Twice the effective RAM at a fraction of the cost - that's the promise of this new utility for the Mac. Does it deliver? Ian Waugh plays double or quits.

Even the name 'RAM Doubler' has got to make it one of the most tempting purchases ever. Double your RAM, Mister? You bet!

Of course there's a catch - or at least a few caveats - but the program does actually have the effect of doing what it says it will. I have chosen my words carefully - read on...

You can't physically double your RAM without adding more RAM chips. You can make your Mac think it has more RAM by switching on Virtual Memory which uses the hard disk as a storage area. RAM Doubler does neither of these. It basically uses your RAM more efficiently. When you load a few applications, each one reserves a portion of memory for itself - even though it may not all be used. Your word processor, for example, may reserve 2Mb when it loads, but if you're only typing a short note, most of the reserved RAM will be unused.

Constant loading and quitting of applications can result in fragmented memory, much like a hard disk becomes fragmented by constant saving and deletion of files. RAM Doubler optimises the RAM which is not being used so you can load additional applications. It may also occasionally use your hard disk - although this is most common if you have less than 8Mb of RAM.

RAM Doubler will not work with the Mac's Virtual Memory, although it is fully 32-bit compatible. Some older programs may not be 32-bit clean which could give rise to system errors or crashes. If you rely on one which causes a problem you can probably get an upgrade from the supplier. The Shareware program Check 32 will test programs for 32-bit compatibility.

The Mac's RAM Disk is allocated by the computer and so is not available for doubling. There are a few hardware devices which Doubler is not compatible with, too, such as some accelerators and special hard drive configurations. If you've got something weird contact your supplier or Computers Unlimited before buying the program. RAM Doubler works with all Macs which use a 68030 or 68040 chip. You must have at least 4Mb of RAM to start with and if you have less than 8Mb then you also need a hard disk (though there can't be many Mac owners without a hard disk these days!).

Because RAM Doubler is, obviously, doing a few calculations behind the scenes you may notice a very slight drop in performance on slower Macs. I must confess I didn't have any speed problems, but then I was using a Quadra. Generally, however, I'd suggest that the benefits outweigh the occasional time lag.

Because of the way that RAM Doubler works, if you only ever run one program at a time it may not give you much of an advantage. If you want to edit single, large sample files, you'll still get an Out Of Memory error. RAM Doubler is most useful for people who want to have several applications open at once. If you would like use your sequencer while still having instant access to three, four or more other applications but don't have enough RAM to load them all. Doubler is for you.

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