One of the highly touted benefits of the new generation of personal computers is their ability, with the right software, to run more than one program at a time. But, as journalist James Fallows observes in a sensible article on new computers in the November Atlanticmagazine, most people don't need to do this. Many would like, though, to switch quickly from one program to another.

Happily, you don't need a state-of-the-art computer to do that, or even an expensive operating environment, such as Microsoft Windows or Quarterdeck's Desqview. What you do need is any IBM-compatible PC with a hard disk and some expanded memory -- 1 megabyte or more. With that, there is simple, inexpensive software that will let you shift quickly from one program to another.

The most tried and true of such programs is Software Carousel, $89.95 from SoftLogic Solutions. In simple terms, it works this way: Your computer's memory is treated as a vast block of working space. It is broken into as many as 12 partitions, with each assigned an amount of memory you choose.

Once the program is running, you may switch from one partition to another at the touch of a "hot key." Each partition functions like a separate computer. So you can load your word processor into one, your database into another and so on.

When you switch partitions, the contents of one are swapped out of main memory into expanded memory. That makes room in active memory for the program in the next partition. The process is almost instantaneous on AT-class or faster computers, but it can take a few seconds on XT-class machines.

An example of Software Carousel's usefulness was a review last April of PC-Globe and PC-USA, two computer atlases that put maps and extensive geographic information at your fingertips. The programs are large and cannot normally be used while running other programs. Software Carousel, however, kept both programs just a keystroke away in two separate partitions while the review was written in a third.

An interesting newer entry in the task-switching category is Back & Forth, $69.95 by mail from Progressive Solutions, 1321 Klondike, San Antonio, Texas 78250 (512-670-1061). You can also try it free as shareware, which is software that is available on computer bulletin boards and paid for on an honor system. Back & Forth functions much like Software Carousel, except that it allocates memory either by program or by partition.

Back & Forth also permits programs to be loaded automatically when you start it and lets you cut and paste data between programs, something Software Carousel can't do. It also includes a phone dialer. This is not a full-blown modem-communications program, however, and the instructions warn that Back & Forth cannot swap a communications program in and out of memory while your modem is on-line with another computer.

This did not happen when I tried it. But when a vendor says a program won't do something, it can't be counted on to do it. So beware. One more thing: The shareware version of Back & Forth is a full-working copy, but it includes an opening message that stays on your screen for 30 seconds before the program starts. It's supposed to be an incentive to pay for a registered copy, but some may find it an incentive to try something else.

You can get the shareware edition from the CompuServe on-line service or from the Public Software Library, P.O. Box 35705, Houston, Texas 77235-5705 (713-665-7017). Also available is an older, obscure program called DOSamatic. It hasn't been updated since 1986 and uses neither expanded memory nor disk space for swapping.

DOSamatic, instead, performs the simple function of letting you load more than one program at a time into main memory and toggle between them.

DOSamatic is useful, for example, in keeping a word processor and modem-communications program going at the same time. This is a timesaver for the traveler who needs to stay on-line with an office system while being able to write messages and memos for transmission to the office.

DOSamatic is also a file manager similar in appearance to Xtree, but with far fewer features. It permits the viewing, copying, deleting, printing and renaming of individual files, but not marked groups of files. The file manager remains in memory and available at all times when you are using DOSamatic.

DOSamatic's main virtue is that it works on any system and is fast even on the slowest computer. Note: The company that developed DOSamatic may no longer be in business, so don't send any registration fees for the program until you determine if there is anyone to receive the money.

Brit Hume is a contributor to the Washington Post Writers Group. He is chief ABC News White House correspondent and the founding editor of a computer newsletter.