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Application I/O Interface Application I/O Interface represents the structuring techniques and interfaces for the operating system to enable I/O devices to be treated in a standard, uniform way. The actual differences lies kernel level modules called device drivers which are custom tailored to corresponding devices but show one of the standard interfaces to applications. The purpose of the device-driver layer is to hide the differences among device controllers from the I/O subsystem of the kernel, such as the I/O system calls. Following are the characteristics of I/O interfaces with respected to devices. Character-stream / block - A character-stream device transfers bytes in one by one fashion, whereas a block device transfers a complete unit of bytes. Sequential / random-access - A sequential device transfers data in a fixed order determined by the device, random-access device can be instructed to seek position to any of the available data storage locations. Synchronous / asynchronous - A synchronous device performs data transfers with known response time where as an asynchronous device shows irregular or unpredictable response time. Sharable / dedicated - A sharable device can be used concurrently by several processes or threads but a dedicated device cannot be used. Speed of operation - Device speeds may range from a few bytes per second to a few gigabytes per second. Read-write, read only, or write only - Some devices perform both input and output, but others support only one data direction that is read only. TUTORIALS POINT Simply Easy Learning Page 71
Clocks Clocks are also called timers. The clock software takes the form of a device driver though a clock is neither a blocking device nor a character based device. The clock software is the clock driver. The exact function of the clock driver may vary depending on operating system. Generally, the functions of the clock driver include the following. S.N. Task Description 1 Maintaining the time of the day The clock driver implements the time of day or the real time clock function. It requires incrementing a counter at each clock tick. 2 Preventing processes from running too long As a process is started, the scheduler initializes the quantum counter in clock ticks for the process. The clock driver decrements the quantum counter by 1, at every clock interrupts. When the counter gets to zero, clock driver calls the scheduler to set up another process. Thus clock driver helps in preventing processes from running longer than time slice allowed. 3 Accounting for CPU usage Another function performed by clock driver is doing CPU accounting. CPU accounting implies telling how long the process has run. 4 Providing watchdog timers for parts of the system itself Watchdog timers are the timers set by certain parts of the system. For example, to use a floppy disk, the system must turn on the motor and then wait about 500msec for it to come up to speed. TUTORIALS POINT Simply Easy Learning Page 72
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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
Page 27 and 28: 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: CHAPTER 12 I/O Software This sectio
Page 81 and 82: Device driver Device driver is a pr
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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