FEATURE / ANALYSIS
Storage interfaces
Aside from USB, perhaps the second most
famous example of the large-scale switch
from parallel interfaces to modern, high-
speed serial interfaces is SATA. Literally
standing for serial ATA, SATA was introduced
back in 2000 as a new serial interface for
storage devices, replacing the PATA (parallel
ATA, or IDE) interface used before.
Like other modern serial interfaces, its
primary advantages were faster data rates, its
native hot-swapping ability and reduced cable
size and cost. Whereas PATA cables used
either 40 or 80 conductors, SATA uses just
seven, with two LVDS pairs for bi-directional
data transfer, and three ground wires that
sit either side of and in between the two
data pairs.
However, while we’ve seen the likes of
USB and PCI-E evolve and adapt to the
ever-increasing demands for shifting data,
SATA has been left behind in the face of
a very different data storage landscape.
Fundamentally, despite all its advantages
ove r PATA , S ATA i s s t i l l a r e l a t i ve ly s l ow
standard compared with PCI-E, as it can’t
take advantage of multi-lane parallelism.
A drive has a single SATA cable and that’s it.
Meanwhile, SSDs have become faster
and faster, precisely because they’ve taken
advantage of parallelism. Just as with RAM,
the real speed advantage of modern SSDs
isn’t just in the solid state nature of their data
access, but in the fact that a drive will contain
multiple banks of chips across which it can
share the read and write workload. As such,SSD speed has skyrocketed and, without
an interface that can take advantage of
that performance, SSD speed is drastically
held back.
The solution has been for SSDs to switch
to a different standard of data access, namely
PCI-E. While modern SSDs may plug into
an M.2 slot and communicate using the
new NVMe software protocol, the interface
underlying this setup is PCI-E. An M.2 slot is
just a physical access point for up to a four-
lane PCI-E interface, in just the same way as a
traditional 4x PCI-E slot. Indeed, that’s why for
a while, the fastest SSDs were on PCI-E cardsThe future
Looking to the future of the PC, most of the
trends for the near future are already clearMini-ITX
motherboards
and cases are
all most of us need
these days, but many
of us still opt for larger
form factors