Hard Disk Speed Count

A hard disk’s performance depends on two things—speed of the hard disk and the interface with which it is connected to the rest of the PC. The speed of the hard disk is measured in rpm—rotations per second. That’s the number of rotations the spindle of the hard disk can complete within a minute. The speeds you will come across commonly are 5400 rpm and 7200 rpm. You can even get hard disks with speeds of 10000 rpm or more. For something as heavy duty as video editing while multitasking, you need 7200 rpm.

The speed of a hard disk also covers the data rate and the seek time. Data rate is amount of data that the drive can deliver to the processor in a second. Most hard disks deliver 5-40 MB per second. For video editing you should look for 10 MB/s. Seek time is the time the hard disk takes to get a file to the processor, once you have asked for it. It varies between 10-20 milliseconds. The shorter the seek time, the faster you see the file open up on screen. Hard disks with the same capacities but different rpms—say 5400 and 7200—will end up with different seek times also. The 7200 rpm drive would seek out files faster.

The interface also plays a huge part in determining the speed of a hard drive. A drive can use an IDE or a SCSI interface. Most desktop PCs use the IDE interface which has now two forms—Enhanced IDE and ATA. The most common IDE interface used in desktops today is UltraATA/133. If the hard disk has a cache to temporarily store data to speed up things, the name will have “Ultra” attached to it. The 133 in the name means that the transfer of data to and from the hard disk will happen at a speed of 133 MBps. You might get hard disks that use UltraATA/100—which may not be the best for your kind of applications. So be sure to ask the interface of the hard disk you are getting. The new interface in town is Serial ATA, and brings about a huge increase in performance, which also means higher cost. This starts at 150 MBps and is expected to touch 300 MBps next year. But this one is still finding its way to desktops, and is till quite expensive. It’s better to wait for at least six months.

Drives using the other interface, SCSI cost much more than IDE ones, and are better for multitasking. An SCSI controller has room for up to seven disks and even lets you place the disk outside the PC case. So SCSI is common in network servers. So unless your requirement is in that space, you don’t have to go the SCSI way.

Chris N Fernando