Computer equivalent of patting your head while rubbing your stomach

Personal computers are gaining an ability that is the electronic equivalent of patting your head and rubbing your stomach at the same time - the power to allow their users to do several things simultaneously.

The key to this new capability is an approach called windowing. This enables the operator to split the screen into a number of smaller ''windows'' on different software programs.

Thus, one window might contain a letter being written on a word processor, while a second might display names and addresses from a filing program. The operator can search for a specific name and address in the filing program. Then, with relatively few keystrokes, he or she can move the information into the letter.

In the past, personal computers have been limited to one application at a time. In addition, the number of steps involved in passing information from one program to another has generally been so great that it has been worthwhile only when large amounts of information must be transferred.

The real advantage of this approach is explained by Therese Myers, president of Quarterdeck, a software company marketing a windowing program. It allows people to customize their computer system ''to fit the way they work, rather than being forced to follow rigid guidelines.''

Windowing can make operating a computer somewhat simpler. But it is not without cost. Generally, these programs require a large amount of expensive computer memory (a half megabyte) and a costly hard disk for storage. This limits their use to computers that cost $5,000 or more.

The basic concept of windowing first made its appearance in single programs, like word processing. Splitting the screen into two or more windows enabled the writer to look at several parts of one document or several documents at once.

But it was Apple Computer's precedent-setting Lisa that first employed the concept to integrate the various tasks a computer is commonly used for. This had a great impact on the computer industry, which recognized the need to streamline the transfer of information between different applications.

The underlying concept, or metaphor, of Lisa is an electronic desk with a built-in filing cabinet and trash can. Different electronic files are opened and placed on the screen, much the way Manila files or pieces of paper are placed on a real desk. As on an actual desk, it is possible on the computer to lay one file on top of another. In fact, a person can totally ''bury'' one electronic ''folder'' under several others.

Shortly after Lisa was introduced, VisiCorp announced that it was developing a program called Visi On, which gives the IBM Personal Computer (PC) a capability similar to that of Lisa. This was the opening shot in what one pundit has since dubbed the ''window wars.'' Since then, at least half a dozen companies have introduced their own windowing software.

Dr. Egil Juliussen, an industry analyst with Future Computing, quips that '' 1984 will be crucial in determining who will become the window master of the world.''

Visi On, which has just been released, employs the same electronic desk metaphor as Lisa. In fact, an IBM PC with Visi On appears to be comparable in both capability and in cost to the Lisa. Actually, Visi On is a family of application programs tied together with a windowing ''software environment.'' It includes a word-processing program, an electronic spreadsheet for financial planning, and a graphing program. A filing program will be released shortly.

This is a closed system. It runs only specially written programs. To write software that will work with Visi On, in fact, a software company must have a $ 20,000 minicomputer.

VisiCorp's arch rival in the window wars is Microsoft, the company whose operating system and BASIC programming language comes with the IBM PC. Last month Microsoft lined up a number of computermakers and fellow software companies behind a radically different approach to windowing.

Rather than a separate, and relatively expensive, package of programs costing 100 to $250), as an extension of its MS-DOS operating system, which is supplied with a large number of computers. Microsoft's major twist is not windowing per se but establishing a new standard for how personal computers paint images on their display screens.

Current operating systems control the way the various pieces of a computer communicate, particularly the way information is stored and retrieved in its disk drives. But current operating systems do not handle the way images are drawn on the computer's CRT (cathode ray tube). Virtually every type of machine does it differently. This forces software houses to rewrite large parts of their computer code for each computer model. But once a manufacturer has customized Microsoft's Windows for its computer, the machine should run all programs written for Windows without alteration.

''This standardization is much more important than the windowing,'' says Thomas Anderson, who is in charge of software development at Hewlett-Packard, one of the companies supporting Microsoft.

The Microsoft program is not yet fully written and is not scheduled for release until mid-1984. But a limited version was demonstrated at the recent COMDEX computer show here in Las Vegas. And this illustrated that the basic approach has several other unique characteristics.

''We use a neat desk rather than a messy desk as our basic metaphor,'' gibes William Gates, Microsoft's president. Instead of overlaying windows of various types on the screen, Microsoft uses an approach called tiling. This does not allow windows to overlap. Instead, when the user changes the size of one window, the computer automatically resizes the other windows so they fill the screen without lapovers. Besides neatness, Mr. Gates says, this makes more efficient use of the screen.

In addition, tiling is less complicated to do and so appears to be somewhat faster than Visi On.

In addition, Microsoft claims it will run on less expensive machines. But VisiCorp claimed the same thing until recently. Also, Microsoft has yet to effect the part of the program that handles the transfer of information between the various windows, the most difficult part of the job.

Like Visi On, programs must be rewritten to work with windows. But according to Microsoft, the job is much smaller than adapting a program for Visi On.

What about people who already have a substantial investment in software? If they also have or are willing to get the extra memory and the hard disk required , owners of the IBM PC or a compatible machine will be able to get windowing capability with a program called DESQ from Quarterdeck.

Available next month, DESQ is the most open of the windowing products. It runs most existing software without modification. It cannot run programs with graphics, so when it encounters such a program it turns over the whole screen to it.

Other than this, ''it runs almost every package we've tried,'' says Quarterdeck's Ms. Myers.

Also, moving information between programs can take a long time - several seconds or more. But slowness is not a problem confined to this program. ''You may have noticed, one problem with a number of these programs is that they are not very fast,'' comments Esther Dysan of Rosen Research.

''One thing I really enjoyed, coming from mainframe computers to micros, was the simplicity of doing one thing at a time. But this won't last much longer,'' sighs one computer veteran.