(FORTUNE Magazine) – You've just finished renegotiating a complicated international merger, and now you're on the way home to report to the management committee. You're sitting in the cabin of the corporate Gulfstream III, 40,000 feet up over the Pacific, revising all the figures on the deal. You're punching the numbers into a GRiD 1530 portable computer that is only 11 1/2 inches wide by 15 inches long, with a glowing orange-on-black screen. The whole thing folds up into a black magnesium case less than 2 1/2 inches thick, small enough to toss in your briefcase. The machine looks faintly sinister, like something Darth Vader might have brought aboard the Death Star. It has a top-of-the-line microprocessor -- an Intel 80386, just coming into use in laptops -- and loads of memory in its 40-megabyte hard disk. The computer weighs 12 pounds and runs for one to three hours on a single rechargeable battery pack. Fully loaded, the machine can cost close to $8,000. Anybody in the market for a portable has four variables to consider: the power of the central processor, which determines how fast and versatile the computer is; the size and weight of the machine; whether it runs on batteries; and the type of screen. Cost, of course, is a factor too. In general, the smaller and more powerful the machine, the higher the price. Computing power is the central issue. The new GRiD machine is the most advanced portable available for the so-called power user who needs lots of number-crunching and graphics capability. Close behind -- for the traveling manager, auditor, or field engineer who wants to run spreadsheets and display graphics -- is the new Toshiba T5100, a 15-pound machine that does not run on batteries and won't quite fit into a briefcase. Cost: $6,499. GRiD and Toshiba are the first laptop makers to offer gas-plasma screens that handle graphics as well as high-grade office monitors. With 40-megabyte hard disks, their machines have as much storage as a desktop PC. Toshiba was the first manufacturer to market a range of laptop machines; GRiD and Zenith now do so as well. Toshiba pioneered the use of Intel's 80286 microprocessor -- the forerunner of the 80386 -- which lets portable computers do most of what machines with the newer chip do, but only about two-thirds as fast. The Toshiba T3100/20, which weighs 15 pounds, comes with a 20-megabyte hard disk for about $3,300. In this class, for $5,500, Toshiba also sells the bulkier, 19-pound T3200, with a full-size keyboard, a separate keypad for entering numbers, and expansion slots for plugging into a local area network at the office, for example. It will go head to head with a similarly equipped NEC PowerMate Portable at $2,880. Compaq's boxy ''luggables'' won't fit on anybody's lap, but they provide two important features of desktop computers -- a full-size keyboard and a superfast, shock-mounted, 5 1/4-inch disk drive. The 80286-powered Compaq III (about $4,000) and the new Compaq 386 ($5,500), named after the 80386 chip, are ideal for a manager who wants the speed and versatility of a desktop in a machine he can take home or to a client's office. At 20 pounds, they're not for the heavily loaded traveler, though they'll fit under an airline seat in a pinch. Thinking about adopting the new IBM PS/2 series of personal computers? IBM characteristically will not comment on plans to introduce a PS/2 portable in the U.S., though widespread industry rumor has it that one is forthcoming as part of the PS/2 line. IBM Japan is selling the PS/5535, a bulky, 80286- powered, 18-pound laptop with a backlit black-on-white liquid crystal display (LCD) screen. LCD screens are easier to read in bright light than the gas- plasma variety, and they consume less power. But the LCD image is not as sharp. MISI Co., of Torrance, California, is offering the IBM machine to Japanese-language users in the U.S. for $10,000, including a 100% duty. It is not a PS/2 machine and lacks the speed and power of the higher-end models. Detailed rumors about an Apple Macintosh laptop reached the trade press in February, but the company remains mum. It has already licensed Dynamac Computer Products Inc., a company in Golden, Colorado, to take Macintoshes apart, put them back together in briefcase size with folding screens and 20- or 40-megabyte hard disks, and resell them for $5,000 and up. The mini-Macs weigh 18 pounds. Zenith is coming out shortly with a 80286-powered version of its best- selling Z-181 and Z-183 models. The latest Z-183 -- a 15-pound model with the slower 8088 processor, a backlit LCD screen, a high-speed modem, and a 20- megabyte hard disk -- retails for $2,500. In the crowded market of laptops that do basic word processing and math, it vies with other machines that use the same processor: the Toshiba T1100 Plus ($1,600), the GRiDLite Plus ($1,950), and the Data General One/2T ($1,700). A tough competitor in this range is the NEC Multispeed EL ($1,450), which manages to achieve processing speed close to that of an 80286-equipped machine in a relatively low-cost laptop. For executives on the run who need laptops mainly for note taking, writing letters or speeches, and simple computing, machines like the Datavue Spark and the Toshiba T1000 are available without modems or hard disks for under $900. In a pinch they can handle spreadsheets, though they do so slowly and awkwardly. They weigh less than ten pounds; the Toshiba, unlike the Spark, fits inside a briefcase. The bulky new Tandy 1400LT, a more versatile version of the popular $500 Tandy 102 notebook computer, is on the market for around $1,600. But as cheaper, battery-powered machines with 80286 microprocessors become the industry standard, low-end machines will doubtless find less of a market among businessmen than among students and others with more data than dollars.