Glossary 9Hhertz(Hz) A unit of frequency equal to one cycle per second.hexadecimalA number system that uses 16 as the base. (Place value indicates powers of 16.) Ituses the digits 0-9 and A-F. Used around computers because a byte (eight binarydigits) easily converts to a two digit hexadecimal number. Hexadecimal numbersare often indicated with the letter H, a dollar sign, or a subscripted 16 after thenumber. Compare binary, decimal.host adapterAn expansion board that serves as a controller for SCSI devices.hot keyCombination of two or three keys (such as Ctrl-Alt-D) that you presssimultaneously for a particular function.hot pluggingThe ability to add and remove devices to a computer while the computer is runningand have the operating system automatically recognize the change. The UniversalSerial Bus (see USB ) external bus standard supports hot plugging. This is also afeature of PCMCIA. Hot plugging is also called hot swapping.IIDEIntelligent Drive Electronics. A hard drive type that has controller electronics builtinto the drive and delivers high throughput.interfaceA connection that enables two devices to communicate.interruptA signal from part of a system, such as an I/O device, asking to use the CPU.Interrupts are hierarchical, which prevents interrupts from interrupting each other.(Whichever interrupt has higher priority makes the other interrupt wait.) When theCPU receives an interrupt signal, it saves what it is doing, processes the routineassociated with the interrupt, then returns to what it was doing.I/O addressInput-Output address. How the CPU sees an I/O port. It puts data into this addressor reads the data in it. The device at the other end of the I/O port gets the data fromthat address or puts the data there, respectively.
