We produced some real magic last month. We turned an old computer into a sleek teenybopper.

Our genuine IBM XT still ran as fast as the day we bought it in 1984. But compared to the 1987 AST Premium/286 and 1988 hotrod Compaq 386/20 gracing other desks, it was slllooooww.So we made some organ transplants. It was like giving Old Betsy a dip in the Fountain of Youth.

Our first transplant was to replace the hard disk drive. The original IBM XT 10 M drive averaged 90 milliseconds (ms) to find a piece of data. The $1,000 Priam 40 M add-on hard disk we installed cut the time to 28 ms. We now have over three times faster access to data and quadruple the storage space.

Priam makes add-on hard disk drives in many sizes, for Apple IIs and Macs as well as IBM types. We store our office files in a Priam that holds over 130 M.

You can tackle a disk replacement if you've put circuit boards in your computer. Quality makers of easy-add-on disks (such as Priam, Tallgrass, Rodime, Seagate, and Miniscribe) include manuals and software in their disk kits that make the job nearly foolproof for experienced tinkerers. They also offer telephone support.

Next we replaced Betsy's old, slow main processor chip. We couldn't just pull it out and stick in a fast new 80386 model. The new chip wouldn't fit.

Besides, to get up to speed, it needed new circuits. The answer was to install a circuit board containing the new chip and new circuits.

Old Betsy's Geritol treatment was a Quadram Quad386XT board. Like most of its kind, it also came with extra high-speed memory chips. We pulled out the old processor chip, plugged the new board's special cord into the vacant socket, and set the board in place.

Installing it and its new software took under an hour. It's simple for anyone who can open a computer case and take the time to read instructions.

We ran some before-and-after speed tests on this board. First, a word processor, we forced the computer to search a long file for a word. What took 102 seconds on the old XT, took 42 seconds after the Quad386XT board was in place.

Next we tested numbers handling. Our spreadsheet was so complex, the old XT took 542 seconds to recalculate after we altered one number. With the same spreadsheet but the new board, Old Betsy raced through in 42 seconds.

The board we used costs a hefty $1,200. But the speed increment could justify the price if you do a lot of numbers work. Most add-on speed enhancement boards also triple the amount of internal memory - RAM, in jargon - your programs have available to work with.

Our old XT had been delivered with only 256 K RAM, and we'd boosted that by adding Intel's AboveBoard memory expansion board. It gave us 2 M of RAM for many programs to make good use of - but not all, since programs written for older PCs and compatibles did not all use one of at least three available methods for calling on extra memory.

Newer computers like the 386s are much more adept memory handlers, so there's little incentive for software developers to write for klugy old PCs. We generally recommend against adding more than 640 K of memory to an old PC, XT, or older IBM compatible unless you also replace the old processor chip with an 80386.

You can ignore our warning if you use a program like Microsoft Word (END or Lotus 1-2-3, which are written so they can call on more than 640 K of RAM memory. If you don't think you'd benefit by adding extra processing speed, sure, add as much memory as you can afford.

We've tested and found reliable memory expansion boards from Quadram, Intel, AST, and STB. These days memory chips are scarce as hens' teeth, so be sure you know how much memory you're comparison-shopping. Many ads tell only how much memory a board can hold, not how much memory you're being sold!

Our old XT's next shot in the arm was to its graphics card. The original graphics board created the fuzzy old IBM PC standard character display on a monochrome monitor. Today's programs work best with today's much sharper viewing screens.

There are more ways of sending data to a screen than anyone needs to keep track of. The most common are CGA, EGA, VGA, MDA, and Hercules. We swapped our IBM's old card for a QuadRam EGA board. It can sense what display `standard' a particular program handles and set itself accordingly. We've tested and can recommend cards by AST, Genoa, and STB, too.

Next we replaced Old Betsy's monitor, unplugging its power cord and connection to the computer and plugging in the new. Inevitably, circuits installed before 1988 also need some switches reset. That involved reading the manual and doing extensive trial-and-error switch flipping.

When we want monochrome, we fasten an AST high resolution monitor onto the Quadram card. For color, we use a multi-synch type monitor by Thompson. Its picture is so sharp, it makes our TV look outmoded. In fact, when it's home, we wire it to our VCR and put an NEC multi-synch color monitor on our rejuvenated XT. It's not as great for TV viewing, but it's a joy for computer use.

Our last makeover step was to junk the old IBM PC keyboard in favor of a bigger, key-packed KeyTronic model. The firm makes so many, there's a layout to fit almost any taste. In all, the keyboard, boards, and color monitor added up to $3,700 worth of parts at retail prices. But performance now approximates a $7,000 machine like the Compaq Deskpro 386-20 or AST Premium 386.

Watch for our upcoming columns dealing just with computer graphics.

As a service to readers, the columnists answer questions and send a checklist of back issues if you enclose a stamped self-addressed envelope. A special 7,500-word report, `Buying Guide to Personal Computers,' reviews hardware requirements and brand names recommended by Peterson and K-Turkel. For your copy send a $3.50 check and stamped self-addressed envelope for Report FP14 to TBC, 4343 W Beltline Hwy, Madison WI 53711. Copyright 1988 P/K Associates, Inc.