IDE Hard Drive Technical Information

  Integrated Drive Electronics (IDE) refers to any drive with the controller built-in (integrated) into the disk. Although it really refers to a general technology, most people use the term to refer the ATA specification, or Advanced Technology Attachment.

    There are several versions of ATA (IDE), all developed by the Small Form Factor (SFF) Committee:

• ATA : Known also as IDE, supports one or two hard drives, a 16-bit interface and PIO (Programmed Input/Ouput) modes 0, 1, and 2.
  
• ATA-2 : Supports faster PIO modes (3 and 4) and multi-word DMA (Direct Memory Access) modes 1 and 2. It also supports LBA (Logical Block Addressing) and block transfers. ATA-2 is marketed as Fast ATA or Enhanced IDE (EIDE) .
  
• Ultra-ATA : Also call Ultra-DMA, ATA-33, and DMA-33 , supports multiword DMA mode 3 running @ 33 MBps.
  
• ATA/66 : A version of ATA proposed by Quantum Corporation and supported by Intel that doubles ATA's throughput to 66MBps.
  
• ATA/100: An updated version of ATA/66 that increases data transfer rates to 100 MBps.

 

The Origin of the IDE/ATA Interface

     CDC, Compaq, and Western Digital were the first to create the IDE/ATA hard drive interface. They also decided to use the 40-pin connector. The original hard drives were large drives of the 5.25" form factor, but were only 40 megabyte. They were used in the early Compaq 386 systems, using Western Digital controllers. Later, Compaq founded Conner hard drives. Conner produced drives for Compaq, but was later sold. In the late 1980's, the ATA IDE was set as ANSI standard. This caused all manufacturers to agree with a common design for the interface. But, before this was done, many companies had produced their own variations. This sometimes makes it hard for computer troubleshooters to make these older drives work with newer ones in the same system. Some areas of the ATA standard were left open to manufacturer's for their own commands. Due to this, the standard is really loosely set. Low-level formatting drives require a program tailored to hard drives from a certain manufacturer, one that knows that company's commands.

Dual IDE Hard Drives

   Using two drives in the same system with the original specification was known to be hard at times. This is usually due to each hard drive having its own controller, and both trying to operate over the same bus. One of the nice features introduced with ATA specification was the ability to operate two drives together in a chain. The primary drive is the master, and the second drive is the slave. On most drives, you tell it to be a master or a slave with jumper settings on the drive itself. When two drives are on the same ribbon cable, all commands are received by both controllers. Each drive must respond only to commands meant for it.