the standardization body T13 Technical Committee for the ATA-1 standard is dated 1994, although ATA- Devices have been manufactured since the mid-1980s. Therefore, at the time of the publication of the official standard, master and slave had established themselves as the common designation of the two devices that can be addressed by an ATA connection. From a technical point of view, however, these designations do not appear justified, since the control of both devices by the host (usually the computer) is practically equivalent. The publications of the T13 Technical Committee use the terms Device 0 and Device 1 instead , which rather take the technical conditions into account. In its current state, this article uses the T13 Technical Committee nomenclature to reflect the official language that it implies, followed by master and slave in parentheses for general understanding.

Special shape

An adapter for connecting 2.5 ″ notebook disks to common mainboards. The power supply is routed through the cable; the signal lines are located in the black connector housing.
A CompactFlash IDE adapter

ATA 44 : There are special forms of the interface for notebooks that also transmit the supply voltage (+5 V) and, in the case of optical drives, audio signals . These are called ATA-44s for 2.5 ″ hard drives and ATA-50s for slimline optical drives. (The number indicates the number of plug contacts.)

ATA ZIF : For 1.8 ″ hard disks used in media players, there is a special form with a 40-pin socket. However, it is also used in UMPCs and some notebooks.

Versions of the ATA standard

If two devices with different ATA versions are connected to the same cable, with older host adapters the slower device decides on the speed of both devices. Modern ATA host adapters (since around 1998) can control the speed for each device separately, so that slow devices no longer slow down the entire bus.

ATA-1 (1989-1999, ANSI X3.221-1994)

Simultaneous control of a maximum of two hard disks with up to 8.3 MB / s ( MB = megabytes; 1 MB / s = 1000 kB / s = 1,000,000 bytes / s).

ATA-1 works asynchronously.

Several PIO modes ( Programmed I / O ) and DMA ( Direct Memory Access ) variants are used:

  • PIO mode 0: 3.3 MB / s; PIO 1: 5.2 MB / s; PIO 2: 8.3 MB / s
  • Single word DMA mode 0: 2.1 MB / s, DMA single 1: 4.2 MB / s, DMA single 2: 8.3 MB / s
  • Multi Word DMA mode 0: 4.2 MB / s

ATA-2 (1994-2001, ANSI X3.279-1996)

The control and data signals can be transmitted synchronously with the ATA-2. Performance up to 16.6 MB / s. New transfer modes: Block transfers, Logical Block Addressing .

  • PIO mode 3: 11.1 MB / s; PIO 4: 16.6 MB / s
  • DMA mode 1: 13.3 MB / s, mode 2 (DMA 2): 16.6 MB / s (from here always multi word)
  • Fast ATA includes ATA-2, PIO 3, DMA 1
  • Fast ATA-2 includes ATA-2, PIO 4, DMA 2

ATA-3 (1996-2002, ANSI X3.298-1997)

ATA-3 has two new functions compared to its predecessor ATA-2: SMART and the Security Feature Set . Performance and transmission modes have not changed compared to ATA-2.

ATA / ATAPI-4 (1997-2008, ANSI NCITS 317-1998)

With ATA / ATAPI-4, CD-ROM drives and CD burners are integrated into the standard for the first time. For this purpose, the standard is called ATA / ATAPI for the first time, which stands for ATA Packet Interface . The packet interface defines a layer in order to be able to send SCSI commands via the ATA protocol. Performance: 33.3 MB / s. A new mode called Ultra-DMA (UDMA) is introduced. However, ATA / ATAPI-4 is compatible with the old PIO and DMA modes .

  • With UDMA, the standard has been expanded to include the cyclic redundancy check .
  • Ultra DMA mode 0: 16.7 MB / s; UDMA 1: 25.0 MB / s: UDMA 2: 33.3 MB / s.
  • Ultra ATA / 33 is a common abbreviation of ATA-4 with UDMA 2.

The Host Protected Area (HPA) feature can be used to create a protected area on the disk.

