Software keeps hard disk humming

Personal computer

January 21, 1991|By Michael J. Himowitz HTC | Michael J. Himowitz HTC,Evening Sun Staff

IF YOU OWN A CAR, you know what happens when you neglect little things like tuneups.

Performance starts to deteriorate, so slowly at first that you hardly notice it. But after a while, the car doesn't go as fast up hills. It gets noisy, and pulling onto the expressway in traffic becomes an act of courage. Eventually, it may not start at all.

Your computer can stand an occasional tuneup, too.

Its main moving part, the hard disk, may be the most important part of your machine. It's where you store your programs and data files, which is reason enough to keep it healthy.

But many of today's complex programs, such as Microsoft Windows, also use the hard disk as a substitute for extra memory. The faster and more efficient your disk, the better your programs perform. Fortunately, you don't have to take your hard disk to a mechanic for a tuneup. With the right software, you can keep it humming without ever seeing the inside of your computer.

Some programs, such as PC Tools Deluxe Version 6 (Central Point Software, $149.95) and The Norton Utilities (Symantec Corp., $149.95) are all-purpose tool-boxes that enhance disk performance, repair damaged files, recover deleted files and perform a variety of tricks.

Others, such as SpinRite II (Gibson Research Corp., $79.95) and Disk Optimizer Tools (Soft Logic Solutions, $69.95), are more specialized.

In general, they address three different factors that affect hard disk performance.

The first is low-level formatting, the process by which your disk controller inscribes the magnetic track and sector designators that your drive uses to locate each byte of data on the disk.

Today, this low-level formatting is typically done at the factory. When you install DOS, the disk operating system, it applies higher-level formatting that organizes your disk into DOS's own particular filing scheme.

After you've used your disk awhile, the read-write heads can drift a little bit (we're talking about thousandths of an inch here, but in the miniature world of computers, a thousandth of an inch can be a lot).

As a result, the computer can lose track of low-level formatting information and create errors when it reads and writes data. DOS corrects small errors without help, but over time, problems with low-level formatting can render a disk unusable.

SpinRite II specializes in correcting this problem, although PC Tools and Norton now have similar utilities.

Typically, they examine each byte on the disk, perform thorough read-write tests and create a new low-level format. Depending on the size of the job and how thoroughly you want to test, the process can take anywhere from 10 minutes to five or six hours.

If you can't afford that much down time, most low-level formatters allow you to break off in the middle of the job, use your PC normally, then take up the job in mid-stream.

Another problem that can make your drive run slow is an improper interleave setting. To understand this, consider that your hard dive is organized as a series of concentric circles called tracks or cylinders. Each cylinder is broken down into arcs called sectors.

On a perfectly efficient drive, the sectors are read consecutively. Sector 1 is physically located next to Sector 2, and so forth. This is called a 1-to-1 interleave.

Unfortunately, not all computers can handle data transfers that quickly. If a computer can't read or write data quickly enough to match the interleave, it has to wait until the disk spins a full revolution to catch the next logical sector. This can slow performance considerably.

As a result, early IBM-XT compatibles came with drives that had a 3-to-1 interleave. This meant that Sector 1 and Sector 2 were actually three sectors apart. With this spacing, the disk controller and central processor could keep up with the flow of data without waiting a full revolution.

As computers got faster, drive manufacturers often didn't change the interleave to match processor and disk controller speed. So the computers with disks set for 3-to-1 interleaves weren't performing up to capacity.

SpinRite was one of the first programs to change this interleave without requiring that the drive be completely reformatted. It determines the proper setting for your system and changes it automatically.

Other utilities now have the same feature. If you have an older AT-style computer with an 80286 processor, you may well have a hard drive that could run much faster with a tighter interleave. The first time I ran SpinRite on my old AT machine, I couldn't believe the difference in performance.

The third villain in disk performance is file fragmentation. When you write a letter to Aunt Rhoda and save it on your hard disk, DOS doesn't always write it as one long stream of data.

The operating system grabs the first free block of space it can find and starts writing. If that isn't enough, DOS grabs the next free chunk, even if it's somewhere else on the disk.

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