Hardware Reference
In-Depth Information
Figure 7.9. SATA Express motherboard and cable connectors, showing backward compatibility
with conventional SATA.
With SATA Express offering more than three times the throughput of conventional SATA, high-
performance storage devices like SSDs will become even faster in the future.
SATA Cables and Connectors
From
Table 7.9
, you can see that conventional SATA sends data only a single bit at a time, while
SATA Express sends 2 bits. The cable used for SATA has only seven wires (four signal and three
ground) and is a thin design, with keyed connectors only 14mm (0.55 inches) wide on each end. This
eliminates problems with airflow compared to the wider PATA ribbon cables. Each cable has
connectors only at each end, and each cable connects the device directly to the host adapter (typically
on the motherboard). There are no master/slave settings because each cable supports only a single
device. The cable ends are interchangeable; the connector on the motherboard is the same as on the
device, and both cable ends are identical. Maximum SATA cable length is 1 meter (39.37 inches),
which is considerably longer than the 18-inch maximum for PATA.
Although SATA-600 uses the same cables and connectors as the previous (slower) versions, it does
place higher demands for quality, so some manufacturers will mark higher quality cables with a rating
like “SATA 6Gbps.” One issue that becomes more of a problem is bending cables. Data moving at
the higher 3Gbps and 6Gbps rates can be corrupted when encountering a severe right-angle bend, so
it is recommended that when routing SATA cables you do not crimp or bend them sharply with a
pliers; use more gradual curves or bends instead. Note that this does not apply to cables with right-
angle connectors; the wires in the connectors have multiple bends or curve instead.
SATA uses a special encoding scheme called 8b/10b to encode and decode data sent along the cable.
IBM initially developed (and patented) the 8b/10b transmission code in the early 1980s for use in
high-speed data communications. Many high-speed data transmission standards, including Gigabit
Ethernet, Fibre Channel, FireWire, and others, use this encoding scheme. The main purpose of the
8b/10b encoding scheme is to guarantee that never more than four 0s (or 1s) are transmitted
consecutively. This is a form of Run Length Limited (RLL) encoding called RLL 0,4, in which the 0
represents the minimum and the 4 represents the maximum number of consecutive 0s or 1s in each
