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Serial ATA
Last updated: 9/8/01
Q. What is a Serial ATA disk drive?
 To
put it in a nutshell, the ATA Serial standard is a simplified packet switching
network between a motherboard or computer backplane and a disk drive. It
employs balanced voltage (differential) amplifiers and four wires/two pairs
(transmission line) to connect transmitters to receivers in a manner similar
to the 100BASE-TX Ethernet. The pins in the spec are labeled TX+,
TX-, RX+, and RX- just like they are in the twisted-pair Ethernet. There
is no specification for a standard ATA Serial cable (just electrical requirements
it must meet), but each pair of wires will probably be parallel and shielded
(there is a cable construction example in the spec.). There is a separate
power cable. Here are some brief highlights of this recent technology:
- Scalable performance… Three stages
over ten years… Starts at 1.5 Gigabits per second, then 3 Gbps, and ultimately
6 Gbps (six times faster than the current ATA/100 standard). These
numbers are right in the spec.
- 100% software compatible with current
operating systems and does not require any new drivers/changes to existing
operating systems.
- Primarily for inside-the-box drive
connections. Maximum cable length is 1 meter. No cameras/scanners/printers.
- Supports all ATA and ATAPI devices,
including CDs, DVDs, tape
devices, high capacity removable devices, zip drives, and CD-RWs.
- Drives can be attached by cable or
plugged directly into backplanes.
- More reliable connectors with smaller
plugs and a lower pin-count.
- Plugs are blind mated (can plug them
in blindfolded without making an error).
- No drive jumpers or terminators, one
drive per cable, Plug ‘n Play (Prey?).
- Drives can be hot plugged—installed
with the computer on.
- Smaller cables (thin, flexible) that
are simple to route and install. The data cable has 4 conductors.
- Smaller cables will allow much better
case ventilation (and access/visibility).
- Less complex trace runs on motherboards;
will permit smaller motherboards.
- ATA Serial interface to be incorporated
into the motherboard chipsets.
- Favorable (low) voltages and efficient
power delivery.
- Power management and power consumption
suitable for mobile use.
- Light protocol minimizes overhead
latencies.
- Asynchronous only (no isochronous
requirements).
- No peer-peer transfer support (to/from
host only).
- Provides support for 1st party DMA
access to the host
Serial ATA drives and motherboards should begin to appear
in 2002. Motherboards will probably include old ATA and serial interfaces
for a while to accommodate older drives. Serial ATA should be cost-competitive
with equivalent parallel ATA solution at introduction.
Serial
ATA Disk Drive Specification
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