Appendix I: Glossary
A26361-D1691-Z120-1-7619, Edition 1 57
IRQ (Interrupt Request): an electronic request that runs from a hardware device to the CPU. The
interrupt controller assigns priorities to incoming requests and delivers them to the CPU. It is
important that there is only one device hooked up to each IRQ line; doubling up devices on IRQ
lines can lock up your system. Plug-n-Play operating systems can take care of these details for you.
ISA (Industry Standard Architecture): a slower 8- or 16-bit bus (data pathway).
Latency: the amount of time that one part of a system spends waiting for another part to catch up.
This is most common when the system sends data out to a peripheral device, and it waiting for the
peripheral to send some data back (peripherals tend to be slower than onboard system
components).
Mirroring: see RAID.
NVRAM: ROM and EEPROM are both examples of Non-Volatile RAM, memory that holds its data
without power. DRAM, in contrast, is volatile.
OEMs (Original Equipment Manufacturers): Compaq or IBM package other companies’
motherboards and hardware inside their case and sell them.
Parallel port: transmits the bits of a byte on eight different wires at the same time (that is, in parallel
form, eight bits at the same time).
PCI (Peripheral Component Interconnect): a 32 or 64-bit local bus (data pathway) which is faster
than the ISA bus. Local buses are those which operate within a single system (as opposed to a
network bus, which connects multiple systems).
PCI PIO (PCI Programmable Input/Output) modes: the data transfer modes used by IDE drives.
These modes use the CPU for data transfer (in contrast, DMA channels do not). PCI refers to the
type of bus used by these modes to communicate with the CPU.
PCI-to-PCI bridge: allows you to connect multiple PCI devices onto one PCI slot.
Pipeline burst SRAM: a type of RAM that can maintain it’s data as long as power is provided to the
memory chips. In this configuration, SRAM requests are pipelined, which means that larger packets
of data are sent to the memory at one time, and acted upon quickly. This type of SRAM operates at
bus speeds higher than 66MHz.
Pipelining: improves system performance by allowing the CPU to begin executing a second
instruction before the first is completed. A pipeline can be likened to an assembly line, with a given
part of the pipeline repeatedly executing a set part of an operation on a series of instructions.
PM timers (Power Management timers): software timers that count down the number of seconds
or minutes until the system times out and enters sleep, suspend, or doze mode.
PnP (Plug-n-Play): a design standard that has become ascendant in the industry. Plug-n-Play
devices require little set-up to use. Novice end users can simply plug them into a computer that is
running on a Plug-n-Play aware operating system (such as Windows 98), and go to work. Devices
and operating systems that are not Plug-n-Play require you to reconfigure your system each time
you add or change any part of your hardware.
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