ATA / ATAPI-5 (since 1999, ANSI NCITS 340-2000)

ATA-5 contains a new mode: Ultra DMA 4. Performance 66.6 MB / s, hence also called UDMA-66 (UDMA 3: 44.4 MB / s). A special 80-wire cable is required for the ATA-5 standard. It still only has 39 connection pins, but there are 41 additional lines with ground connections between the data lines. These ensure a defined wave impedance of the signal lines to reduce reflections . They also reduce crosstalk between the signal lines. Otherwise, both could lead to transmission errors.

ATA / ATAPI-6 (since 2000, ANSI NCITS 361-2002)

With ATA-6 and the Ultra-DMA-100 (UDMA 5) mode, data rates of up to 100 MB / s are possible. This is why the name ATA / 100 is often found here. New ATA commands have also been introduced that allow 48-bit sector addresses ( LBA -48), which means the maximum addressable capacity of 2 28 512 bytes = 128 GiB to 2 48 512 bytes = 134,217,728 GiB (≈ 144,115,188 GB) = 128 PiB increased.

Another innovation is Automatic Acoustic Management (AAM).

With the Device Configuration Overlay (DCO) it is possible to influence certain values ​​reported in the identify information of a disk. For example, the feature bits for individual DMA modes, SMART features, AAM or HPA can be deactivated or the reported size of the disk can be reduced. With the help of the hdparm system program originally developed for UNIX systems, this information can be queried for a specific hard drive with sudo hdparm --dco-identify / dev / <device name>, for example.

ATA / ATAPI-7 (since 2001, ANSI INCITS 397-2005)

With ATA / ATAPI-7, the standard differentiates for the first time between parallel and serial transmission and the common command set (ATA / ATAPI Command Set, ACS). Retronym the previous standard PATA (parallel ATA) was called and the serial version SATA .

With the PATA mode Ultra-DMA-133 (UDMA 6), data rates of up to 133 MB / s are possible. Therefore the designation ATA / 133 is often found here.

ATA-8 (since 2005, ANSI INCITS 452-2008)

With ATA-8 bugs were fixed and the standard restructured. It is still compatible with the previous versions. What is new, for example, is that ATA-8 is divided into four documents, the Architecture Model (ATA8-AAM), the Command Set (ATA8-ACS), the Parallel Transport (ATA8-APT) and finally the Serial Transport (ATA8-AST) . This allows a further abstraction of the definition of the commands, the architecture model and finally the transport. The ATA8-ACS command set was published in September 2008 as the ANSI INCITS standard.

Was deleted u. a. a chapter on the definition of the hard disk / controller registers, from the official side it was announced: "ATA8-ACS is documenting the command set and not the transport". Another interesting observation is that the software protocol with the hardware implementation has now really been abstracted. If in ATA / ATAPI-7 Volume 1 (corresponds to Command Set and Architecture Model) it was pointed out several times that the SATA interface has a partially different programming / transmission than the PATA interface (see IDE), such information appears in ATA -8 no longer appears, rather many passages have been removed and moved to ATA8-APT and ATA8-AST. The aim is to take a step into the future, because in system programming up to now only the PATA drives have dominated, while there has been great confusion about SATA.

For the first time, there is a standardized option via the SCT Commands to read out the current temperature, minimum and maximum values ​​and the temperature profile of the last operating hours. Hard drives with this function have been available since 2006. The current temperature could previously mostly be determined as a SMART attribute, but that was not part of the ATA standard.

ACS-2 (since 2008, ANSI INCITS 482-2012), ACS-3 (since 2011), ACS-4 (since 2014)

After the publication of the ATA8-ACS standard, the command set was further developed under the names ACS-2, ACS-3 and ACS-4.

A new feature of ACS-2 is "Device Statistics". This enables values ​​such as operating hours, number of resets, number of read and write processes, number of errors and temperature to be queried. In contrast to the SMART attributes, the meaning of all values ​​is standardized.


All new versions are downward compatible up to ATA / ATAPI-4: newer hard disks can also be operated on older computers, older drives can also be connected to newer interfaces.

