IBM AT 5170 Technical Reference page 464

head. A device that reads, writes, or erases data on a storage
medium; for example, a small electromagnet used to read, write,
or erase data on a magnetic disk.
hertz
(Hz).
A unit of frequency equal to one cycle per second.
hex. Common abbreviation for hexadecimal.
hexadecimal. (1) Pertaining to a selection, choice, or condition
that has 16 possible different values or states. These values or
states are usually symbolized by the ten digits 0 through 9 and the
six letters A through
F. (2)
Pertaining to a fixed radix
numeration system having a radix of 16.
high impedance state. A state in which the output of a device is
effectively isolated from the circuit.
highlighting. In computer graphics, emphasizing a given display
group by changing its attributes relative to other display groups in
the same display field.
high-order position. The leftmost position in a string of
characters. See also most-significant digit.
hither plane. In computer graphics, a plane that is perpendicular
to the line joining the viewing reference point and the view point
and that lies between these two points. Any part of an object
between the hither plane and the view point is not seen. See also
yon plane.
housekeeping. Operations or routines that do not contribute
directly to the solution of the problem but do contribute directly
to the operation of the computer.
Hz. Hertz
image. A fully processed unit of operational data that is ready to
be transmitted to a remote unit; when loaded into control storage
~
in the remote unit, the image determines the operations of the
unit.
Glossary-18