Hardware Reference
In-Depth Information
cessary. With 512 bytes per sector, this raises the maximum supported drive capacity to
144.12PB. That is equal to more than 144.12 quadrillion bytes! Note that the 48-bit ad-
dressing is optional and necessary only for drives larger than 137GB. Drives 137GB or
smaller can use either 28-bit or 48-bit addressing.
ATA/ATAPI-7 (ATA with Packet Interface-7)
Work on ATA-7, which began late in 2001, was completed and officially published in
2004. As with the previous ATA standards, ATA-7 is built on the standard that preceded it
(ATA-6), with some additions.
The primary additions to ATA-7 include the following:
• Ultra-DMA (UDMA) Mode 6 was added. This allows for 133MBps transfers (called
UDMA/133
,
Ultra-ATA/133
, or just
ATA/133
). As with UDMA Mode 5 (100MBps)
and UDMA Mode 4 (66MBps), the use of an 80-conductor cable is required.
• Added support for long physical sectors. This allows a device to be formatted so that
there are multiple logical sectors per physical sector. Each physical sector stores an
ECC field, so long physical sectors allow increased format efficiency with fewer ECC
bytes used overall.
• Added support for long logical sectors. This enables additional data bytes to be used
per sector (520 or 528 bytes instead of 512 bytes) for server applications. Devices us-
ing long logical sectors are not backward compatible with devices or applications that
use 512-byte sectors, such as standard desktop and laptop systems.
• SATA incorporated as part of the ATA-7 standard.
• The ATA-7 document split into three volumes. Volume 1 covers the command set and
logical registers, Volume 2 covers the parallel transport protocols and interconnects,
and Volume 3 covers the serial transport protocols and interconnects.
Note that although the throughput has been increased from the drive controller (on the
drive) to the motherboard via the UDMA modes, most ATA drives—even those capable
of UDMA Mode 6 (133MBps) from the drive to the motherboard—still have an average
maximum sustained transfer rate while reading data of under 60MBps. This means that
although newer ATA drives can transfer at speeds up to 133MBps from the circuit board
on the drive to the motherboard, data from the drive media (platters) through the heads to
the circuit board on the drive moves at less than half that rate. For that reason, running a
drive capable of UDMA Mode 6 (133MBps) on a motherboard capable of only UDMA
Mode 5 (100MBps) really doesn't slow things down much, if at all. Likewise, upgrading
your ATA host adapter from one that does 100MBps to one that can do 133MBps won't
help much if your drive reads data off the disk platters at only half that speed. Always re-
