As time goes on it becomes increasingly likely that you'll need to transfer the programs and data you have stored in one computer to another.

Several factors make it so. New-generation computers with 386 chips offer major improvements in performance at bargain prices, tempting many owners of older IBM-compatible machines to buy new models.

Furthermore, many users have added portable computers to their equipment, usually as a supplement to a desktop unit.

There are a couple handy ways to accomplish such transfers.

One is the use of special file transfer software in which two computers are connected by cable. Of the several good products to do that job, I have recently tested Fastlynx, from Rupp Corp. of Los Angeles.

Another newer and more powerful way to do it is with a portable hard disk that can be connected to first one and then another computer. I have tested the DataFile unit from Axonix Corp. of Salt Lake City, which comes in several sizes ranging from 20 to 200 megabytes of storage priced from $799 to $2,299.

Fastlynx, which has a reputation for being the fastest of the file transfer programs, comes in a $150 (suggested retail price) package that contains two special transfer cables along with software on both 3.5- and 5.25-inch diskettes.

One of the bright red eight-foot cables is designed to connect a pair of computers by their serial ports. Each end of the cable has two connectors, one for 25-pin serial ports and the other for 9-pin ports.

The other cable connects the computers through their parallel ports -- the port normally used for connecting to a printer.

There are a couple of ways to use Fastlynx, including expert modes that let you issue streamlined commands. But the easiest way, especially for occasional use, is the "split-screen" mode in which the names of the files on each computer are displayed in side-by-side lists. You choose which files to copy to which computer by highlighting their names using the keyboard.

You have to be careful that the list for the receiving computer is positioned on the directory in which you want the new files to be placed, however. It is easy to copy files into the wrong place, which I proved to myself more than once.

Additional software is included with Fastlynx that lets you connect two computers together more or less permanently. Then the second computer has access to all of the programs, data files and even the printer on the first computer. It isn't a substitute for true networking, but it might make sense in a two-person office.

Using the standard cables supplied with the program, the computers would have to be within several feet of each other. But special cables are available from Rupp that would let them be as much as 100 feet apart.

The idea behind the Axonix portable hard disk is basically the opposite of file transfer. It allows you to keep your files in one place -- on the portable disk -- and move the disk around among two or more computers.

Called the "DataFile," the portable hard disk measures roughly three inches high, six inches wide and eight inches deep. There is also a separate power transformer box with input and output electrical cables to contend with. Even so, the combined weight is less than four pounds and it is small enough to be carried in a small tote bag or an attache case.

The DataFile hard disk connects to any computer through its parallel printer port. If your computer has two such ports, it will automatically assume that it is connected to the second, preventing interference with the printer connected to the first port. (Your computer will know the ports by the names LPT1 and LPT2. Most computers, however, have only LPT1.)

The DataFile opens a lot of possibilities. If you were going on a trip where there would be IBM-compatible computers available at your various stops, you could take the DataFile and have the twin advantages at each stop of working on your own files with your own software and using a desktop computer, which is usually more pleasant to use than a portable.

Similarly, you could take your work back and forth from office to home on the DataFile. At home you could get by with a very inexpensive single floppy drive computer -- desktop or portable -- because the DataFile would serve as the hard disk.

Considering that the DataFile costs about the same as a good tape backup unit of similar capacity, it could serve double duty as both your backup system and your data transport system.Richard O'Reilly designs microcomputer applications for the Los Angeles Times. Readers' comments are welcomed, but the author cannot respond individually to letters. Write to Richard O'Reilly, Los Angeles Times, Times Mirror Square, Los Angeles, Calif. 90053.