the total time required to access data in secondary storage
access time
a storage-saving and I/O-saving technique that groups individual records into a block that’s stored and retrieved as a unit
blocking
temporary storage areas residing in main memory, channels, and control units.
buffers
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 for the channel, control unit, and device.
Channel Status Word (CSW)
a scheduling strategy for direct access storage devices that’s an optimization of C-SCAN.
C-LOOK
a scheduling strategy for direct access storage devices that’s used to optimize seek time. It’s an abbreviation for circular-SCAN.
C-SCAN
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
cylinder
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.
dedicated device
any secondary storage device that can directly read or write to a specific place. Sometimes called a random access storage device
direct access storage device (DASD)
an I/O technique that allows a control unit to access main memory directly and transfer data without the intervention of the CPU.
direct memory access (DMA)
the simplest scheduling algorithm for direct access storage devices that satisfies track requests in the order in which they are received
first-come, first-served (FCFS)
a type of nonvolatile memory used as a secondary storage device that can be erased and reprogrammed in blocks of data
flash memory
an error-detecting and error-correcting code that greatly improves the reliability of data, named after mathematician Richard Hamming, its inventor.
Hamming code
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
the program that controls the channels.
I/O channel program
the hardware unit containing the electronic components common to one type of I/O device, such as a disk drive
I/O control unit
the module that processes the I/O interrupts, handles error conditions, and provides detailed scheduling algorithms that are extremely device dependent.
I/O device handler
one of the modules of the I/O subsystem that allocates the devices, control units, and channels.
I/O scheduler
a collection of modules within the operating system that controls all I/O requests
I/O subsystem
one of the modules of the I/O subsystem that monitors the status of every device, control unit, and channel.
I/O traffic controller
an unused space between records on a magnetic tape. It facilitates the tape’s start/stop operations.
interrecord gap (IRG)
a hardware signal that suspends execution of a program and activates the execution of a special program known as the interrupt handler.
interrupt
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 0s
lands
a scheduling strategy for direct access storage devices that’s used to optimize seek time. Sometimes known as the elevator algorithm.
LOOK
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Chapter 1103
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Chapter 25
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Review Questions13
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Chapter 361
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Chapter 441
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Key Terms79
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Chapter 527
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Chapter 5 key terms19
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Chapter 3 Key Terms32
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Chapter 4 Key Terms37
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Chapter 2 Key Terms18
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Chapter 1 Key Terms32
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Chapter 645
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Chapter 6 Key Terms25
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Chapter 756
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Chapter 7 Key Terms42
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Chapter 8 Key Terms33
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Chapter 847
