Does your computer have enough memory? Probably not. Nearly every new development in computing will require your computer to have more random access memory (RAM).

Since 1987 memory prices have dropped from more than $400 to less than $100 per megabyte. All Macintoshes can easily accept and use four or eight megabytes of memory. Although IBM PCs were stymied for years by MS-DOS with its 640-kilobyte RAM limit, Microsoft Windows 3.0, introduced earlier this year, finally allows programs to make effective use of more memory. Most current IBM PCs and compatibles can be upgraded to accept at least four megabytes of memory.

Memory prices are still high for two types of computers. Battery-operated portable computers need high-priced, low-power memory. And some 386-based desktop models require memory that still costs $200 to $300 per megabyte. If you have such a desktop computer, you might want to consider either getting a newer design or changing the main computer circuit board so you can install standard cheap memory.

Where can you buy it?

* Mail order is the cheapest, at $50 to $60 a megabyte. Check the back pages of computer magazines. You'll have to install the memory yourself.

* Individuals who sell computer components will often do on-site installation and typically charge $70 to $90 a megabyte. You're best off finding such people through referrals; try a local computer-user group or a university computing center.

* Computer stores vary greatly in their memory pricing -- typically charging $100 or more a megabyte. On-site installation can add $50 to $100. Since the memory chips are standard, pricing has little to do with quality, so shop for the lowest price at the level of service you need. -- Cary Lu

* * *