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41 Cards in this Set

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Access Time
The total time required to access data in secondary storage
Blocking
a storage-saving and I/O saving technique that groups individual records into a block that's stored and retrieved as a unit.
buffers
temporary storage areas residing in main memory, channels, and control units
Channel Status Word (CSW)
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.
C-LOOK
a scheduling strategy for direct access storage devices that's an optimization of C-SCAN.
C-SCAN
a scheduling strategy for direct access storage devices that's an optimization of C-SCAN.
cylinder
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.
dedicated devices
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.
direct access storage device (DASD)
any secondary storage device that can directly read or write to a specific place. Sometimes called a random access storage device.
direct access memory DMA
an I/O technique that allows a control unit to access main memory directly and transfer data without the intervention of the CPU.
first come, first served FCFS
the simplest scheduling algorithm for direct access storage devices that satisfies track requests in the order they are recieved.
flash memory
a type of nonvolatile memory used as a secondary storage device that can be erased and reprogrammed in blocks of data.
Hamming Code
an error-detecting, and error-correcting-code that greatly improves the reliability of the data, named after mathematician Richard Hamming, its inventor.
I/O Channel
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.
I/O channel program
the program that controls the channels
I/O control unit
the hardware unit containing the electronic components common to one type of I/O device, such as disk drives.
I/O device handler
the module that processes the I/O interrupts, handles error conditions, and provides detailed scheduling algorithms that are extremely device dependant.
I/O scheduler
one of the modules of the I/O subsystem that allocates the devices, control units, and channels.
I/O subsystem
a collection of modules within the operating system that controls all I/O requests.
I/O traffic controller
one of the modules of the I/O subsystem that monitors the status of every device, control unit, and channel.
interrecord gap (IRC)
an unused space between records on a magnetic tape. It facilitates the tape's start/stop operations.
interrupt
a hardware signal that suspends execution of a program and activates the execution of a special program known as the interrupt handler.
lands
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.
LOOK
a scheduling strategy for direct access storage devices that's used to optimize seek time. Sometimes known as the elevator algorithm.
N-step SCAN
a varation of the SCAN scheduling strategy for direct access storage devices that's used to optimize seek times.
pits
tiny depressions on the reflective layer of an optical disc. Each pit is interpreted as a 0.
RAID
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.
rotational ordering
an algorithm used to reorder record requests within tracks to optimize search time.
SCAN
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.
search time
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.
seek strategy
a predetermined policy used by the I/O device handler to optimize seek times.
sequential access medium
any medium that stores records only in a sequential manner, one after the other, such as magnetic tapes.
shared device
a device that can be assigned to several active processes at the same time.
shortest seek time first (SSTF)
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.
storage
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.
stripe
a set of consecutive strips across disks; the strips contain data bits and sometimes parity bits depending on the RAID level.
track
a path on a storage medium along which data is recorded.
transfer rate
the rate at which data is transferred from sequential access media.
transfer time
the time required for data to be transferred between secondary storage and main memory.
universal serial bus (USB) controller
the interface between the operating system device drivers, and applications that read and write to devices connected to the computer through the USB port.
virtual device
a dedicated device that has been transformed into a shared device through the use of spooling techniques.