Classic Computer Magazine Archive COMPUTE! ISSUE 39 / AUGUST 1983 / PAGE 72

Questions Beginners Ask

Tom R. Halfhill, Features Editor

Are you thinking about buying a computer for the first time, but don't know anything about computers? Or maybe you just purchased a computer and are still a bit baffled. Each month in this column, COMPUTE! will tackle some questions commonly asked by beginners.

Q I keep seeing printers and computers advertised with features such as "full ASCII character set" or "ASCII keyboard," etc. What does ASCII mean?

A ASCII stands for "American Standard Code for Information Interchange." Basically, it's a way of encoding characters (letters, numbers, punctuation, special symbols) into standardized numbers that can be understood by any computer or computer device. ASCII was invented to allow all types of computers, terminals, keyboards, printers, modems, disk drives, and other peripherals to easily communicate with each other. It's like the "Morse code" for computing.

The "ASCII character set" is a table of all the letters, numbers, punctuation marks, and other symbols that any computing device might need to communicate with another. Each character in the ASCII table is represented by a number ranging from 0 to 127. For instance, the ASCII code number for the letter "A" is 65; the code for the number "0" is 48; the code for an exclamation mark ("!") is 33. (Many computer manuals and books have an appendix with a table of the ASCII codes.)

When a computer sends something to be printed on a printer, for example, the characters are converted to ASCII numbers by the computer, transmitted along the printer cable, and then recognized by the printer as the original characters. Thus, when a printer is advertised as having a "full ASCII character set," it means the printer is capable of recognizing and printing any standard ASCII character.

Likewise, a "standard ASCII keyboard" means that the computer or terminal keyboard can type any ASCII character. This is especially important for computers or terminals that will be used for telecomputing (hooking up to distant computers over telephone lines). Some of the ASCII codes are "control codes" — they transmit a command encoded as a character. For example, the ASCII code "7" stands for "bell." It rings a built-in bell or buzzer found on most computers and terminals. ASCII code "13" means "carriage return" and is like pressing the RETURN or ENTER key on the keyboard.

The subject of character codes can become very complicated, because even computers which have ASCII keyboards and which communicate with outside devices in ASCII do not necessarily use ASCII internally.

Atari computers, for example, use ASCII for letters and punctuation, but deviate from ASCII for the control codes — such as 155 for carriage return (versus 13 in true ASCII) and 253 for the bell, as opposed to ASCII's 7.

Commodore computers send control characters as ASCII, but the codes for the lowercase alphabet (normally 97-112) are offset by 64. This can cause problems when you try to hook up a standard ASCII printer (usually upper- and lowercase come out reversed).

Apple computers use true ASCII and can even send lowercase, although you can't display lowercase on an unmodified Apple II. Both the Texas Instruments TI-99/4A and the TRS-80 Color Computer use true ASCII.

Any computer can be made to send and receive true ASCII with a hardware or software interface. That's one of the functions of "terminal software" in telecomputing: a special program translates the computer's output to universal ASCII.

Q What exactly is a "port," as in "user port," or "serial port," or "input/output port"?

A A "port" is simply a slot or a jack on a computer where external devices may be plugged in. It's similar to the jacks on a stereo receiver which allow you to add on speakers, tape decks, turntables, and other accessories.

There are many different types of ports, and often they are incompatible among different computers. That's one reason why you can't plug an Apple disk drive directly into a Commodore 64, or an Atari cassette recorder into a VIC-20.