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Serialized, overlapped, and queued operations

July 9, 2011

The parallel ATA protocols up through ATA-3 require that once a command has been given on an ATA interface, it must complete before any subsequent command may be given. Operations on the devices must be serialized—with only one operation in progress at a time—with respect to the ATA host interface. A useful mental model is that the host ATA interface is busy with the first request for its entire duration, and therefore can not be told about another request until the first one is complete. The function of serializing requests to the interface is usually performed by a device driver in the host operating system.

Lowest speed

July 9, 2011

It is a common misconception that, if two devices of different speed capabilities are on the same cable, both devices' data transfers will be constrained to the speed of the slower device.

Current terminology

July 7, 2011

The terms "integrated drive electronics" (IDE), "enhanced IDE" and "EIDE" have come to be used interchangeably with ATA (now Parallel ATA, or PATA).

x86 BIOS size limitations

July 7, 2011

Initially the size of an ATA drive, then called "IDE" was stored in the system x86 BIOS using a a type number 1 - 45 that predefined the C/H/S parameters.[14] and often the landing zone as well. Which decides where to park the drive heads. Later a "user definable" format[14] called C/H/S or cylinders, heads, sectors were made available. These numbers were important for the earlier ST-506 interface, but were generally meaningless for ATA -- the CHS parameters for later ATA large drives often specified impossibly high numbers of heads or sectors that did not actually define the internal physical layout of the drive at all. From the start and up to ATA-2 every user had to specify explicitly how large every attached drive was. From ATA-2 an "identify drive" command were implemented that can be sent and which will return all drive parameters.

Interface size limitations

July 7, 2011

Due to lack of foresight the first drive interface used 22-bit addressing mode which resulted in a maximum drive capacity of 2 GByte. Later the first formalized ATA specification used a 28-bit addressing mode, allowing for the addressing of 228 268 435 456 sectors (blocks) of 512 bytes each, resulting in a maximum capacity of 128 GiB (137 GB).

Parallel ATA interface

July 7, 2011

Parallel ATA cables transfer data 16 bits at a time. The traditional cable uses 40-pin connectors attached to a ribbon cable. Each cable has two or three connectors, one of which plugs into an adapter interfacing with the rest of the computer system. The remaining connector(s) plug into drives.

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