Section 2.2. IDE, EIDE, and ATA

   

2.2 IDE, EIDE, and ATA

IDE devices are the most common storage devices in the PC world, especially for the consumer segment. IDE stands for "Integrated Drive Electronics," ATA for "AT attached," where the AT refers to the historical IBM PC AT. Both refer to the same disk drive standard. The basic idea is to have a disk drive with the disk controller integrated into the disk drive itself ”hence the name Integrated Drive Electronics. The IDE/ATA standard specifies a 16-bit bus.

Just as SCSI has evolved through several standards revisions, so has IDE/ATA. The original standard specified use of programmed input/output (PIO) mode, where the main CPU plays a role in every disk I/O. Later revisions switched to using direct memory access (DMA), where the I/O happens without any assistance from the main CPU.

IDE/ATA cabling supports two disk drives at most, with one drive acting as a master and the other as a slave. At any given time, only one drive may be active. A later standard, called EIDE (Extended IDE), supports four disk drives by having a single EIDE controller that behaves like two IDE controllers. A truly multitasking operating system like Windows NT can take advantage of EIDE by issuing two simultaneous I/Os on the two IDE "channels."

The highlights of the various ATA specifications can be summarized as follows :

  • ATA-1 specified the use of programmed input/output (PIO).

  • ATA-2 was defined as an ANSI standard in 1996. ATA-2 specified the use of faster PIO modes and allowed for the use of direct memory access (DMA). ATA-2 also allowed for Plug and Play possibilities by defining an "identify drive" command that returns details of the drive geometry.

  • ATA-3 was defined in 1997 and can be considered to be a minor upgrade to ATA-2 that improved reliability for faster transfer modes. The biggest feature of ATA-3 was defining SMART (Self-Monitoring, Analysis and Reporting Technology), a standard for monitoring the health of disk drives. SMART can be used with both SCSI and ATA drives.

  • ATA-4/ATAPI introduced support for new devices such as CD-ROM drives and Jazz drives. ATAPI stands for "AT Attachment Packet Interface." Support for Ultra DMA, which can move twice the data per clock cycle that regular DMA moves, was also introduced.

ATA devices are still evolving and are starting to narrow the performance and reliability gap with SCSI devices while attempting to retain a price advantage. Further, with the increasing reliability of hardware overall, and with the advent of software to ensure higher reliability (such as software RAID, described in Chapter 9), ATA may someday play a bigger role in the enterprise. That debate is outside the scope of this book.


   
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Inside Windows Storage
Inside Windows Storage: Server Storage Technologies for Windows 2000, Windows Server 2003 and Beyond
ISBN: 032112698X
EAN: 2147483647
Year: 2003
Pages: 111
Authors: Dilip C. Naik

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