Bit is a contraction of the words binary digit.

The 0's and 1's are called bits. They're not really 0's and 1's; they're opposite conditions, but it's more convenient to represent them as numbers. Even though it takes only seven bits to represent each character on the keyboard, the computer allocates eight bits for each character. The extra bit is sometimes used for error checking. A string of eight bits is called a byte.

The computer also uses 0's and 1's to do arithmetic. Whereas humans use a decimal numbering system (based on the number of fingers on their hands), computer use a binary numbering system (based on the two symbols they know how to manipulate: off/on or 0/1).

So, the computer processes information as 0's and 1's. It stores these 0's and 1's in RAM, which stands for random-access memory. It's called random-access memory because the microprocessor can go directly to any information it needs—it doesn't have to access the information sequentially the way you read a novel. The important thing to remember about RAM is that anything you store there is temporary. When you turn off the power, everything in RAM is erased—that's why you have to remember to store documents on disks.

Do not confuse RAM with a similar acronym, ROM. ROM, which stands for read-only memory, is the computer's permanent memory. It's called read-only memory because the microprocessor can read and use what's on ROM chips, but it can't store anything there. ROM chips contain the information that tells the computer what to do when you turn on the power, and other important indispensable information. That's all you need to know about ROM. RAM is of much more interest to you because that's where the computer keeps track of the application you're working with and the document you're working on. When this manual refers to memory, it's almost always referring to RAM.

Programs in ROM are called firmware.

Essential jargon

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