Fujitsu T4310 Guide D'utilisation page 148

Within an isolated network, you can assign IP addresses at random as long as each one is unique.
However, connecting a private network to the Internet requires using registered IP addresses (called
Internet addresses) to avoid duplicates.
The four numbers in an IP address are used in different ways to identify a particular network and a
host on that network. Three regional Internet registries -- ARIN, RIPE NCC and APNIC -- assign
Internet addresses from the following three classes.
Class A - supports 16 million hosts on each of 126 networks
Class B - supports 65,000 hosts on each of 16,000 networks
Class C - supports 254 hosts on each of 2 million networks
The number of unassigned Internet addresses is running out, so a new classless scheme called CIDR
is gradually replacing the system based on classes A, B, and C and is tied to adoption of IPv6.
IR
An abbreviation for infrared.
IrDA
Infrared Data Association. An organization which produces standards for communication using
infrared as the carrier.
IRQ
Interrupt Request. An acronym for the hardware signal to the CPU that an external event has occurred
which needs to be processed.
KB
Kilobyte. One thousand bytes.
147 - Glossary