Hardware Reference
In-Depth Information
As you can see, the
true
transfer rates for these drives are much lower than the 300MBps
SATA interface transfer rate. Although all these support the 3Gbps (300MBps) SATA
transfer rate specification, they have media transfer rates of up to 160MBps maximum,
withindividualdrivesaveragingbetweenabout80MBpsand120MBps.Notethatthefast-
est performing drive is not the fastest rotating drive because density has as much or more
to do with actual performance as rotational speed does.
Two primary factors contribute to transfer rate performance: rotational speed and the lin-
ear recording density or sector-per-track figures. When you're comparing two drives with
thesamenumberofsectorspertrack,thedrivethatspinsmorequicklytransfersdatamore
quickly.Likewise,whenyou'recomparingtwodriveswithidenticalrotationalspeeds,the
drive with the higher recording density (more sectors per track) is faster. A higher-density
drive can be faster than one that spins faster—both factors have to be taken into account.
As you can see from these examples, the interface transfer speed is almost meaningless.
So, if you were thinking about getting a new motherboard or maybe a separate host ad-
apter card offering a faster interface rate for the sole purpose of increasing drive perform-
ance, save your money. To be fair, there will be a slight benefit to higher interface trans-
fer speeds in that data from the buffer on the drive controller can be transferred to the
motherboard at interface speed, rather than media speed. These buffers are usually 32MB
or less and help only with repetitive transfers of small amounts of data. However, if you
perform repetitive transfers frequently, drives with larger buffers can improve perform-
ance with applications that perform repetitive transfers. More recently, drives with large
Flash memory buffers, called
hybrid
drives, are being manufactured to improve perform-
ance for startup and commonly read files. These drives offer near SSD read performance
while costing only a little bit more than standard drives.
Allotherthingsbeingequal,adrivethatspinsfastertransfersdatafaster,regardlessofthe
interface transfer rate. Unfortunately, it is rare that all other things are exactly equal, so
you should consult the drive specifications listed in the data sheet or manual for the drive
to be sure.
When evaluating drive performance, don't just compare one specification, such as inter-
face speed or rotational speed, because these can be misleading. The interface speed is
