The Enhanced IDE/Fast-ATA FAQ
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The Enhanced IDE/Fast-ATA FAQ

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General questions

3 General questions

Contents of this section

3.1 What are the main features of EIDE and Fast-ATA?

The fast transfer modes (PIO modes 3 and 4, multiword DMA modes 1 and 2) are the cornerstones of Fast-ATA and EIDE. These are marketing terms contrived by disk drive manufacturers. Enhanced IDE is a Western Digital trademark; Fast-ATA is a term coined by Seagate, and endorsed by Seagate and Quantum.

EIDE consists of:

Fast-ATA and Fast-ATA-2 embrace:

  • PIO mode 3 (and 4 for Fast-ATA-2), multiword DMA mode 1 (and 2 for Fast-ATA-2),
  • Read/Write multiple commands (also known as block mode; see Q 10.6 ),
  • LBA mode.

The difference between the two schemes is mainly in the scope of EIDE. Hardware can be tagged 'EIDE' even if only part of the EIDE feature set has been implemented, which can lead to some confusion. This FAQ will avoid the term EIDE whenever possible, discussing its component parts (ATA-2, ATAPI, etc) instead. This allows you to see exactly what 'EIDE' features you need in your specific situation.

3.2 What are the main features of Ultra-ATA?

To everything EIDE has on offer, Ultra-ATA adds the following:

  • Even faster transfer modes, most importantly DMA/33 with double the bandwidth of DMA mode 2 and PIO mode 4. There are no new PIO modes.
  • Improved reliability using DMA/16 and DMA/33. A checksum is added to the data sent over the ATA interface. That way, data corruption can be detected and the data retransmitted. On an ordinary EIDE interface you wouldn't notice the corruption until it was too late.

Ultra-ATA was first proposed by Quantum and is widely accepted now.

3.3 Are those rumors about buggy interfaces true?

Very true, unfortunately.

This FAQ doesn't really deal with specific interfaces, but two very popular interface chips have been shown to contain bugs too serious to ignore:

In both cases, the corruption occurs only in specific software environments and is very subtle; you can go on working for months without suspecting anything more than buggy software. The damage can be immense. For all the details, look at Roedy Green's ( roedy@bix.com ) "PCI EIDE controller flaws" FAQ included with his EIDE test program which will test your system for the bugs.

BE WARNED that you're playing Russian roulette with your data if you continue working on an affected machine without taking notice of this problem.

3.4 What is a megabyte?

The word "mega" is an ISO prefix designating a factor 1,000,000. A proper megabyte is 1,000,000 bytes. Because computers use binary technology and like working with powers of two, 2ˆ20 bytes, that is 1048576 bytes, is also usually referred to as a megabyte.

Which of the two types of megabyte you're dealing with depends on the context. For storage devices, a megabyte usually means 1,000,000 bytes. Some software uses "binary" megabytes, though, and will show a smaller capacity than the drive label says! This includes most BIOSes.

This FAQ uses megabytes of 1048576 bytes throughout.

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Table of contents of this chapter, General table of contents

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Created by: Astalalista - Last modification: 2004/Jan/26 at 02:57
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