Just when many people are asking why they need IBM Corp.'s Personal System-2 computers, along come two Texas companies - Tandy Corp. and Dell Computer Corp. - with the first PS/2-compatible machines, otherwise known as clones.

None of the clones is available yet, but the information their makers have released indicates they won't offer much more than IBM's own PS/2 machines. And so far, there is no significant price advantage.There are also some questions whether most computer users want PS/2 technology and, even if they do, whether the clones can provide it as well as IBM.

Computer cloning - or the creation of machines that can run the same programs as the originals - became a widespread practice after IBM introduced its Personal Computer in 1981.

Compaq Computer Corp. of Houston, for instance, has been mining gold ever since it introduced one of the first IBM Personal Computer clones in 1982.

Other computer companies - including Tandy of Fort Worth, Texas, and Austin, Texas-based Dell - also entered the PC clone market. Together,they have sold millions of computers.

When Compaq and others introduced the first PC clones, there was a large demand for them. IBM's computers were in short supply, and clone companies offered more features at a lower price.

Because so many companies were selling IBM-like computers, IBM itself sold fewer of its own PCs than it wanted.

Last year, in response to this flood of PC clones from other companies, IBM changed the way it builds its personal computers. It discontinued its Personal Computer line - which included the original PC, the PC XT and the PC AT - and it introduced the Personal System/2 line.

Most of the PS/2s have a better graphics system (the Video Graphics Array) than the old PC standard, and they use 3.5-inch floppy disks that hold more information than the old-style 5.25-inch floppy disks.

The three most expensive PS/2 machines - Models 50, 60 and 80 - also include a new internal structure called the Micro Channel Architecture, or MCA, which is designed to let them use hard disks and networks more efficiently.

The only part of a PS/2 that can't be added to an old-style PC or PC clone is the MCA. MCA is an improvement to the computer bus, which is the electronic highway upon which computer data travels. Because the MCA bus works faster, the entire computer can work faster.

IBM has suggested that MCA will be even more useful in the future but

hasn't explained exactly how.

Buying a PS/2 for MCA is like buying the foundation and hoping the house will come later, said Bruce Stephen, senior personal computer analyst at International Data Corp. of Framingham, Mass.

When it announced the PS/2 line, IBM hinted it would sue any company that cloned the PS/2 for copyright infringement. But days before the Tandy and Dell announcements, IBM opened the door to clone makers, announcing it would sell other computer firms a license to produce PS/2 clones with the MCA.

With legal obstacles out of the way, Tandy said it would sell its 5000 MC in July. The Tandy PS/2 clone is compatible with the IBM Model 80, based on the Intel 80386 chip.

Two days earlier, Dell had announced it was working on two PS/2 clones called the System 400 and System 500 to be available at the end of the year. Dell's Model 400 will be compatible with the IBM Model 60, based on the Intel 80286 chip, and the Model 400 will be compatible with the Model 80.

Kaypro Corp. and Compaq are also rumored to be working on PS/2 clones.