Hardware Reference
In-Depth Information
on the ROM BIOS for support and use OS-managed drivers instead.
Operating System Limitations
More recent OSs, such as Windows Vista and Windows 7/8, don't have problems with larger drives.
However, older OSs might have limitations when it comes to using large drives.
Windows XP and earlier versions are limited in capacity to supporting drives less than 2.2TB per
physical or logical (that is, RAID) drive, including all partitions. This is due to reliance on the MBR
partitioning scheme, which uses 32-bit sector numbering, limiting a physical or logical drive to a
maximum of 2
32
(4,294,967,296) total sectors. Windows 7/8 and Vista SP1+ support a newer
partitioning scheme called GPT, which defines sectors using 64-bit numbers, supporting 2
64
(18,446,744,073,709,551,616) sectors, for a maximum capacity of 9.44ZB (zettabytes or billion
terabytes). In practical terms, this means that if you are running XP, you can't normally utilize more
than 2TB of a single drive or a RAID array of multiple drives. However, Windows XP can use GPT
formatted drives of 2.2TB or greater in capacity if a third-party GPT utility tool like the Paragon GPT
Loader (
www.paragon-software.com
) is used.
Performance
When you select an HDD, one of the important features you should consider is the performance
(speed) of the drive. Hard drives can have a range of performance capabilities. As is true of many
things, one of the best indicators of a drive's relative performance is its price. An old saying from the
automobile-racing industry is appropriate here: “Speed costs money. How fast do you want to go?”
The speed of a disk drive is typically measured in two ways:
• Transfer rate
• Average access time
Transfer Rate
The transfer rate is probably more important to overall system performance than any other statistic,
but it is also one of the most misunderstood specifications. The problem stems from the fact that
several transfer rates can be specified for a given drive; however, the most important of these is
usually overlooked.
Don't be fooled by interface transfer rate hype, especially around ATA-133 or SATA-150/300/600.
A far more important gauge of a drive's performance is the average media transfer rate, which for a
hard disk is significantly lower than the interface rate of 133, 150, 300, or 600MBps. Solid-state
drives (SSDs), on the other hand, are often limited by the interface transfer rate, and for maximum
performance current SSDs require the full 600MBps that SATA revision 3 6Gbps ports can provide.
On a hard disk the media transfer rate represents the average speed at which the drive can actually
read or write data. By comparison, the interface transfer rate merely indicates how quickly data can
move between the motherboard and the buffer on the drive. The rotational speed of the drive has
perhaps the biggest effect on the drive's true transfer speed; in general, drives that spin at 10,000 rpm
transfer data faster than 7,200 rpm drives, and 7,200 rpm drives transfer data faster than those that
spin at 5,400 rpm. Note, however, that rotational speed is not the only thing to consider—the track
linear density plays a huge part in performance as well. For example, the 5,400 rpm 500GB drive in
one of my laptops has a maximum transfer rate of 118MBps, whereas the 7,200 rpm 60GB drive in an
older laptop has a maximum transfer rate of only 44MBps. That means my newer 5400 rpm drive is
