Apple Lisa - Glossary

Confidential
Lisa Hardware Reference Manual 7-Jul-81
GLOSSARY
Asynchronous modem
Autovector
Baud rate
Bit
Block
Boot
Bus
Byte
Byte
parity
Card cage
Checksum
A
modem which handles asynchronous transmissions.
In asynchronous communication each character is
transmitted with its own framing information telling
the receiver where the character starts and stops.
Since each character is a complete message, the time
interval between successive characters need not be
fixed.
To handle certain interrupts, the 68000 automatically
jumps to a location predefined for the given interrupt.
The jump to the interrupt handler preloaded at this
location is called an autovector.
The rate at which a Modem sends and/or receives
information. 110 baud means the Modem is handling
approximately 110 bits per second. If there are
two stop bits, a start bit, a parity bit, and a
seven bit ASCII character code, 110 bits per second
translates into about 10 characters per second.
An acronym for binary digit. A bit is a piece of
data with only two possible states, 1 or O.
A contiguous set of bits.
When a computer is turned on, it has to I~ootstrapn
itself into a useable state. The process of getting
the operating system software into place and executing
is called booting.
A set of parallel wires (traces, paths) which carry
related data and control information from one device
to another.
A group of bits. On the Lisa, a byte is always 8 bits.
When bytes of data are being moved around, one or more
bits in the byte can get improperly flipped. These
incorrect bits can sometimes be detected by checking
the byte parity. The byte's parity is odd if there is
an odd number of 1 bits in the byte. If another bit is
available in the byte, the sender can insure that every
byte has even parity upon being transmitted. The receiver
can then check each byte's parity, and if any are odd,
it can inform the system that something has gone wrong.
The
metal box in which the printed circuit cards reside.
Similar to byte parity. A number used to ensure that
data has not suffered degradation during transfer.
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