NEC POWERMATE ES 5200 - SERVICE, Service Manual

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Glossary 9
H
hertz
(Hz) A unit of frequency equal to one cycle per second.
hexadecimal
A number system that uses 16 as the base. (Place value indicates powers of 16.) It
uses the digits 0-9 and A-F. Used around computers because a byte (eight binary
digits) easily converts to a two digit hexadecimal number. Hexadecimal numbers
are often indicated with the letter H, a dollar sign, or a subscripted 16 after the
number. Compare binary, decimal.
host adapter
An expansion board that serves as a controller for SCSI devices.
hot key
Combination of two or three keys (such as Ctrl-Alt-D ) that you press
simultaneously for a particular function.
hot plugging
The ability to add and remove devices to a computer while the computer is running
and have the operating system automatically recognize the change. The Universal
Serial Bus (see USB ) external bus standard supports hot plugging. This is also a
feature of PCMCIA. Hot plugging is also called hot swapping.
I
IDE
Intelligent Drive Electronics. A hard drive type that has controller electronics built
into the drive and delivers high throughput.
interface
A connection that enables two devices to communicate.
interrupt
A signal from part of a system, such as an I/O device, asking to use the CPU.
Interrupts are hierarchical, which prevents interrupts from interrupting each other.
(Whichever interrupt has higher priority makes the other interrupt wait.) When the
CPU receives an interrupt signal, it saves what it is doing, processes the routine
associated with the interrupt, then returns to what it was doing.
I/O address
Input-Output address. How the CPU sees an I/O port. It puts data into this address
or reads the data in it. The device at the other end of the I/O port gets the data from
that address or puts the data there, respectively.