Apple Lisa - Page 61

Confidential
Gate
Handshake
Hang
Hard disk
High
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lOB
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Low
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Mainframe
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Lisa Hardware Reference Manual
A
gate is a switch which controls the flow of data
according to some Boolean function of its inputs.
An AND gate, for instance, has two inputs, a data
line and a control line. If the control line is
o (false), data from the input line cannot get to
the output (anything AND false is false). If the
control line is 1 (true), any data on the data line
is allowed to pass through the gate.
Handshaking controls the transfer of data between
devices. Each device has a way to tell the other
that its side of the operation is complete. For
example,
a processor writes data to a register,
then sends a signal to a device that data is ready
to be read. The device reads the data, then sends
the processor a signal that it has finished reading
and is ready for more. The handshaking insures
that the processor does not write new data to the
register (clobbering the old data) before the
device has had a chance to read the old data.
A computer hangs when it gets into some infinite
loop or wait state. There are times when the only
recourse is to reboot the machine.
A disk that is not floppy. Hard disks look a little
like a stack of p'honorecords. Higher data densities
can be supported by a hard disk because it does not
change
size and position as much as the floppy disk
does.
A voltage state. A high voltage can signify either
true or false, depending on the logic being used.
Kilo-Hertz (1000 cycles per second)
Input/Output Block. A block of memory used to control
and communicate with the floppy disk controller.
7-Jul-81
Light Emitting Diode. A semiconductor device that emits
light when a small current passes through it.
A voltage state (0 volts). Low voltage can signify either
true or false, depending on the logic being used.
milliamp
The main computer.
Megahertz
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