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Kernel I/O Subsystem Kernel I/O Subsystems responsible to provide many services related to I/O. Following are some of the services provided. Scheduling - Kernel schedules a set of I/O requests to determine a good order in which to execute them. When an application issues a blocking I/O system call, the request is placed on the queue for that device. The Kernel I/O scheduler rearranges the order of the queue to improve the overall system efficiency and the average response time experienced by the applications. Buffering - Kernel I/O Subsystem maintains a memory area known as buffer that stores data while they are transferred between two devices or between a devices with an application operation. Buffering is done to cope with a speed mismatch between the producer and consumer of a data stream or to adapt between devices that have different data transfer sizes. Caching - Kernel maintains cache memory which is region of fast memory that holds copies of data. Access to the cached copy is more efficient than access to the original. Spooling and Device Reservation - A spool is a buffer that holds output for a device, such as a printer, that cannot accept interleaved data streams. The spooling system copies the queued spool files to the printer one at a time. In some operating systems, spooling is managed by a system daemon process. In other operating systems, it is handled by an in kernel thread. Error Handling - An operating system that uses protected memory can guard against many kinds of hardware and application errors. TUTORIALS POINT Simply Easy Learning Page 73
Device driver Device driver is a program or routine developed for an I/O device. A device driver implements I/O operations or behaviors on a specific class of devices. For example a system supports one or a number of multiple brands of terminals, all slightly different terminals may have a single terminal driver. In the layered structure of I/O system, device driver lies between interrupt handler and device independent I/O software. The job of a device driver is following. To accept request from the device independent software above it. To see to it that the request is executed. How a device driver handles a request is as follows: Suppose a request comes to read a block N. If the driver is idle at the time a request arrives, it starts carrying out the request immediately. Otherwise, if the driver is already busy with some other request, it places the new request in the queue of pending requests. TUTORIALS POINT Simply Easy Learning Page 74
Page 1 and 2:
Operating System Tutorial
Page 3 and 4:
ABOUT THE TUTORIAL Operating System
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Multiprogramming ..................
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Clocks ............................
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Following are some of important fun
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CHAPTER 2 Types of Operating System
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Distributed operating System Distri
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Real Time operating System Real tim
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Program execution Operating system
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Error handling Error can occur anyt
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Increased performance as a new job
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Multiprogramming When two or more p
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Spooling Spooling is an acronym for
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Program A program by itself is not
Page 29 and 30: Process Control Block, PCB Each pro
Page 31 and 32: CHAPTER 6 Operating System Process
Page 33 and 34: Two State Process Model Two state p
Page 35 and 36: Running process may become suspende
Page 37 and 38: Context Switch A context switch is
Page 39 and 40: First Come First Serve (FCFS) Jo
Page 41 and 42: Priority Based Scheduling Each p
Page 43 and 44: Multi Queue Scheduling Multiple
Page 45 and 46: Difference between Process and Thre
Page 47 and 48: Types of Thread Threads are impleme
Page 49 and 50: Multithreading Models Some operatin
Page 51 and 52: Difference between User Level & Ker
Page 53 and 54: Instructions and data to memory add
Page 55 and 56: Logical versus Physical Address Spa
Page 57 and 58: Memory Allocation Main memory usual
Page 59 and 60: Paging External fragmentation is av
Page 61 and 62: Address generated by CPU is divided
Page 63 and 64: Virtual memory is commonly implemen
Page 65 and 66: Step Description Step 1 Check an in
Page 67 and 68: Page Replacement Algorithm Page rep
Page 69 and 70: Least Recently Used (LRU) algorithm
Page 71 and 72: I/O port An I/O port typically cons
Page 73 and 74: I/O devices I/O Devices can be cate
Page 75 and 76: 4 Disk controller sends each byte t
Page 77 and 78: CHAPTER 12 I/O Software This sectio
Page 79: Clocks Clocks are also called timer
Page 83 and 84: File Type File type refers to the a
Page 85 and 86: Space Allocation Files are allocate
Page 87 and 88: Authentication Authentication refer
Page 89 and 90: Program Threats Operating system's
Page 91 and 92: Computer Security Classifications A
Page 93 and 94: Components of Linux System Linux Op
Page 95 and 96: Basic Features Following are some o
Page 97: APPENDIX A About tutorialspoint.com
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