Max. Data rate: 8.3 MB / s 16.6 MB / s 16.6 MB / s 33.3 MB / s 66.6 MB / s 100 MB / s 133 MB / s
Summary of the ATA / ATAPI versions by year of introduction
1997 Parallel ATA ATA / ATAPI-4 Ultra ATA / 33 Ultra DMA 2 40-core cable 33.3 MB / s CD-ROM
1999 Parallel ATA ATA / ATAPI-5 Ultra ATA / 66 Ultra DMA 4 80-core cable 66.6 MB / s Hard drives, CD-ROM
2000 Parallel ATA ATA / ATAPI-6 Ultra ATA / 100 Ultra DMA 5 80-core cable 100 MB / s Hard drives
2001 Parallel ATA ATA / ATAPI-7 Ultra ATA / 133 Ultra DMA 6 80-core cable 133 MB / s Hard drives

Addressing problems

Older ATA controllers or older system software can often only address hard drives up to a certain capacity. This means that only part of the hard disk capacity can be used. Typical limits are 504  MiB , 8  GiB , 32 GiB, 128 GiB. The 128 GiB limit results from the use of 28-bit LBA , because 28 bits cannot address more than 2 28 sectors (this corresponds to 128 GiB). There is an extension to 48-bit LBA for this, which considerably expands the address space. The other limits are justified by the CHS addressing , i.e. by the division into cylinder, head and sector - where there are separate limits for each individual value, and CHS addressing was already obsolete with the first X3T10 standard. Even today, many system programs - such as boot managers or partitioning tools that load on startup - use CHS addressing.

Modern hardware and software can help. In the past, BIOS updates were often released to fix these problems. With today's standards and software implementations, addressing problems have practically become a problem of the past.

Due to the partition table of the MBR , the use of classic drives in systems is restricted to a 2- TiB limit, which can only be "circumvented" by using the EFI- GUID partition table . The 2-TiB limit is caused by the 32-bit size of the sector information in the partition entries.

An easier way to get around the 2-TiB limit is to increase the size of the data blocks to 1024 bytes or 2048 bytes, which increases the addressable area to 4 TiB or 8 TiB. However, this also increases the smallest possible cluster size to 1024 or 2048 bytes, which is of little relevance because cluster sizes below 4096 bytes are hardly used anyway.

password protection

Most of the ATA and Serial ATA hard drives currently available on the market have a 32-byte password protection with a master and user key, without which the data on the hard drive cannot be accessed. A program running with system rights can set a password and make the data inaccessible to the user.

The security feature set was first used outside of notebooks by IBM in 1998 and has been widely used since Seagate supplied 3.5 ″ hard drives for the Xbox .

The hard disks also allow you to prevent a new password from being set. However, this function must be called every time the system is started. In the BIOS that can happen before the start of the operating system, which is only supported by a few BIOS. An additional tool can be called during the boot process, which locks the hard disk.

Pin assignment

The ATA connector (ATA-40) is a 40-pin, two-row pin header , pitch 2.54 mm (100MIL):

Tub connector on drive (top view of pins)

  39________––________1 ungerade Pin-Nummern
  |·········· ·········|
  40‾‾‾‾‾‾‾‾20(Key)‾‾‾2 gerade Pin-Nummern

Socket strip on the cable (top view, from the front)

   1________––________39 ungerade Pin-Nummern
   2‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾40 gerade Pin-Nummern

With a correctly wired flat cable, pin 1 is on the color (mostly red) marked wire. As an additional security measure, the socket for pin 20 (marked with * in the picture) is closed on many plugs to prevent incorrect connection. When plug with center groove are now not only in the drives themselves but also on controllers and motherboards standard. Since the socket strip has a nose at the corresponding point, polarity reversal is excluded.

