What to Look for in a New Hard Disk

Last week, my colleague, Richard O’Reilly, wrote about software to compress files on your hard disk. Compression software, as he pointed out, is a relatively inexpensive way to increase the amount of data you can store on your hard disk.

However, it’s not the best solution in all cases. Compression software uses up random access memory, which may not be available if you use other memory resident software. It can also slow down the drive’s performance. Finally, many people feel uneasy about the idea of compressing their data, fearing that it’s one more thing that could possibly go wrong.

For some users, a new hard disk is a better solution. The good news is that it’s usually possible to add a second drive without removing the first or even buying a new controller card. Some more good news is that hard disks, like most computer equipment, have steadily dropped in price. In 1982, hard disks cost about $300 per megabyte. Today, you can buy a 100-megabyte (or larger) hard disk for less than $3 a megabyte.

You must be sure, however, that the drive you buy is compatible with the rest of your equipment. If your IBM-compatible computer is an older-style 8088 or 8086-type system, you’ll need a drive that uses an RLL or MFM interface. Most of today’s computers now come with IDE drives, sometimes referred to as “AT-standard.” IDE stands for “integrated drive electronics” because the controller mechanism is built into the drive itself. IDE drives require a machine with a 286 or higher CPU. Usually, the drive is connected to the PC via an IDE adapter board that’s plugged into one of the machine’s expansion slots. A typical IDE board can support up to two hard disks and two floppy drives.

SCSI (or Small Computer System Interface) is the standard for the Macintosh. Its main advantage is that you can connect up to seven devices to a single SCSI port. Mac users are accustomed to “daisy chaining” multiple disk drives, CD-ROM players, scanners and even printers to the Mac’s one external SCSI port. Thanks to the SCSI interface, installing an external Macintosh hard disk can be as easy as plugging in a cable.

Most PCs don’t come with a SCSI interface, but a number of companies, including Western Digital and Future Domain, make add-in SCSI adapters. Trantor Systems of Fremont, Calif., (510) 770-1400, makes a portable SCSI adapter that plugs into the parallel port of any PC, including notebook and laptop models.

Unfortunately, a SCSI standard for IBM compatibles has not emerged to the point where you can buy off-the-shelf SCSI devices with the assurance that they’ll work together. For now, SCSI is a reasonable option, but it’s not always cost effective. For most users, IDE remains a better value.

Most IBM-compatible drives are designed to be installed inside the machine. If you have some space available, you’ll still need the skill and patience to install the drive. It can be tricky, so you might want to leave it to a dealer or technician.

If you’re willing to spend a little more money for an easy solution, get a Plus HardCard, from Quantum, (800) 624-5545. It’s easy to install because both the disk controller and the drive itself are mounted on a single plug-in card. Suggested retail prices range from $389 for 50 megabytes to $569 for 105 megabytes. Street prices should be less.

There are several ways to report the speed of a hard disk, but the most common number is the average access time it takes for the read/write head to move from one random spot on the disk to another. That time, measured in milliseconds, can be anywhere from nine milliseconds to more than 100. The lower the number, the faster the drive.

The hard disks in high-performance machines, such as those with the 386 or 486 CPU, tend to perform in the range of 14 to 24 milliseconds. Another performance index, called data transfer rate, measures the number of kilobytes that can be transferred per second.

Today’s hard disks, though very reliable, are not invincible. Manufacturers generally rate their drives in terms of “mean time between failures” (MTBF). The number given is a projected statistical average--sort of like life expectancy.

Many of today’s drives are rated for 150,000 hours--or more than 17 years of consecutive use. But then again, they could die the first day or run for more than a million hours.

It’s all speculation, of course, because the personal computer industry hasn’t even been around for 150,000 hours.