Micro Computer Operating Systems Chapter 7 Terms

Front 1

Access Time

Back 1

The total time required to access data in secondary storage

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Blocking

Back 2

a storage-saving and I/O saving technique that groups individual records into a block that's stored and retrieved as a unit.

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buffers

Back 3

temporary storage areas residing in main memory, channels, and control units

Front 4

Channel Status Word (CSW)

Back 4

a data structure that contains information indicating the condition of the channel, including three bits for the three components of the I/O sub-system--one each channel, control unit, and device.

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C-LOOK

Back 5

a scheduling strategy for direct access storage devices that's an optimization of C-SCAN.

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C-SCAN

Back 6

a scheduling strategy for direct access storage devices that's an optimization of C-SCAN.

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cylinder

Back 7

a concept that describes a virtual tube that is formed when two or more read/write heads are positioned at the same track, at the same relative position, on their respective surfaces.

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dedicated devices

Back 8

a device that can be assigned to only one job at a time; it serves that job for the entire time the job is active.

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direct access storage device (DASD)

Back 9

any secondary storage device that can directly read or write to a specific place. Sometimes called a random access storage device.

Front 10

direct access memory DMA

Back 10

an I/O technique that allows a control unit to access main memory directly and transfer data without the intervention of the CPU.

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first come, first served FCFS

Back 11

the simplest scheduling algorithm for direct access storage devices that satisfies track requests in the order they are recieved.

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flash memory

Back 12

a type of nonvolatile memory used as a secondary storage device that can be erased and reprogrammed in blocks of data.

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Hamming Code

Back 13

an error-detecting, and error-correcting-code that greatly improves the reliability of the data, named after mathematician Richard Hamming, its inventor.

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I/O Channel

Back 14

a specialized programmable unit placed between the CPU and the control units, which synchronizes the fast speed of the CPU with the slow speed of the I/O device and vice versa, making it possible to overlap I/O operations with CPU operations.

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I/O channel program

Back 15

the program that controls the channels

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I/O control unit

Back 16

the hardware unit containing the electronic components common to one type of I/O device, such as disk drives.

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I/O device handler

Back 17

the module that processes the I/O interrupts, handles error conditions, and provides detailed scheduling algorithms that are extremely device dependant.

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I/O scheduler

Back 18

one of the modules of the I/O subsystem that allocates the devices, control units, and channels.

Front 19

I/O subsystem

Back 19

a collection of modules within the operating system that controls all I/O requests.

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I/O traffic controller

Back 20

one of the modules of the I/O subsystem that monitors the status of every device, control unit, and channel.

Front 21

interrecord gap (IRC)

Back 21

an unused space between records on a magnetic tape. It facilitates the tape's start/stop operations.

Front 22

interrupt

Back 22

a hardware signal that suspends execution of a program and activates the execution of a special program known as the interrupt handler.

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lands

Back 23

flat surface areas on the reflective layer of an optical disc. Each land is interpreted as a 1. Contrasts with pits, which are interpreted as 0's.

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LOOK

Back 24

a scheduling strategy for direct access storage devices that's used to optimize seek time. Sometimes known as the elevator algorithm.

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N-step SCAN

Back 25

a varation of the SCAN scheduling strategy for direct access storage devices that's used to optimize seek times.

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pits

Back 26

tiny depressions on the reflective layer of an optical disc. Each pit is interpreted as a 0.

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RAID

Back 27

acronym for redundant array of independent disks; a group of hard disks controlled in such a way that they speed read access of data on secondary storage devices and aid data recovery.

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rotational ordering

Back 28

an algorithm used to reorder record requests within tracks to optimize search time.

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SCAN

Back 29

a scheduling strategy for direct access storage devices that's used to optimize seek time. The most common variations are N-step SCAN and C-SCAN.

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search time

Back 30

the time it takes to rotate the disk from the moment an I/O command is issued until the requested record is moved under the read/write head. Also known as rotational delay.

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seek strategy

Back 31

a predetermined policy used by the I/O device handler to optimize seek times.

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sequential access medium

Back 32

any medium that stores records only in a sequential manner, one after the other, such as magnetic tapes.

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shared device

Back 33

a device that can be assigned to several active processes at the same time.

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shortest seek time first (SSTF)

Back 34

a scheduling strategy for direct access storage devices that's used to optimize seek time. The track requests are ordered so the one closest to the currently active track is satisfied first and the ones farthest away are made to wait.

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storage

Back 35

the place where data is stored in the computer system. Secondary storage is nonvolatile media, such as disks and flash memory. Primary storage is in main memory.

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stripe

Back 36

a set of consecutive strips across disks; the strips contain data bits and sometimes parity bits depending on the RAID level.

Front 37

track

Back 37

a path on a storage medium along which data is recorded.

Front 38

transfer rate

Back 38

the rate at which data is transferred from sequential access media.

Front 39

transfer time

Back 39

the time required for data to be transferred between secondary storage and main memory.

Front 40

universal serial bus (USB) controller

Back 40

the interface between the operating system device drivers, and applications that read and write to devices connected to the computer through the USB port.

Front 41

virtual device

Back 41

a dedicated device that has been transformed into a shared device through the use of spooling techniques.