ATA-2, Fast-ATA and EIDE

ATA-2 was designed as an enhancement to the original ATA. This was done because ATA was quickly found to be a limitation as hard drive technology evolved. ATA-2 is EIDE, or Enhanced IDE. ATA-2 includes features such as PIO and DMA modes. These are basically performance enhancing features and are discussed below.

The main benefits of ATA-2 are:

• Increased Capacity. This is basically due to an advancement in BIOS to allow drives larger than 528 MB. This limit was there basically because of the geometry in the drive. Newer enhanced BIOS are capable of using translation modes, thereby using different geometry when talking with the drive than when talking with the software. If your BIOS is dated around 1994 or later, it is probably enhanced. You can tell if it offers settings such as LBA (Logical Block Addressing), a method of translaction which enabled the capacity of drives to exceed 528MB.


• Faster Data Transfer. This is what everyone is after these days. ATA-2 offers several different modes for higher performance. Most drives today are capable of PIO Modes 3 and 4, which are very fast. PIO (Programmed I/O) modes determine the speed at which data is transferred to and from the drive. Below is a table of the PIO Modes:
  
  
  
  
  
  

  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  

  PIO Mode	Transfer Rate	ATA Ver.
  0	3.3 MB/sec	ATA-1
  1	5.2 MB/sec	ATA-1
  2	8.3 MB/sec	ATA-1
  3	11.1 MB/sec	ATA-2
  4	16.6 MB/sec	ATA-2

  
  

  To run Mode 3 or 4, the IDE port must be on a VL-bus or PCI bus connection. Some newer boards with two IDE connectors only have the IDE 1 connected to the PCI bus, while the second IDE connector uses an ISA bus, only capable of Mode 2. One should look into this before buying a new motherboard.



• DMA Transfer. ATA-2 drives support Direct Memory Access transfers, which means that data is transferred directly from the drive to memory, bypassing the CPU. These drives only support the feature. Most OSes do not support it. Proper software support for this transfer is needed before it can be taken full advantage of.

The term EIDE (Enhanced IDE) is a term referring to the Western Digital implementation of ATA-2. The term has come to be the generic term people use to refer to ATA-2. Fast-ATA is another implementation backed by Seagate and Quantum. Speed-wise, there is really no difference between drives said to be ATA-2, Fast-ATA or EIDE.

ATA-3

ATA is a newer implementation of ATA that uses an enhanced PIO mode 4 (used for higher data transfer speeds). ATA-3 also brought in some enhanced power management features, the introduction of SMART technology, as well as some simple password-based security. SMART stands for Self-Monitoring Analysis and Reporting Technology. It monitors the drive for anything that might seem out of the ordinary, documents it, and analyzes the data. If it sees something that indicates a problem, it is capable of notifying the user (or, if applicable, system administrator).

In essence, SMART is merely a set of software tools on the drive itself, constantly running diagnostics. They run diagnostics on the motors, the media, the electronic components, and the mechanical components. Another set of monitoring software is often set up on the controller, to monitor the overall reliability of the drive, taking the data given it by the on drive software and checking it against predefined thresholds. The errors that the system can detect can be predicted by a number of methods. For example, motor and/or bearing failure can be predicted by an increase in the drive spin-up time and the number of retries it takes to succeed in spinning up the drive. Or, if the drive notes that the error correction is being used excessively, it can attribute this to a broken drive head or contamination, and alert before the problem gets worse. Granted, there are some things that cannot be predicted with any accuracy. An example of such would be a total electronics failure. There is no reliable manner in which to predict such a failure without highly specialized and expensive equipment, making it less cost effective. This detection of problems is not limited to only physical aspects of the drive. If it detects that the number of write errors is excessive, it can predict an increase in bad sectors and warn the user that the data should be backed up as soon as possible.

ATA-3 is backward compatible with ATA-2, and since there was no new transfer modes between the two, EIDE is still used to refer to ATA-3 drives.

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