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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.
Next: Block Mode