In Plain English

CD-ROM player: A device that allows computers to run optical disks, known as CD-ROMs. These are highly prized right now because a single disk can hold 650 MB of data, the equivalent of 464 floppy disks. Software companies, especially game makers, cram sound and even video onto these disks to make their programs more appealing.

Floppy disks: They used to be flexible and floppy, but these portable storage disks now come in 3-1/2-inch squares of hard plastic. You can copy files from your computer onto a floppy disk, then take the floppy along to use in another computer or as a backup in case something happens to the original computer file.

Hard drive (also known as a hard disk): This is the spinning magnetic disk inside the PC that stores all the software and data you use or create. Its capacity to hold data is measured in megabytes.

Megabyte (often abbreviated MB in computer ads): 1 million bytes. One byte equals one letter of the alphabet, once. So 1 MB equals 1 million letters or about 167,000 words; 1,000 MB equals one gigabyte, which could hold the text of the world's largest modern encyclopedia (which has more than 100 volumes). Sound and pictures require much more space than words.

Microprocessor: the computer's main chip, which does most of the computing.

Display: the computer screen. On desktop models, it's called a monitor.

Modem: the device that allows a computer to send and receive signals over a telephone line.

RAM (random-access memory): the temporary storehouse for the data in use by a computer. It's also measured in megabytes, but has far less capacity than the hard drive. So next time you see an ad for ''486DX 540MB 8MB,'' you will be able to decipher that it's a 486-class IBM-compatible with a 540-megabyte hard drive and eight megabytes of RAM. (You know it's IBM-compatible because Macs don't use 486 chips; DX is a kind of 486 chip.)