Intel 815 - Manual (Page 113)

I/O Subsystem
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Intel
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815 Chipset Platform Design Guide 113
10.2 Cable Detection for Ultra ATA/66
An 80-conductor IDE cable is required for Ultra ATA/66. This cable uses the same 40-pin
connector as the old 40-pin IDE cable. The wires in the cable alternate: ground, signal, ground,
signal,. . . . All ground wires are tied together on the cable (and they are tied to the ground on the
motherboard through the ground pins in the 40-pin connector). This cable conforms to the Small
Form Factor Specification SFF-8049, which is obtainable from the Small Form Factor
Committee.
To determine whether the ATA/66 mode can be enabled, the chipset using the ICH requires the
system BIOS to attempt to determine the type of cable used in the system. The BIOS does this in
one of two ways:
•
Host-side detection
•
Device-side detection
To determine whether the ATA/66 mode can be enabled, the ICH requires that the system software
attempt to determine the type of cable used in the system. If the system software detects an 80-
conductor cable, it may use any Ultra DMA mode up to the highest transfer mode supported by
both the chipset and the IDE device. If a 40-conductor cable is detected, the system software must
not enable modes faster than Ultra DMA Mode 2 (Ultra ATA/33).