Hardware Reference
In-Depth Information
Graphics adapter
An option card which provides a specific graphics cap-
ability (e.g. CGA, EGA, HGA, and VGA). Graphics signal generation is not
normally part of the functionality provided within a system motherboard.
Handshake
An interlocked sequence of signals between peripheral devices
in which a device waits for an acknowledgement of the receipt of data before
sending new data.
Hard disk
A non-flexible disk used for the magnetic storage of data and
programs (see also
Fixed disk
).
Hardware
The physical components (e.g.
system board,
keyboard,
etc.)
which make up a microcomputer system.
High state
The more positive of the two voltage levels used to represent
binary logic states. A high state (logic 1) is generally represented by a voltage
in the range 2.0-5.0 V.
High memory
A legacy term used to describe the first 64 K of extended
memory. This area is used by some DOS applications and also by Windows.
See
Extended memory
.
IDE
IDE (or 'Integrated Drive Electronics') is the forerunner of the EIDE
interface used in most modern PC's. See
EIDE
.
Input/output (I/O)
Devices and lines used to transfer information to and
from external (peripheral) devices.
Integrated circuit
An electronic circuit fabricated on a single wafer (chip)
and packaged as a single component.
Interface
A shared boundary between two or more systems, or between two
or more elements within a system. In order to facilitate interconnection of
systems, various interface standards are adopted (e.g. RS-232 in the case of
asynchronous data communications).
Interleave
A system of numbering the sectors on a disk in a non-consecutive
fashion in order to optimize data access times.
Interrupt
A signal generated by a peripheral device when it wishes to gain the
attention of the CPU. The Intel 80
86 family of microprocessors support both
software and hardware interrupts. The former provide the means of invoking
BIOS and DOS services whilst the latter are generally managed by an interrupt
controller chip (e.g. 8259).
ISA
ISA (or 'Industry Standard Architecture') is the long-surviving standard
for connecting multiple interface adapters to the PC bus. Due to speed limita-
tions, the ISA bus is no longer used for hardware that requires fast data through-
put and local bus schemes (such as VL-bus or PCI-bus) are much preferred.
Isochronous data transfer
Data transfer (i.e. the movement of digital infor-
mation from one place to another) is said to be isochronous when the stream
of digital information does not require a separate clock or timing signal. In
effect, the timing of the isochronous data stream is implied by the rate at which
it is delivered. In the Universal Serial Bus, isochronous data transfers provide
periodic, continuous communication between a host and a device.
