The computer trade press is breathless over the long-awaited arrival of Microsoft's new operating software for the IBM PS/2 personal computer. OS/2, as it is called, will unlock the power of the newer processing chips.

Instead of a mere 640K of memory, OS/2 will address megabytes of RAM. Instead of one program at a time, OS/2 will be able to simultaneously run as many programs as your computer can hold in memory. Similar capabilities in the new Macintosh II have produced comparable excitement in the Apple world.

It might, therefore, surprise many readers that there is a personal computer that has been doing these things for two years.

This machine also can display as many as 4,096 colors at once (compared with the 256 colors available in the latest IBMs). Even more surprising is that you can buy this computer, with 512K of RAM and a color monitor, for less than $1,000.

The computer is the Commodore Amiga, easily the most technically dazzling personal computer on the market today and possibly the greatest value. It is certainly the most fun. Its video and sound make games on the Amiga the closest thing to having a video arcade at home.

There is, for example, Firepower, a tank-warfare game played against the computer or another player. You control a tank and pursue the enemy's flag, while dodging helicopters and artillery amid an almost deafening, and realistic, battle roar.

You can blast through walls, blow up gun emplacements and shoot down helicopters. The explosions are in vivid color and when you run over an enemy soldier, there is a gory splat.

The Amiga version of Silent Service, a popular submarine simulation available for a number of computers, also makes impressive use of the computer's graphics and sound. The warning horn signifying that the sub is about to dive is as real as anything you've heard in movies.

So are the sounds of the torpedoes and of deck guns firing. They should be. They were made by recording the real thing and digitizing it.

Gridiron, a football game, is nothing special graphically, just dots on a green field. The plays, both offensive and defensive, are simple, but realistic.

After weeks of testing, an 18-year-old computer football buff rated this game more entertaining than his other favorite, NFL Challenge for the IBM PC.

The games are similar: Choose a play and the computer chooses a defense (or offense, depending on which side has the ball).

But with Gridiron, unlike NFL Challenge, you do more than watch the outcome. You control one of the players after the action begins.

Flight Simulator, also available for a number of computers, shines on the Amiga, largely because of the realism of the sound, which is a digitized tape of plane engines.

If you have a modem, you can run Flight Simulator in tandem with another Amiga user. Once connections are made, you are able to see each other's planes.

Its graphics and sound have made the Amiga the personal computer of choice for certain specialized applications.

Music software for the Amiga ranges from simple programs children can play, with the computer keeping the tone deaf on key automatically, to sophisticated packages suitable for professional composition.

Draw-and-paint programs are spectacular and have helped the Amiga define a new application: desk-top video.

Not only can you create high-quality artwork and animation but, with the help of a video camera, you can also capture and modify color photographs. With additional equipment, you can manipulate the images on a videotape, then record and play back the modified version with your own sound track.

The Amiga uses a mouse and the point-and-click system that is familiar to Apple Macintosh users and is widely acclaimed for its ease of use. It can address up to 9.5 megabytes of RAM, and all you do to get several programs running at once is click the current task into the background and move the pointer to a new one; two more clicks of the mouse and it's going.

The Amiga comes in two sizes: the 500, which has one 3 1/2-inch, 800K floppy-disk drive and sells for $995 with a color display; and the 2000, which accommodates two internal 3 1/2-inch disk drives and has room for an internal hard disk. It also has space for a 5 1/4-inch floppy drive to be used with a special expansion board that is, in effect, an IBM-compatible computer unto itself. The 2000 sells for $2,000 and up.

Nothing has been said here about the Amiga's performance in such basic applications as word processing and data-base management. For all its power, they have not been the Amiga's strength, and the computer has had little impact in the lucrative business market.

Business software for the Amiga was originally scarce. But there is a lot of it now, and a "bridge board" permits software written for the IBM family to run on the Amiga 2000.

More about the bridge board and the Amiga as a business computer in my next column.

Brit Hume is a contributor to the Washington Post Writers Group. Hume is an ABC News Capitol Hill correspondent and the founding editor of a computer newsletter.