聊城大学计算机学院计算机操作系统（1）英文课件 Chapter11.ppt

I/O Management and Disk Scheduling Chapter 11 Categories of I/O Devices Human readable Used to communicate with the user Printers Video display terminals Display Keyboard Mouse Categories of I/O Devices Machine readable Used to communicate with electronic equipment Disk and tape drives Sensors Controllers Actuators Categories of I/O Devices Communication Used to communicate with remote devices Digital line drivers Modems Differences in I/O Devices Data rate May be differences of several orders of magnitude between the data transfer rates Differences in I/O Devices Application Disk used to store files requires file management software Disk used to store virtual memory pages needs special hardware and software to support it Terminal used by system administrator may have a higher priority Differences in I/O Devices Complexity of control Unit of transfer Data may be transferred as a stream of bytes for a terminal or in larger blocks for a disk Data representation Encoding schemes Error conditions Devices respond to errors differently Performing I/O Programmed I/O Process is busy-waiting for the operation to complete Interrupt-driven I/O I/O command is issued Processor continues executing instructions I/O module sends an interrupt when done Performing I/O Direct Memory Access (DMA) DMA module controls exchange of data between main memory and the I/O device Processor interrupted only after entire block has been transferred Relationship Among Techniques Evolution of the I/O Function Processor directly controls a peripheral device Controller or I/O module is added Processor uses programmed I/O without interrupts Processor does not need to handle details of external devices Evolution of the I/O Function Controller or I/O module with interrupts Processor does not spend time waiting for an I/O operation to be performed Direct Memory Access Blocks of data are moved into memory without involving the processor Processor involved at beginning and end only Evolution of the I/O