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 fast secondary cache. It is used as a secondary cache because 

SRAM is slower than SDRAM, but usually larger. Data is cached first to the faster primary 

cache, and then, when the primary cache is full, to the slower secondary cache. 

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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