(FORTUNE Magazine) – Computer stocks have been working overtime for investors lately. While the market has climbed 20% from the post-crash low of early December, shares of some hardware and software makers have shot up twice as much. But not all computer stocks have been supercharged. Those of companies that sell midsize and large computers, like Digital Equipment and IBM, have eked out meager, ephemeral gains. The real story has been in desktop machines. ''Because of powerful new semiconductors and software,'' says Rich Edwards, a senior analyst with Robertson Colman & Stephens, a San Francisco investment banking firm, ''customers see they can do just about anything on a personal computer or workstation.'' Unit sales of these machines raced ahead 25% to 30% last year, and Edwards expects 1988 to be another record breaker even if the economy sours: ''In a recession a customer might cancel a mainframe purchase, but would probably just scale back a PC order.'' The companies analysts like are not fire-sale cheap. Most sell for more than 20 times earnings in the latest four quarters, well above the P/E of Standard & Poor's 500-stock index. But analysts see earnings for many computer makers zipping up 25% or more this year, vs. a rise of 10% or so for the S&P 500. If memory chips were not in limited supply, these companies would be raking in even more profits.

At Sun Microsystems, the world's leading manufacturer of 32-bit workstations, revenues and earnings have doubled on average each year since 1983. Analysts see no end in sight to the explosive growth. Sun has helped make the highly flexible Unix operating system developed by AT&T, which has a big position in Sun, an industry standard. Even though the chip shortage may crimp Sun's growth this year, William Welty of San Francisco's Hambrecht & Quist investment banking firm thinks Sun will earn $1.63 for the year ending in June, up 47% from last year, and $2 in fiscal 1989. Although growth has been less steady at Apple Computer, it cashed in big during last year's low-end boom. Thanks to strong sales of Macintosh computers to the business market, earnings almost doubled in 1987. Melinda Reach, an analyst with Merrill Lynch, sees profits climbing 50% this fiscal year, to $2.50. Hewlett-Packard, known for its sophisticated scientific machines, gets 35% of its computer revenues from smaller systems and peripherals. Hewlett's Unix- based engineering workstations are big sellers, and the company dominates the laser printer business. Edmund Spelman of Oppenheimer & Co. calls the stock one of his favorites. ''Hewlett is well positioned and has the momentum,'' he says. ''I think it will earn $3.50 in fiscal 1988, up a dollar from last year.'' In the CAD/CAM and computer-aided engineering area, the trend also runs strongly to potent, downsized models. John Connolly, the top investment strategist at Dean Witter, recommends Intergraph, a leading manufacturer of workstations designed for these tasks. Connolly sees Intergraph earning $1.70 in 1988, up 38% from last year. Interleaf of Cambridge, Massachusetts, produces software for the burgeoning world of desktop publishing, including a new package for use on Apple's Macintosh II. Interleaf recently slipped into the black, so its P/E is still sky-high. But Welty of Hambrecht & Quist expects a steep earnings rise. And what company can connect this potpourri of computers and software? 3Com can. The company, which makes products that hook up PCs and workstations into what are known as local area networks, or LANs, recently doubled its size by merging with rival Bridge Communications. Paul Sherer of Robertson Colman sees the LAN business growing more than 30% annually for the next several years.

CHART: COMPANY REVENUES NET STOCK PRICE RECENT latest four INCOME RANGE PRICE quarters in millions last 12 months P/E in millions multiple*

Hewlett-Packard $8,542.0 $707.0 $39.25-$73.625 $64.00 23.2

Apple Computer $3,041.3 $280.4 $13.75-$59.75 $45.00 21.2

Sun Microsystems $755.9 $48.0 $22.00-$45.75 $32.75 24.4

Intergraph $641.1 $69.9 $17.00-$30.50 $27.50 22.4

3Com $197.5 $18.0 $12.375-$25.875 $22.50 34.6

Interleaf $52.1 $5.2 $10.50-$24.125 $19.50 59.0

*Multiple based on earnings in latest four quarters, exclusive of nonrecurring items.

CREDIT: NO CREDIT CAPTION: MORE POWER AT YOUR FINGERTIPS Profits are zooming at these companies that make powerful new desktop computers and software. The Sun Microsystems 3/110LC, in the center, is used by options traders at Greenwich Capital Markets of Greenwich, Connecticut. DESCRIPTION: See above.