Hardware Reference
In-Depth Information
auxiliary interface to ATA but merged completely within it. Thus, ATA-4 promoted ATA for use as
an interface for many other types of devices. ATA-4 also added support for new Ultra-DMA modes
(also called Ultra-ATA) for even faster data transfer. The highest-performance mode, called
UDMA/33, had 33MBps bandwidth—twice that of the fastest programmed I/O mode or DMA mode
previously supported. In addition to the higher transfer rate, because UDMA modes relieve the load
on the processor, further performance gains were realized.
An optional 80-conductor cable (with cable select) is defined for UDMA/33 transfers. Although this
cable was originally defined as optional, it would later be required for the faster ATA/66, ATA/100,
and ATA/133 modes in ATA-5 and later.
Support for a reserved area on the drive called the HPA was added via an optional
SET MAX
ADDRESS
command. This enables an area of the drive to be reserved for recovery software.
Also included was support for queuing commands, similar to those provided in SCSI-2. This enabled
better multitasking as multiple programs request ATA transfers.
Another standard approved by the T13 committee in 1998 was “ANSI NCITS 316-1998 1394 to AT
Attachment - Tailgate,” which is a bridge protocol between the IEEE 1394 (i.LINK/FireWire) bus
and ATA that enables ATA drives to be adapted to FireWire. A tailgate is an adapter device
(basically a small circuit board) that converts IEEE 1394 (i.LINK or FireWire) to ATA, essentially
allowing ATA drives to be plugged into a FireWire bus. This enabled vendors to quickly develop
IEEE 1394 (FireWire) external drives for backup and high-capacity removable data storage. Inside
almost any external FireWire drive enclosure you will find the tailgate device and a standard ATA
drive.
See the
Chapter 14
section, “
IEEE 1394 (FireWire or i.LINK)
,
”
p.
718
.
ATA/ATAPI-5 (ATA with Packet Interface-5)
ATA-5 was built on the previous ATA-4 interface. ATA-5 includes Ultra-ATA/66 (also called
Ultra-DMA
or
UDMA/66
), which doubles the Ultra-ATA burst transfer rate by reducing setup times
and increasing the clock rate. The faster clock rate increases interference, which causes problems
with the standard 40-pin cable used by ATA and Ultra-ATA. To eliminate noise and interference, the
newer 40-pin, 80-conductor cable was made mandatory for drives running in UDMA/66 or faster
modes. This cable adds 40 additional ground lines between each of the original 40 ground and signal
lines, which helps shield the signals from interference. Note that this cable works with older, non-
Ultra-ATA devices as well because it still has the same 40-pin connectors.
Work on ATA-5 began in 1998, and the standard was finished and officially published in 2000 as
“ANSI NCITS 340-2000, AT Attachment - 5 with Packet Interface.”
The major additions in the ATA-5 standard include the following:
• Ultra-DMA (UDMA) transfer modes up to Mode 4, which is 66MBps (called UDMA/66 or
Ultra-ATA/66).
• The 80-conductor cable now mandatory for UDMA/66 operation.
• Automatic detection of 40- or 80-conductor cables.
• UDMA modes faster than UDMA/33 enabled only if an 80-conductor cable is detected.
The 40-pin, 80-conductor cables support the cable select feature and have color-coded connectors.
The blue (end) connector should be connected to the ATA host interface (usually the motherboard).
