Glossary of Acronyms

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IC - Integrated Circuit. A chip.

ICache - Instruction Cache. Part of the L1 or Primary Cache. A fast local memory that holds the instructions to be executed. When a program tries to access an instruction that is not yet in the cache, the CPU must wait until hardware fetches the desired instruction from another cache, or memory itself down stream. These stalls in the fetch/decode unit of the Pentium Pro Processor are typically overlapped by the other units that are processing independently.

IDE - Integrated Disk Electronics. A type of hard disk technology pioneered by Compaq and Conner that embedded a controller onto the hard disk PCB (Printed Circuit Board) while maintaining computability with the register level commands sent by the computer's INT 13 routines. IDE drives are configured and appear to the computer like standard ST506 drives . IDE is the least expensive technology with support usually built into the mainboard. An IDE disk is connected to the mainboard or interface card through a flat ribbon cable. Rather than invent a new interface, the signals in the IDE cable simply duplicate the activity on the ISA bus itself. Classic IDE supported two harddisks of 528 megabytes or less. An IDE interface cable has two plugs that can be attached to the two disks. Also known as ATA.

INT13 - A basic BIOS subroutine that controls the function and configuration of the hard disk drive. Continued reliance on the unchanged INT13 routine inherently creates certain hard drive limiting factors, including a problem with more than two hard drives and BIOS/OS limits to recognizing more than 1024 cylinders, 16 heads, and 63 sectors per track. This creates the so called 504 MB barrier since a sector holds only 512 bytes. As calculated:

1024 (Cylinders) X 16 (Heads) X 63 (Sectors/Track) X 512 (Bytes/Sector) = 528,482,304 Bytes

I/O - Input/Output. This is an abbreviation for input/output, which applies to any communication activity both inside and outside the computer. Same as the Bus, or a common set of wires that connect the computer devices and chips together. Some of these wires are used to transmit data, some send housekeeping signals, like the clock pulse, and some transmit numbers (the address) that identifies a particular device or memory location. The bus speed is determined by the clock speed or cycles per second.

IPL - Initial Program Load. Another term for the Bootstrap Loader Program where the BIOS code tells the microprocessor to jump to the section of code that tells the chip how to read the first sector on the disk.

IrDA - Infrared. A type of port available on Pentium systems that allows the transfer of files to and from portable devices such as laptops through transmitters and receivers.

IRP - I/O Request Packet. Data structures that drivers sue to communicate with each other.

IRQ - Interrupt Request Lines. Hardware lines over which devices can send signals to get the attention of the processor when the device is ready to accept or send information. Typically, each device connected to the computer uses a separate IRQ. The most important difference between the CPU/Memory local bus and the I/O bus is the presence of IRQ wires. The I/O bus has 15 separate IRQ wires. When a device generated an interrupt, the CPU hardware stops running an ordinary program and jumps to an interrupt handling routine in the device driver. The interrupt may signal that a previous request is complete and the device can now start a new request, that data has arrived that needs to be read, or that an error has been detected on an idle device. Any device on the I/O bus can request an interrupt by placing a signal on one of the 15 IRQ wires. If more than one IRQ signal is received at the same time, the chip set on the mainboard has to select the one with the highest priority to process first. The CPU is interrupted (by sending a signal on its one wire) and the chip set then transfers the identity of the IRQ level to be processed. Each IRQ wire goes to every slot in the I/O bus. An adapter card is configured (physically with switches or logically with a utility) to use a specific IRQ value. The newer bus architectures, such as MCA, EISA, and PCI, use circuitry that allows two devices to share the same interrupt.

Physical connections between external hardware devices and the interrupt 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, 8 IRQ lines, numbered IRQ 0 through IRQ7 are included. On the AT and PS/2 systems, 16 IRQ lines are numbered IRQ 0 through IRQ 5. IRQ lines must be used only by a single adapter in the ISA bus systems, but Micro Architecture (MCA) adapters can share interrupts.

ISA - Industry Standard Architecture. A type of computer bus design or architecture of the IBM PC/AT. An ISA bus is a 16 bit interface that runs at 8 MHz. The 8-bit version came on the original PC and the AT, but the latter uses an extension to make it 16-bit. It has a maximum data transfer rate of about 8 megabits per second on an AT, which is actually well above the capability of disk drives, or most network and video cards. The average data throughput is around a quarter of that. Its design makes it difficult to mix 8- and 16-bit RAM or ROM within the same 128K block of upper memory; an 8-bit VGA card could force all other cards in the same (C000-DFFF) range to use 8 bits as well, which was a common source of inexplicable crashes where 16-bit network card were involved.

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Compiled by Scott McArdle, MagnaCom Limited. I hope this list has helped you and if there is an item that should be on this list, please let me know. Thanks. PS, I've spent 100's of hours maintaining this list, please don't be a LAMER.