Terms Used in Describing ATA/UDMA Devices

ATA/UDMA Device Definitions

Hard drive technologies are expanding at a meteoric rate, like so many other computer technologies today. Just a short time ago, there were two terms to define hard drives, IDE and SCSI. Today, as new drive technologies develop and old ones expand, the terms that define them are added to an ever-growing list of definitions to remember.

Many times more than one term or definition is used to describe the same device type, and some terms have nothing more than the addition of a prefix or suffix to differentiate between technologies. In an effort to reduce some of the inherent confusion, we developed the following information to help you understand the differences between ATA, ATA-2, ATA-3, PIO, DMA, UDMA, etcetera.

ATA (AT Attachment — AT refers to the IBM Personal Computer AT)

AT Attachment refers to a set of device interface standards or specifications that are used in the design of storage devices for most personal computers. This is often confused with the marketing terms “IDE” and “EIDE”, which describe devices that conform to the ATA specification.

ATAPI (AT Attachment Packet Interface) is that part of the interface standard used to define removable media storage devices such as CD-ROM, DVD, Tape, ZIP, and JAZZ drives.

ATA (aka ATA-1 or IDE) — ANSI document number.

ATA is the actual standard for what is commonly referred to as IDE. The ATA standard defines Programmed Input Output (PIO) modes 0, 1, and 2, and Direct Memory Access (DMA) mode 0. In 1999, at the recommendation of NCITS T13, ATA (ATA-1) was withdrawn as an ANSI standard.

ATA-2 (aka EIDE, FASTATA or FAST ATA) — ANSI document number X3.279-1996.

ATA-2 is the actual standard for what is known today as EIDE. ATA-2 introduces the higher speed data transfer modes of PIO Modes 3 and 4, in addition to Multiword DMA Modes 1 and 2. These modes allow the ATA interface to run at data transfer rates up to 16.6 MB/sec.

ATA-3 — ANSI document number X3.298-1997.

While the ATA-3 specification has introduced some new features, such as S.M.A.R.T. and Security, it does not introduce any new PIO or DMA data transfer modes. Contrary to the beliefs of some, there is no such thing as PIO mode 5.

ATA/ATAPI-4 — ANSI document number NCITS.317-1998.

ATA/ATAPI-4 specification adds and changes many things. Here is a brief list:

  • It added new ATAPI command and reset protocols.
  • It changed or modified many old ATA commands and features, such as the Format Track and Read/Write Long commands, making them obsolete.
  • It added a data transfer protocol named Ultra DMA, added data integrity checking (via a CRC check) and created much higher data transfer rates (up to 33MB/second).
  • It added a command overlapping and command queuing protocol for both ATA and ATAPI devices.
  • It added many new, but minor, features for both ATA and ATAPI devices.


ATA/ATAPI-5 completed its final editing process at T13 and was published as an ANSI standard in the year 2000. ATA/ATAPI-5 deletes a few old commands, adds a few new commands, and changes the way a few commands operate. The single biggest change the occurred as the result of ATA/ATAPI-5 are the two new and faster Ultra DMA 66 data transfer modes.


In late 1999, ATA/ATAPI-6 became next logical, (and official) T13 project. The proposals that did not make it into ATA/ATAPI-5 were added in ATA/ATAPI-6 specifications. Those proposals included increasing the size of the LBA from 28 bits to 64 bits, increasing the Sector Count (transfer size in sectors) from 8 bits to 16 bits, increasing the Ultra DMA timing mode (to ATA/100), and adding new commands for Audio/Visual (AV) applications. ATA/ATAPI-6 arrived in the marketplace in early in 2000.

Original Standard
Max Bus Speed
PIO Mode 0
3.33 MB/sec
DMA Mode 0 or Multiword DMA Mode 0
4.16 MB/sec
PIO Mode 1
5.22 MB/sec
PIO Mode 2
8.33 MB/sec
PIO Mode 3
11.1 MB/sec
DMA Mode 1 or Multiword DMA Mode 1
13.3 MB/sec
PIO Mode 4
16.6 MB/sec
DMA Mode 2 or Multiword DMA Mode 2
16.6 MB/sec
Ultra DMA Mode 0
16.6 MB/sec
Ultra DMA Mode 1
25.0 MB/sec
Ultra DMA Mode 2, UDMA33 or ATA/33
33.3 MB/sec
Ultra DMA Mode 3
44.4 MB/sec
Ultra DMA Mode 4, UDMA66 or ATA/66
66.6 MB/sec
Ultra DMA Mode 5, UDMA100 or ATA/100
100 MB/sec

* ATA/ATAPI-5 was not an officially approved standard as of 11/1/2000.
** ATA/ATAPI-6 wa not an officially approved standard as of 11/1/2000.

In PIO Mode, the systems microprocessor gets involved in transferring the data back and forth between the storage device and system memory through the input or output ports.

In DMA Mode, the task of transferring data is handled via a bus-mastering system controller called the DMA controller. The DMA controller is set up or programmed to handle the DMA transfer. This relieves the processor from the duty of handling data transfers, thereby allowing it do other tasks.

The maximum ATA cable length is 18 inches for both the 40- and 80-conductor cables.

The minimum ATA cable length is 10 inches for the 80-conductor cable. The 40-conductor cable has no minimum length specified.

The 40-conductor ATA cable is specified for use on devices that use up to and including Ultra DMA mode 2 or ATA/33 data transfer mode.

The 80-conductor ATA cable is optional for use on devices that use Ultra DMA mode 2 or ATA/33, but required for use on devices that use Ultra DMA mode 3 and higher, as defined in the ATA/ATAPI-5 specification.

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