The difference between genius and mere intelligence is storage. The quick-witted react fast, but the true genius can call upon memories, experiences, and knowledge to find real answers—the difference between pressing a button fast and having the insight to know which button to press.
Computers are no different. Without memory, a computer is nothing more than a switchboard. All its reactions would have to be hard-wired in. The machine could not read through programs or retain data. It would be stuck in a persistent vegetative state, kept alive by electricity but able to react only autonomously.
The technology for remembering did not originate with computers. Ever since people had thoughts they deemed worth preserving, they have used mechanical means for aiding their memories. When early humans first took charcoal and ochre to sketch on the walls of their ritual caves, they were making mechanical memories of hunts and ceremonies, of men, bison, and mastodons. Primitive, perhaps, but even with all our modern technologies, we have yet to make a record of ourselves that has lasted as long as cave drawings.
Perhaps inadvertently, those drawings have survived for the long term. But we, as thinking people, rely on another kind of memory—short term. When you're working on a problem, you have to hold a piece of it in your mind—say, the one to carry when you're adding a column of numbers or the telephone number you looked up and need to dial.
Computers have the same need for two kinds of memory—both long term and short term. Long-term storage holds the stuff you hope your computer never forgets—your operating system, your programs, your data, and the MP3 music you've acquired. Your computer also needs short-term memory while it works on your programs.
Unlike human beings, whose memory is not understood well enough to distinguish the different processes required for the long and short term, computers use widely different but well-understood technologies for their long- and short-term storage. This part of the book will examine how the two kinds of memory fit and work together. We'll also look at the individual technologies involved in short-term and long-term storage.