The description of the PINs follows:

Pin code ATA signal meaning
1 RESET Resets all drives on this port
2, 19, 22, 24, 26, 30, 40 GND Dimensions
3-5-7- 9-11-13-15-17 DD7..DD0 Data bus, bits 7..0, low byte for 16-bit data transmission
18-16-14-12-10-8-6-4 DD15..DD8 Data bus, bits 15..8, high byte for 16-bit data transmission
20th KEYPIN Pin is missing so that the connector cannot be inserted the wrong way round. However, deviating from the standard, it is sometimes also used for power supply (e.g. for disk-on-module flash memory)
21, 29 DMARQ, DMACK DMA request and acknowledgment, DMA control signals (optional)
23 DIOW Signal to write data
25th DIOR Signal to read data
27 IORDY I / O ready, low level: Requires additional clock cycles for the current I / O cycle (often not used)
28 CABLE SELECT, on very old hard drives SPINDLE SYNC Allocation of the drive as DRIVE0 = low or DRIVE1 = high, on very old hard disks spindle synchronization between device 0 and 1 (at that time master and slave ), e.g. B. for drive arrays (often not implemented)
31 INTRQ Interrupt request
32 IOCS16 Selection of 16-bit transfer
34, 39 PDIAG , DASP Passed diagnostics from device 1, drive active / device 1 present, feedback from device 1 to device 0 during initialization
36-33-35 DA2..DA0 Address bus bits 2..0, addressing of the internal registers within the command or control register set of the drive
37, 38 CS1Fx , CS3Fx (also CS0 , CS1 ) Chip selection signals from the host to select the Command Register or Control Register register sets. With the PC architecture, these are normally in the I / O address space from 1F0h or from 3F0h.

With the ATA-44, which is mostly used with 2.5 ″ hard drives, the pin spacing is reduced to 2.00 mm. The assignment corresponds to ATA-40, but here the power supply is provided via additional pins on the ATA connector.

Pin code ATA signal meaning
41 +5 V (logic) Power supply for electronics
42 +5 V (motor) Power supply for motor
43 GND Dimensions

ATA cables: colors of the plugs

On the newer 80-core ATA-5 cables, the plugs have three colors:

Blau: Controller/PC
Grau: Slave (Device 1 / IDE 1)
-- 79 Adern: Master/Slave-Signalleitung 28 gekappt/unterbrochen
Schwarz: Master (Device 0 / IDE 0)

This is important for:

  • Fast UDMA modes : From UDMA-66 (UDMA 4) onwards, the finer, 80-core flat ribbon cable is used, in which every second core is connected to ground, which shields the signal cores from one another and makes the higher speed possible. As usual, the plugs have 40 pins , but the connector on the host adapter side has a special coding ( PDIAG is separated and a capacitor with a certain value is connected to ground on the host adapter), by which the ATA host adapter can recognize that such a cable is being used . Only then does the host adapter enable the faster modes of 66 MB / s and higher. When connecting the ATA devices with such a cable, it should therefore be noted that the blue end of the cable must be connected to the motherboard or the ATA host adapter.
  • Cable-Select : ATA cables have been supporting cable-select addressing for a long time and have device plugs in gray and black to which the ATA devices are connected. If addressing is carried out using the cable select method, the device on the black connector is automatically Device 0 (master) and the device on the gray connector is Device 1 (slave). The signal line 28 is only connected to the master, but not to the slave. To use this method, both must ATA devices to "CS" gejumpert be. Otherwise one device has to be jumpered to "Master" and the other to "Slave"; with manual jumpering it does not matter which is connected to the black and which to the gray connector. If only a single ATA device is connected to the cable, the plug in the middle of the cable must be left free, as an unused cable end e.g. B. can cause interference in the form of signal reflections .

See also

Notes and sources

  1. Serial ATA Work Group: Serial ATA: High Speed ​​Serialized AT Attachment , Revision 1.0a, Jan 7, 2003
  2. a b c Due to the missing key pin, the interface only has 39 poles.
  3. Working Draft - X3T10, 791D, Revision 4c - AT Attachment Interface for Disk Drives ( Memento from June 17, 2016 in the Internet Archive ) (ATA 1)
  4. The corresponding counterpart, a closed hole in the cable socket, was only generally accepted with 80-core cables. Most 40-core cables can, however, be plugged the wrong way round onto the 39-pin connector despite the keypin.

Web links

Commons : AT Attachment  - album with pictures, videos and audio files