Microsoft's Windows 3.0, unveiled last Tuesday, may turn out to be the most significant development in the nine-year history of IBM and compatible personal computers. The new software, which works with the MS-DOS operating system, makes it possible for millions of those machines to use an attractive graphical interface similar to the one on the Apple Macintosh.

Windows 3.0, with a suggested list price of $149, is neither a program nor an operating system. It is an operating environment. As such, it governs the look of the screen, the way users interact with programs and even the way programs operate. It runs under the regular MS-DOS operating system on any IBM compatible with an Intel 286, 386 or 486 central processing unit (CPU). Machines must also have a hard disk, a graphic display and at least 1 megabyte of memory. Although Windows will work with regular MS-DOS programs, it works best when used with software designed especially for Windows.

Windows 3.0 has four main advantages over regular MS-DOS. First, all programs written for Windows have a similar look and feel. Once you learn to use one Windows program, you have a head start on all the others. Second, the graphical environment assures that programs gives you on paper what you see on the screen. Third, Windows, like the Mac, makes it easy to transfer data from one program to another. It's as simple as highlighting the information with the mouse, copying it to the clipboard and pasting it in another program.

Finally, Windows 3.0 is a multi-tasking operating environment. That means it's possible to load several programs into the computer's memory and switch between them with a single command or mouse movement. You can even have several programs share the screen, each in its own window.

Windows 3.0 can take advantage of as much as 16 megabytes of memory. Regular MS-DOS programs can use only 640K.

Users whose machines are equipped with an Intel 386 or 486 CPUs can to use Windows to run several DOS or Windows applications in the background, with each program behaving as if it's running in its own dedicated PC. It's also possible for 386 users to allocate part of their hard disk to simulate random access memory. This so-called virtual memory lets the 386 to continue to run programs after you've run out of regular memory.

You can't run Windows 3.0 on a PC or PC/XT equipped with an Intel 8088 or 8086 CPU. However, most of those machines can be modified with faster CPUs.

If you buy Windows you should also count on buying new Windows-compatible software. It's possible to use your old software, but the programs will look and operate just like they always have. They will not offer Windows's graphical user interface, although you will be able to use Windows to copy and paste information between regular DOS programs or between DOS and Windows programs.

Windows 3.0 comes with several free programs to get you started, including a basic word processing program, a calculator, a couple of games, a reasonably good communications program and a personal organizer, called Daybook.

Early versions of Windows were criticized as being slow and ugly. The new Windows is a lot faster and a lot prettier. I've been using a pre-release copy for about a month and I'm extremely impressed at its features, performance and reliability. I didn't get out my stopwatch to perform any timing tests, but its performance on my 386-based PC seems at least as good as what I'm getting on a similarly equipped Macintosh IIci, a machine that's more than twice the cost of my PC.

Microsoft and other software companies are rushing to provide software to run under Windows. Microsoft has already released Windows versions of its spreadsheet (Excel) and word processing (Word) software. Software Ventures has announced a forthcoming version of its Microphone Communications software. Some very good utilities programs for Windows, including one that makes it easier to locate and run programs, have also been released by hDC Computer Corp. of Redmond, Wash. Asymetrix of Bellevue, Wash., has already released ToolBook, a software development tool that is similar to Apple's HyperCard language.

The new version of Windows brings many advantages of the Apple Macintosh to lower-priced IBM compatibles. It breathes new life into the old MS-DOS operating system

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