Module 12 - I/O systems. The role of the operating system in computer I/O is to manage and control I/O operations and I/O devices. Although related topics appear in other chapters, here we bring together the pieces to paint a complete picture. In this chapter we describe I/O Structure, Devices, Device Drivers, Caching, and Terminal I/O. | Module 12: I/O Systems I/O hardwared Application I/O Interface Kernel I/O Subsystem Transforming I/O Requests to Hardware Operations Performance Operating System Concepts I/O Hardware Incredible variety of I/O devices Common concepts Port Bus (daisy chain or shared direct access) Controller (host adapter) I/O instructions control devices Devices have addresses, used by Direct I/O instructions Memory-mapped I/O Operating System Concepts Polling Determines state of device command-ready busy error Busy-wait cycle to wait for I/O from device Operating System Concepts Interrupts CPU Interrupt request line triggered by I/O device Interrupt handler receives interrupts Maskable to ignore or delay some interrupts Interrupt vector to dispatch interrupt to correct handler Based on priority Some unmaskable Interrupt mechanism also used for exceptions Operating System Concepts Interrupt-drive I/O Cycle Operating System Concepts Direct Memory Access Used to avoid programmed I/O for large data . | Module 12: I/O Systems I/O hardwared Application I/O Interface Kernel I/O Subsystem Transforming I/O Requests to Hardware Operations Performance Operating System Concepts I/O Hardware Incredible variety of I/O devices Common concepts Port Bus (daisy chain or shared direct access) Controller (host adapter) I/O instructions control devices Devices have addresses, used by Direct I/O instructions Memory-mapped I/O Operating System Concepts Polling Determines state of device command-ready busy error Busy-wait cycle to wait for I/O from device Operating System Concepts Interrupts CPU Interrupt request line triggered by I/O device Interrupt handler receives interrupts Maskable to ignore or delay some interrupts Interrupt vector to dispatch interrupt to correct handler Based on priority Some unmaskable Interrupt mechanism also used for exceptions Operating System Concepts Interrupt-drive I/O Cycle Operating System Concepts Direct Memory Access Used to avoid programmed I/O for large data movement Requires DMA controller Bypasses CPU to transfer data directly between I/O device and memory Operating System Concepts Six step process to perform DMA transfer Operating System Concepts Application I/O Interface I/O system calls encapsulate device behaviors in generic classes Device-driver layer hides differences among I/O controllers from kernel Devices vary in many dimensions Character-stream or block Sequential or random-access Sharable or dedicated Speed of operation read-write, read only, or write only Operating System Concepts Block and Character Devices Block devices include disk drives Commands include read, write, seek Raw I/O or file-system access Memory-mapped file access possible Character devices include keyboards, mice, serial ports Commands include get, put Libraries layered on top allow line editing Operating System Concepts Network Devices Varying enough from block and character to have own interface Unix and Windows/NT include socket interface Separates network .
