Hardware Reference
In-Depth Information
To eliminate confusion over master/slave settings, most newer systems now use the cable
select option. This involves two things. The first is having a special PATA cable that has
allthewiresexceptpin28runningfromthemotherboardconnectortobothdriveconnect-
ors.Pin28isusedforcableselectandisconnectedtooneofthedriveconnectors(labeled
master)andnottotheother(labeledslave).Bothdrivesarethenconfiguredincableselect
mode via the CS jumper on each drive.
Withcableselect,thedrivethatreceivessignalsonpin28automaticallybecomesthemas-
ter, and the other becomes the slave. Most cables implement this by removing the metal
insulation displacement bit from the pin-28 hole, which can be difficult to see at a glance.
Other cables have a section of pin 28 visibly cut from the cable somewhere along the rib-
bon. Because this is such a minor modification to the cable and can be difficult to see,
cable select cables typically have the connectors labeled master, slave, and system, indic-
ating that the cable controls these options rather than the drive. All 80-conductor Ultra-
ATA cables are designed to use cable select.
With cable select, you simply set the CS jumper on all drives and then plug the drive you
want to be the master into the connector labeled master on the cable and the drive you
want to be the slave into the connector labeled slave.
The only downside I see to using cable select is that it can restrict how the cable is routed
or where you mount the drive that is to be master versus slave because they must be
plugged into specific cable connector positions.
PATA PIO Transfer Modes
ATA-2 and ATA-3 defined the first of several higher-performance modes for transferring
data over the PATA interface, to and from the drive. These faster modes were the main
part of the newer specifications and were the main reason they were initially developed.
The following section discusses these modes.
The PIO (programmed I/O) mode determines how fast data is transferred to and from the
drive using PIO transfers. In the slowest possible mode—PIO Mode 0—the data cycle
time can't exceed 600 nanoseconds (ns). In a single cycle, 16 bits are transferred into or
out of the drive, making the theoretical transfer rate of PIO Mode 0 (600ns cycle time)
3.3MBps, whereas PIO Mode 4 (120ns cycle time) achieves a 16.6MBps transfer rate.
Most motherboards with ATA-2 or greater support have dual ATA connectors on the
motherboard. Most of the motherboard chipsets include the ATA interface in their South
Bridge components, which in most systems is tied into the PCI bus.
