Ed T Wilson said:
A colleague of mine has advised that the current state-of-the-art
chipsets supporting AMD XP processors will not provide any performance
advantage over a UDMA 133 IDE hard drive. Hence, buying a SATA hard
drive for my A7N8X would be a waste of money. Is that correct?
Thanks for the help.
The current state of affairs has less to do with the AMD versus Intel
thing, than it has to do with bus architecture. A PC has a series of
busses chained together, each one tuned to the needs of the peripherals
that are connected to it. The fastest bus is the one between the
Processor and the Northbridge, and is capable of tremendous bandwidth.
Depending on the generation of chipset, the bus between the Northbridge
and Southbridge is slower, and generally has enough bandwidth to handle
the bridge to PCI bus on the Southbridge (older chipsets use PCI
starting from the Northbridge, and the Southbridge is just another
peripheral - that is the older way of doing it).
We still live in an era, where for the most part, onboard peripherals
that have I/O connectors on the back of the computer, are connected
to the PCI bus. PCI busses come in several speeds, and for desktop
systems, PCI is still 32 bits bus width, with a maximum (theoretical)
bus bandwidth of 133MB/sec. A reasonable real world bandwidth figure
for PCI is 100MB/sec (bus mastering, fairly small burst size, in order
to allow sharing of the bus without causing another card to be starved).
Now, look at SATA. The cable used on SATA transfers data at 150MB/sec.
Sounds like a great deal, a little faster than the best PATA can do.
The current generation of disk drives use a bridging chip, to convert
from PATA on the disk drive controller board, to the SATA serial way
of doing things. I think a review I read mentioned that some of the
bridge chips are limited to ATA100 parallel rates, so that is a
limitation at the disk end. Eventually, there will be SATA native
controllers on disk drives, in which case the bridge chip will
disappear, and more of the potential of the SATA cable can be used.
Whether it is in the best interest of the disk drive manufacturer,
to make it work at the full 150MB/sec max rate, is something we'll
know when native drives become available. This rate is only useful
for bursting data into the disk drive cache, as the sustained media
rates are still well below the 150MB/sec figure.
At the other end of things, we have the SATA controller on the
motherboard. If your board has a SIL3112 controller, it is connected
to the PCI bus, so the controller itself is limited to the approx
100MB/sec max transfer rate across PCI. So, for a chip like this,
even if you buy a native drive in a year's time, the max burst
rate is still not going to be any better, due to the PCI bus.
Many SATA chips support two drives, for a theoretical maximum of
300MB/sec. For motherboard chipsets that have SATA built in, there
is the potential to connect them to an internal bus, which is
running faster than the current PCI. So, when shopping, you
need to check whether the SATA on the motherboard comes from the
Northbridge or the Southbridge, and if it does, is it connected
to a faster internal bus. An example of a faster bus, is the
266MB/sec CSA bus on an Intel 875P. This kind of architecture
allows peripherals with a faster transfer rate than ordinary PCI
to work at closer to their potential.
Many architectural changes are coming to PC motherboards, and
there will be havoc as these changes are introduced (the havoc is
necessary to break free of the chicken versus egg issues of
advancing past 133MB/sec PCI). It is hard to offer advice on
which options are the best ones to bet on. Having any SATA
interface, even if it is a little inferior, will be necessary
for the day that parallel interface drives are no longer being
sold everywhere. So, I wouldn't lose any sleep over the current
limited implementations, as the main value of a SATA interface is
it helps ensure you can buy a new drive in a few years for your
"aged" motherboard.
Think of SATA right now as compatibility insurance, rather than
as a performance thing. SATA will become faster in the future,
at which point there will be a performance advantage, assuming
that someone builds a disk drive with higher media rates. But,
by that time, so many other things will have changed in the PC,
you'll be buying another motherboard anyway.
HTH,
Paul
