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Advanced Technology Attachment

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Advanced Technology Attachment (ATA), is a standard interface for connecting storage devices such as hard disk drives and CD-ROM drives inside personal computers. It is referred to in many ways, including abbreviations such as IDE, ATAPI, and UDMA. ATA standards only allow cable lengths in the range of 18 to 36 inches, so it is normally used as an internal computer storage interface. It is the most common and the least expensive interface for this application.

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History

Although ATA was the only proper name for the standard all along, for marketing reasons, an early version of the standard was called Integrated Drive Electronics (IDE), and the one following it Enhanced IDE (EIDE). With the introduction of Serial ATA around 2003, this configuration has been retroactively renamed Parallel ATA (P-ATA), referring to the method in which data is transferred over wires in this interface.

The interface only worked with hard disks at first. Eventually, the standard was extended to work with a variety of other devices, which generally use removable media. Mainly, these devices are CD-ROM drives, tape drives, and large-capacity floppy drives such as the Zip drive[?] and SuperDisk drive[?]. The extension is called the Advanced Technology Attachment Packet Interface (ATAPI), with the full standard now known as ATA/ATAPI

Another important transition in the history of ATA is the movement from programmed input/output (PIO) to direct memory access (DMA). These are methods for accessing and transferring data within computers. PIO was an inefficient method, and required a significant amount of oversight by the computer's central processing unit. This meant that systems based around ATA devices were generally much slower at disk-related activities than computers using SCSI or other interfaces. However, DMA (and later Ultra DMA or UDMA) greatly reduced the amount of processing time the CPU had to use in order to read and write the disks.

ATA devices have suffered from a number of "barriers" in terms of how large they can be (in terms of data capacity). However, most of these barriers have been broken with new addressing systems and programming techniques. Some of the ATA-specific barriers include: 504 megabytes, 32 gigabytes, and 137 gigabytes. A variety of other barriers have existed, but those were usually due to poorly written drivers and disk input/output layers in operating systems. Even the barriers listed above mostly came about due to poorly written BIOSes.

Parallel ATA Interface

Up until the introduction of Serial ATA, 40-pin connectors were used to attach drives to a ribbon cable. Each cable has two or three connectors, one of which is attached to a controller that interfaces with the rest of the computer system. The remaining one or two connectors are attached to drives. Parallel ATA cables transfer data 16 bits at a time.

For most of ATA's history, ribbon cables had 40 wires, but an 80-wire version was introduced when the Ultra DMA/66 standard came out. The 80-wire cable provided a better signal and enabled the 66 megabyte per second transfer speed of that standard.

With the release of successive high-speed versions of the ATA standard in the late 1990s, the original cable length specifications became much less generous. With maximum length now just 18 inches, it can be difficult to connect drives when large computer cases are used, or when several drives are in one computer.

If two drives are attached to a single cable, they are generally configured to have one drive as master and the other as slave. This merely means that the master drive shows up ahead of the slave drive in the computer's operating system.

If only one drive was connected, it is usually configured as master. However, some drives have a special setting called single for this mode of operation. Also, depending on the hardware and software available, a single drive can operate as the slave drive.

A drive setting called cable select has also emerged. In this mode of operation, the computer attempts to automatically manage the master/slave configuration. However, this can be problematic if the computer's operating system doesn't understand how to manage this situation.

Serial ATA

The largest change in ATA happened with the introduction of Serial ATA (see article for more details). This interface uses 7-pin cables for the data connection, and the data is transmitted serially rather than in parallel. In addition, Serial ATA should give users the ability to hot swap[?] hard drives. This adds a capability that more expensive systems such as SCSI and Fibre Channel have had for a long time, though it remains to be seen how widely that aspect of the technology will be used.

The transition to Serial ATA should largely be transparent to the operating system, though new features will probably need to be added to make full use of the technology.

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