Serial ATA technology, 4th edition

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support data packet retry because data packets can be very large (up to 8 KB) and the SATA interface would have
to buffer them for re-transmission.
Signal integrity
Serial architectures encode (embed) the clock signals in the data stream, eliminating the parallel bus skew problem
of aligning data and clock signals. Serial architectures reduce electrical noise because they have fewer data lines to
switch simultaneously and the low voltage reduces the effects of capacitance, inductance, and noise. As a result,
designers can increase serial signaling rates well beyond rates that are possible with a parallel bus.
Connectors and cabling
SATA uses an L-shaped 7-pin connector (four signal lines and three ground lines) and a small diameter cable up to
1m in length (Figure 4). The thin serial cable minimizes airflow resistance inside an enclosure and eases cable
routing. SATA also has a 15-pin, single-row power connector. The power connector provides optional hot-plug
capability, so you can swap out a drive without powering down the server. Servers with backplanes provide data
and power through the backplane connector.
Figure 4: SATA connections use a 7-pin data cable and 15-pin power cable.
SATA and SAS devices use a similar connector. The SATA device connector has a notch between data and power
pins (Figure 5), and the SAS device connector has a bridge between the data and power pins for a secondary data
port. The SATA host connector requires this notch, which prevents it from accepting SAS devices. SAS host
connectors can accept both SAS and SATA devices.