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Direct Memory Access (DMA) Many computers avoid burdening the main CPU with programmed I/O by offloading some of this work to a special purpose processor. This type of processor is called, a Direct Memory Access (DMA) controller. A special control unit is used to transfer block of data directly between an external device and the main memory, without intervention by the processor. This approach is called Direct Memory Access (DMA). DMA can be used with either polling or interrupt software. DMA is particularly useful on devices like disks, where many bytes of information can be transferred in single I/O operations. When used with an interrupt, the CPU is notified only after the entire block of data has been transferred. For each byte or word transferred, it must provide the memory address and all the bus signals controlling the data transfer. Interaction with a device controller is managed through a device driver. Handshaking is a process between the DMA controller and the device controller. It is performed via wires using terms DMA request and DMA acknowledge. Step Description 1 Device driver is instructed to transfer disk data to a buffer address X. 2 Device driver then instruct disk controller to transfer data to buffer. 3 Disk controller starts DMA transfer. TUTORIALS POINT Simply Easy Learning Page 67
4 Disk controller sends each byte to DMA controller. 5 DMA controller transfers bytes to buffer, increases the memory address, decreases the counter C until C becomes zero. 6 When C becomes zero, DMA interrupts CPU to signal transfer completion. TUTORIALS POINT Simply Easy Learning Page 68
Page 1 and 2:
Operating System Tutorial
Page 3 and 4:
ABOUT THE TUTORIAL Operating System
Page 5 and 6:
Multiprogramming ..................
Page 7 and 8:
Clocks ............................
Page 9 and 10:
Following are some of important fun
Page 11 and 12:
CHAPTER 2 Types of Operating System
Page 13 and 14:
Distributed operating System Distri
Page 15 and 16:
Real Time operating System Real tim
Page 17 and 18:
Program execution Operating system
Page 19 and 20:
Error handling Error can occur anyt
Page 21 and 22:
Increased performance as a new job
Page 23 and 24: Multiprogramming When two or more p
Page 25 and 26: 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: I/O devices I/O Devices can be cate
Page 77 and 78: CHAPTER 12 I/O Software This sectio
Page 79 and 80: Clocks Clocks are also called timer
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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