Specifications

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Appendix A Glossary
IRQ (interrupt request) Physical connections
between external hardware devices and the inter-
rupt controllers. When a device such as a floppy
controller or a printer needs the attention of the
CPU, an IRQ line is used to get the attention of
the system to perform a task. On PC and XT IBM-
compatible systems, eight IRQ lines are included,
numbered IRQ0–IRQ7. On the AT and PS/2 sys-
tems, 16 IRQ lines are numbered IRQ0–IRQ15. IRQ
lines must be used by only a single adapter in the
ISA bus systems, but devices on Micro Channel
Architecture (MCA), PCI (Peripheral Component
Interconnect) and PCI Express buses can share
interrupts. See also virtual IRQ.
ISA (Industry Standard Architecture) The
bus architecture introduced as an 8-bit bus with the
original IBM PC in 1981 and later expanded to 16
bits with the IBM PC/AT in 1984. ISA slots are occa-
sionally found in PC systems today, but the latest
chipsets have eliminated them.
ISA bus clock Clock that normally operates the
ISA bus at 8.33MHz.
iSCSI Short for Internet SCSI, this is an implemen-
tation of SCSI that uses Ethernet networks using
TCP/IP to transfer data in both directions between
a server and a SCSI drive or drive array.
ISDN (Integrated Services Digital Network)
An international telecommunications standard that
enables a communications channel to carry
digital data simultaneously with voice and video
information.
ISO (International Standards Organization)
The ISO, based in Paris, develops standards for
international and national data communications.
The U.S. representative to the ISO is the American
National Standards Institute (ANSI). See also High
Sierra format.
ISO 9660 An international standard that defines
file systems for CD-ROM discs, independent of the
operating system. ISO (International Standards
Organization) 9660 has two levels. Level one pro-
vides for DOS file system compatibility, whereas
level two allows filenames of up to 32 characters.
See also High Sierra format.
ISP (Internet service provider) A company
that provides Internet access to computer users.
Most ISPs originally provided dialup analog modem
service only, but many ISPs now provide various
types of broadband support for DSL, cable modem,
or fixed wireless Internet devices. Some ISPs, such
as America Online (AOL), also provide proprietary
content.
Itanium An Intel eighth-generation processor,
codenamed Merced, it is the first 64-bit instruction
PC processor from Intel. It features a new Explicitly
Parallel Instruction Computing (EPIC) architecture
for more performance when running optimized
code. Also, it features internal L1/L2 and L3 error
correcting code (ECC) caches to improve through-
put and reliability. It was designed initially for the
server or high-end workstation market. The
improved Itanium 2 processor offers faster clock
speeds and faster cache memory. See also L3 cache.
ITU (International Telecommunications
Union) Formerly called CCITT. An international
committee organized by the United Nations to set
international communications recommendations—
which frequently are adopted as standards—and to
develop interface, modem, and data network rec-
ommendations. The Bell 212A standard for
1,200bps communication in North America, for
example, is observed internationally as CCITT V.22.
ITU standards for telecommunications used in PC
based modems include V.22bis (2,400bps) through
V.92 (56Kbps).
J-lead J-shaped leads on chip carriers, which can
be surface-mounted on a PC board or plugged into
a socket that then is mounted on a PC board, usu-
ally on .050" centers.
jabber An error condition on an Ethernet-based
network in which a defective network card or out-
side interference is constantly sending data, pre-
venting the rest of the network from working.
Java An object-oriented programming language
and environment similar to C or C++. Java was
developed by Sun Microsystems and is used to
create network-based applications.
JavaScript A scripting language developed by
Netscape for web browsers. JavaScript can perform
calculations and mouse rollovers, but it doesn’t
require the web browser to download additional
files, as with Java.
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