MACINTOSH - STORAGE AND MEMORY

Washington University in St. Louis, School of Medicine

Storage vs. Memory

Many people are confused about the distinction between storage and memory. For example: why do you get out-of-memory messages when there's still plenty of room on your hard disk. Storage and memory are both ways of retaining information, and they are both measured in the same units, bytes, kilobytes, megabytes etc. The difference is how the information is retained. With memory the info is stored electronically on chips, and in storage it's saved on media, either magnetically on disks or tapes, or optically on disks or CD-ROMs. Memory is the same as RAM. RAM is the place where the computer temporarily keeps information you are working with. Information in the RAM can be accessed very quickly (compared to the hard disk) but is volatile. If you turn off your computer what was in the RAM vanishes. (File cabinet and desk analogy).

When you issue the Save command from within an application, the computer takes information from the RAM and puts it into storage media like hard disks and floppies.

Hard Disk (or Drive)

Hard Disk is where all the computer information including the system folder, programs and documents, is stored permanently (unless it crashes). Hard Disks store a lot more information than a floppy disk or the memory can store. The computer reads and writes from the Hard Disks much faster than the floppies. Hard Disk can be either internal or external. For more info on Hard Disks click here

Floppy Disks

Floppies disks come in 3 sizes:
400K, single-sided disks use only one side of the disk (like using one side of the blank piece of paper)
800K, double-sided disks use both sides of the disk (like using both sides of the blank piece of paper)
1.4MB , High_density disks use both sides and pack the information more tightly
For more info on Floppy Disks click here

CD-ROM drives

CD-ROMs (compact disk, read-only memory) are a particular kind of compact disk that uses optical technology to store information. Whereas the CD-ROMS can store upto 600MB (equivalent to seven hundred, 800k floppies and well over a quarter of a million type written pages) of information, they are very slow (by about a factor of 10) compared to Hard Drives.

Magneto Optical (MO) drives

Newer technology than CD-ROMs. The MO Drives are faster than the CD-Roms but slower than hard disks. They come in different sizes: 128MB
250MB
A few GB

The notes are based on The Macintosh Bible, 4th Edition, Arthur Naiman et. al., Peachpit Press, 1987-92.

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WWW Department of Molecular Microbiology, Box 8230 Washington University School of Medicine St. Louis, MO 63110-1093 USA	Tel 314-362-7059 FAX 314-362-1232 Last updated September 7, 1995.