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Chap. 10 I/O System (I/O Hardware (variety of I/O device: (storage,…
Chap. 10 I/O System
I/O Hardware
variety of I/O device:
storage
transmission
human-interface
common concepts - signals from I/Odevice interface with computer
port- connection point for device
bus-daily chain of shared direct access
controller(host adapter)- electronics that operate port, bus,device
I/O instruction control devices
devices have addresses:
direct I/O instruction
memory-mapped I/O
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
new devices talking already-implemented protocols need no extra work
device vary in many dimensions
character-stream/block
sequential/random-access
synchronous/asynchronous
sharable/dedicated
speed of operation
read-write,read-only/write-only
improving performance
reduce number of context switches
reduce data copying
use DMA
use smarter hardware devices
transforming I/O requests to hardware operations
consider reading a file from disk for a process:
determine device holding file
translate name to device representation
physically read data from disk into buffer
make data available to requesting process
return control to process
performance
I/O a major factor in system performance
demands CPU to execute device driver, kernel I/O cde
context switches due to interupts
data copying
network traffic especially stressful.