One of the most frequent complaints I get from people who bought computers two or three years ago is that they're out of disk space.

Many of those machines came with 40- or 80-megabyte hard drives, which seemed copious at the time but are now bulging with the bloated programs and data files that software publishers insist that we need. Today's low-end machines typically come with 170- or 200-megabyte drives, but even those can fill up quickly.

Although I'm accustomed to rapid changes in technology, this explosion in disk space -- and disk requirements -- still amazes me.

The first computer I bought 11 years ago didn't have a disk drive at all. It stored programs and data on a cassette recorder, which had the advantage of being cheap but the disadvantage of being outrageously slow and not at all reliable.

When I saved up my money and bought a floppy disk drive (about $450 at the time), I thought I'd died and gone to heaven. Each one of those floppy disks held 150K of data. I figured I'd never fill up more than a few of them.

A few hundred floppies and a couple of computers later, I was ready for a hard disk drive. This time, the same $450 bought an incredible 20 megabytes of storage. I knew I'd never come close to filling that one up. After all, in those days the average word processing program came on two or three low-density, floppy disks.

Wrong again. Within a year, I added another 20-megabyte hard drive. When that filled up, I swapped one of the 20-meg drives for a 40-megabyte drive, and then I replaced the remaining 20-megabyte drive with an 80-megabyte model (which also cost about $450, as I recall).

I won't bother you with more details other than to say that joining PackRats Anonymous didn't help. I'm hopeless. But while I undoubtedly demand more than the average user, buyers should be aware that even with prudent management, today's huge hard drive may be tomorrow's overflowing closet.

Let's take a look at a typical IBM-compatible computer used by mom and dad for business and by the kids for homework, educational software and a couple of games.

First, DOS itself occupies 6.5 megabytes, and Microsoft Windows grabs 13 more. Since we want to keep our computer tuned up and safe from viruses and disk failures, we'll add PC Tools for Windows, another 15 megs. That cute little screen saver from After Dark? A mere 5.7 megs. That's about 40 megabytes of drive space consumed, and all we can do is play solitaire.

Add basic muscle

Let's add some basic muscle -- a word processor, spreadsheet and data base. Lotus AmiPro, the word processor I use, checks in at 18 megabytes, while Lotus 1-2-3 for Windows takes up 9 megs and Borland's Paradox data base claims another 15. To handle the family finances we'll add the popular Quicken for Windows, at 5.4 megabytes, and we'll do the family and business taxes with TaxCut, at 7.5 megabytes.

Since we're hitching a ride on the information highway, we'll need a communications program (Procomm Plus for Windows, 4.4 megabytes), and maybe a subscription to Prodigy (2.8 megabytes). The kids love to do their party invitations on the computer, so we'll add Print Shop Deluxe, at 7 megabytes. Mom and dad have always wanted to catalog their recipe collection, so we'll add Micro Cookbook for Windows, another 7 megabytes.

Since we justified spending two grand on this computer by saying it would help the kids at school, we bought Microsoft's Encarta encyclopedia on CD-ROM. You say that shouldn't occupy any hard disk space? Guess again. While CD-ROM programs keep their huge data bases on the CD, to run at acceptable speed they have to park their program and index files on your hard disk. Encarta wants 6 megabytes.

Did the kids love Oregon Trail at school? It stakes out a 4.4-megabyte homestead on your PC. Want your children to learn about dinosaurs and managing a business at the same time? Dino Park Tycoon takes up 6 megs. The Mario Brothers want 3.3 megs to teach the youngsters how to type. That cute little Reader Rabbit wants a 5-megabyte cabbage patch, and Carmen Sandiego, the beloved international thief, will steal 8 megs while your back is turned.

Are you counting? We haven't had any real fun yet. Let's add baseball and hockey for the younger kids (2.8 and 9.6 megs, respectively), with some good adventure games such as Master of Orion and Darklands (31 megabytes total) for the older ones. And dad always wanted to pilot that MiG/-29. All it needs is a 9-megabyte landing strip.

So there you have it. Your basic home and small business PC, with just over 188 megabytes of hard disk space occupied before we've done anything useful. No wonder that old 80-megabyte drive seems so crowded.

What can you do about it? One option is disk compression software, which can effectively increase the capacity of your hard disk by 50 to 80 percent. Stacker is the most popular third-party compression software, and Microsoft should soon XTC have a version of DOS with its own compression program, replacing the Double Space software it had to abandon when it lost a patent infringement suit to Stacker's publisher.

Another option

A second option is adding another hard disk, and there's good news here. If you have a free internal drive bay, you can probably add a second drive to your system without much hassle. And storage is cheap. A 250-megabyte drive retails for less than $250, while for $450 (the price of my original floppy disk drive), you can add up to 540 megabytes of space.

Strictly speaking, adding a disk drive can be a do-it-yourself project, but so is replacing a toilet. With either one, you'd better know what you're doing. If you're not comfortable crawling around in your PC, get a good service department to do it. You'll pay $50 to $100, but it's well worth the price.

In case you're wondering, my current PC has three drives. With disk compression software, they can store about 800 megabytes of data. Right now, I have about 100 megabytes of free space. I figure it will last six months.

Michael J. Himowitz is a staff writer for The Baltimore Sun.