UPGRADING REPAIRING PCs

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Chapter 4—SCSI and IDE Hard Drives and Optical Drives
modes 3 and above require a local-bus connection—either VL-Bus,
PCI card, or (most often) a PCI motherboard connection.
The first ATA-2/EIDE hard drives introduced in 1994 were capable
of PIO 3 transfer rates, but newer drives run at PIO 4 transfer rates
or above. Most recent BIOSs detect the correct PIO mode as well as
the basic drive geometry and set it for you. On BIOSs that offer a
PIO mode setting that you must make manually, consult the drive
vendor for the correct mode. Setting the PIO mode too high will
cause data corruption.
Ultra DMA
The newest hard drives and motherboards support an even faster
method of data transfer called Ultra DMA, or UDMA for short. See
Table 4.11 for common Ultra DMA modes.
Table 4.11 Common Ultra DMA Modes
Transfer Rate
UDMA Mode (MB/Sec) Specification
2 33.33 ATA-4, Ultra-ATA/33
4 66.67 ATA-5, Ultra-ATA/66
5 100.00 Ultra-ATA/100
With both PIO and UDMA modes, the transfer rates listed are maximum
(burst) transfer rates; sustained rates are much slower.
Nevertheless, you will want to run your hard disk at the highest PIO
or UDMA mode it’s capable of.
UDMA/66 and UDMA/100 Issues
Most of the greater-than-10GB hard drives now on the market are
designed to support UDMA/66 (also called Ultra ATA-66) if certain
requirements are met; many larger drives also support the even faster
UDMA/1000 standard introduced in the summer of 2000. Table 4.12
lists the requirements for UDMA/66 and UDMA/100 compliance.
Table 4.12 Ultra DMA/66 and UDMA/100 Requirements
Item Features Notes
Drive Drive must have firmware Some drives automatically sense
for desired mode. compliance; others require you to
run a configuration program to
enable the mode; consult drive
vendor.
Motherboard Must have UDMA/66 Check system or MB vendor for
chipset or UDMA/100 support. compliance; for highest performance,
you should also install an
UDMA device driver for operating
system (see Table 4.13).