Windows workshop. (IBM DOS 6.0's DoubleSpace) (Software Review) (Evaluation)
by Clifton Karnes

Last month, I promised to talk about DOS 6's DoubleSpace, especially as it compares to Stac Electronics' Stacker. I've been using Stacker since version 1.0, and it's always performed flawlessly. I have to admit that I was a little queasy about trying a new compression product, but I wanted to test DoubleSpace and compare it with Stacker, so I decided to give it a try.

For Stacker users, Micro-soft has a $10 product that will convert a Stacker-compressed volume to a DoubleSpace one (there's a coupon in your DOS manual). I had hoped to use that product to convert my Stacker drive to a DoubleSpace drive, but it didn't arrive in time, so I did the conversion the hard way.

Here's the procedure I followed: I backed up my hard disk to tape, reformatted the disk, installed DoubleSpace, and restored the tape backup, it was not quite as simple as this sounds, but that's the gist of it. Since I wanted to run some benchmarks on my Stacker volume before I reformatted, I first optimized the Stacker drive and ran my database benchmarks and a suite of Windows programs. I ran each benchmark three times and averaged the scores.

Next, I backed up my hard disk. With Stacker, my hard drive is about 400MB, and the backup took about two hours. Then I created a DOS 6 bootable floppy and reformatted my hard disk with the /s option to make the disk bootable.

Before I could install DoubleSpace, I needed to restore all the files I use that create virtual drives, because these need to be active when DoubleSpace runs so it can intelligently choose a drive letter for itself. This meant that I had to reinstall my network files so the network drives would be available. I had to run Windows and build a permanent swap file, because after DoubleSpace was installed, this would not be possible. And I had to restore all my CD-ROM software so the CD-ROM drives could be installed.

After these files were restored, I booted up DOS (with its CD-ROM drives) and logged on to the network. Next, I ran DoubleSpace and followed the onscreen instructions to build a compressed volume. DoubleSpace works like Stacker in that it creates a compressed drive that in reality is a hidden system file on your physical drive. After the DoubleSpace (or Stacker) driver is installed, this file looks just like another drive to your computer. Traditionally, the real drive is called the physical drive, and the compressed drive is called the logical drive. This logical drive is, as mentioned above, really just a large file on your physical drive. After DoubleSpace installed itself, my drive C was a logical drive, and my physical drive became drive E.

Next, I restored the rest of my files (this took about four hours), and I was ready to go. I wanted to run my benchmarks using DoubleSpace, but just to be on the safe side, I optimized the DoubleSpace volume first and then ran the programs.

The results were about what I'd expected. DoubleSpace proved to be essentially as fast as Stacker (Stacker averaged 2 percent faster, which I consider insignificant), and it provided about the same compression ratio - 1.8 to 1.

I have been running DoubleSpace for about two months, and it's performed without a hitch.

For Windows users, DoubleSpace does two things. First, it gives you more disk space for disk-hungry Windows applications. Second, it lets you check on your free disk space and the compression ratio for any file or group of files from inside File Manager. If you click on the DoubleSpace icon or select Tools, DoubleSpace Info, you'll see a 3-D pie chart of your hard disk indicating free space. Click on More, and you'll see the compression ratio of the selected file or files. Pretty cool.

DoubleSpace has one big advantage over Stacker that I haven't discussed so far, and that's that the driver is loaded before your system runs CONFIG.SYS. This means that with DoubleSpace there's no more problem synchronizing CONFIG.SYS and AUTOEXEC.BAT files on both your logical and physical volumes (usually drives C and D, respectively). The next version of Stacker should incorporate this enhancement, too.

So what do you do about DoubleSpace? If you're already using Stacker, there's little reason to switch, especially since it will cost you $10 if you use the conversion program. If you have DOS 6 and haven't installed a compression program yet, go ahead and install DoubleSpace, and reinstall a couple of those big applications you've had to knock off your hard disk in the last year.