Hardware Reference
In-Depth Information
3) require additional or updated drivers to fully exploit these faster modes. Contact the
motherboard or system vendor for the latest drivers.
For reliability, Ultra-DMA modes incorporate an error-detection mechanism known as
cyclical redundancy checking
(CRC). CRC is an algorithm that calculates a checksum
usedtodetecterrorsinastreamofdata.Boththehost(controller)andthedrivecalculatea
CRCvalueforeachUltra-DMAtransfer.Afterthedataissent,thedrivecalculates aCRC
value, and this is compared to the original host CRC value. If a difference is reported, the
host might be required to select a slower transfer mode and retry the original request for
data.
ATA/ATAPI-6 (ATA with Packet Interface-6)
ATA-6 includes Ultra-ATA/100 (also called
Ultra-DMA
or
UDMA/100
), which increases
theUltra-ATAbursttransferratebyreducingsetuptimesandincreasingtheclockrate.As
with ATA-5, the faster modes require the improved 80-conductor cable. Using the ATA/
100 mode requires both a drive and motherboard interface that supports that mode.
Work on ATA-6 began in 2000, and the standard was finished and officially published in
2002 as “ANSI NCITS 361-2002, AT Attachment - 6 with Packet Interface.”
The major changes or additions in the standard include the following:
• Ultra-DMA (UDMA) Mode 5 added, which allows 100MBps (called
UDMA/100
,
Ultra-ATA/100
, or just
ATA/100
) transfers.
• Sector count per command increased from 8 bits (256 sectors, or 131KB) to 16 bits
(65,536 sectors, or 33.5MB), allowing larger files to be transferred more efficiently.
• LBA addressing extended from 2
28
to 2
48
(281,474,976,710,656) sectors, supporting
drives up to 144.12PB (petabytes = quadrillion bytes). This feature is often referred
to as
48-bit LBA
or
greater than 137GB support
by vendors; Maxtor referred to this
feature as
Big Drive
.
• CHS addressing was made obsolete; drives must use 28-bit or 48-bit LBA addressing
only.
Besides adding the 100MBps UDMA Mode 5 transfer rate, ATA-6 extended drive capa-
city greatly, and just in time. ATA-5 and earlier standards supported drives of up to only
137GB in capacity, which became a limitation as larger drives were becoming available.
Commercially available 3 1/2-inch drives exceeding 137GB were introduced in 2001, but
they were originally available only in SCSI versions because SCSI doesn't have the same
limitations as ATA. With ATA-6, the sector addressing limit has been extended from 2
28
sectors to 2
48
sectors. What this means is that LBA addressing previously could use only
28-bit numbers, but with ATA-6, LBA addressing can use larger 48-bit numbers if ne-
