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Overview: Performance Of PIO Modes

IDE Training Course, Part 1: A Detailed Look at the Basics and Technology
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PIO Overview Cycle time Data transfer Implemented
PIO mode 0 600 ns 3.3 MB/s Since ATA-1
PIO mode 1 383 ns 5.2 MB/s Since ATA-1
PIO mode 2 240 ns 8.3 MB/s Since ATA-1
PIO mode 3 180 ns 11.1 MB/s Since ATA-2
PIO mode 4 120 ns 16.6 MB/s Since ATA-2
Overview: Performance Of DMA Modes
DMA Overview Cycle time Data transfer Implemented
Single Word DMA 0 960 ns 2.1 MB/s Since ATA-1
Multi Word DMA 0 480 ns 4.2 MB/s Since ATA-1
Single Word DMA 1 480 ns 4.2 MB/s Since ATA-1
Multi Word DMA 1 150 ns 13.3 MB/s Since ATA-2
Single Word DMA 2 240 ns 8.3 MB/s Since ATA-1
Multi Word DMA 2 120 ns 16.6 MB/s Since ATA-2
Overview: Performance Of UltraDMA Modes
UltraDMA overview Cycle time Data transfer Implemented
UltraDMA 0 240 ns 16.6 MB/s Since ATA-4
UltraDMA 1 160 ns 25 MB/s Since ATA-4
UltraDMA 2 120 ns 33.3 MB/s Since ATA-4
UltraDMA 3 90 ns 44.4 MB/s Since ATA-5
UltraDMA 4 60 ns 66.6 MB/s Since ATA-5
UltraDMA 5 40 ns 100 MB/s Since ATA-6
UltraDMA 6* 30 ns 133 MB/s With ATA-7*
* subject to change. This standard may never be adopted officially as the successor technology, Serial ATA, is ready for takeoff.

ATAPI: CD-ROM Drives Get Connected

ATA was never intended initially to communicate with drives other than hard drives. The first CD-ROM drives used SCSI, or they were connected to the system using their own interface card - not a very advanced method, considering the fact that it basically duplicated the ATA system. By the way, the progression to ATAPI also brought higher performance to tape drives, as until then those had only been connected via the slow-paced floppy controller.

Data is sent in packets, hence the name "Packet Interface." As a matter of fact, the ATAPI protocol no longer has anything in common with ATA; instead, it is akin to the working principle of SCSI. Unlike with hard drives, the protocol used can differ greatly from model to model, whereas in the case of today's hard drives the protocol conforms to either UltraDMA/100 or UltraDMA/133. In addition, ATAPI absolutely needs a driver to communicate with the drive, while most of the time BIOS is able to access hard drive data directly. Booting from the CD-ROM drive has not been a problem for a while now. Yet added features, such as playing audio CDs without having to load an operating system, have been mastered by only a few motherboard manufacturers (e.g., AOpen).

For the Sake of Form: Standardization Committees

The following represents a hierarchical listing of all the organizations involved in the standardization process:

  • American National Standards Institute: ANSI
  • ANSI handles the development and the adoption of standards of all kinds. In doing so, however, it does not have an active role, but merely takes care of the "management" side: it appoints other organizations as Standards Developing Organizations (SDOs), which are the ones doing the actual work. Once the work is done, ANSI ultimately handles the promulgation of adopted standards.

  • Information Technology Industry Council: ITIC ITIC is a group comprised of several dozens of companies. It's the branch in charge of the development of all the standards in computer technology, hence an SDO.
  • National Committee for Information Technology Standards: NCITS is a commission of the ITIC, handling the support and further development of standards within the computer industry. It used to be called X3. NCITS is deeply structured so that there are various subunits for all of the relevant areas.
  • T13 Technical Committee: T13 is the unit responsible for the development of ATA today.
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