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[ The PC Guide | Systems and Components Reference Guide | Hard Disk Drives | Hard Disk Interfaces and Configuration | Integrated Drive Electronics / AT Attachment (IDE/ATA) Interface | IDE/ATA Transfer Modes and Protocols ]

16-Bit and 32-Bit Access

One of the options on some chipsets and BIOSes is so-called 32-bit access or 32-bit transfers. In fact, the IDE/ATA interface always does transfers 16 bits at a time, reflecting its name ("AT attachment"--the original AT used a 16-bit data bus and a 16-bit ISA I/O bus). For this reason, the name "32-bit" access or transfer is somewhat of a misnomer.

Since modern PCs use 32-bit I/O buses such as the PCI bus, doing 16-bit transfers is a waste of half of the potential bandwidth of the bus. Enabling 32-bit access in the BIOS (if available) causes the PCI hard disk interface controller to bundle together two 16-bit chunks of data from the drive into a 32-bit group, which is then transmitted to the processor or memory. This results in a small performance increase.

Note: Some BIOSes (or add-in controller cards) may automatically and permanently enable this feature, and therefore not bother to mention it in the BIOS setup program.

Note: It should be noted that this has nothing to do at all with the very similar sounding "32-bit disk access" and "32-bit file access" that are options within Windows 3.x. These have more to do with how Windows and its drivers function than anything to do with the hard disk itself.

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