I/O Hardware
COMP755 1
I/O Hardware
COMP755 Advanced Operating
Systems
I/O Devices
Disk Keyboard
hard Speakers
floppy Printer
CD Mouse
DVD Scanner
Monitor Game controller
Many, many more
I/O Controller
• Connects the I/O devices to the system.
• Communicates with the CPU and the RAM
over the bus.
• A single I/O controller may control multiple
devices.
• Most computers have several I/O
controllers.
• Actions are initiated by the CPU.
Differences in I/O Devices
• Complexity of control
• Unit of transfer
– stream of bytes
– large blocks
• Data representation
– Encoding schemes
• Error conditions
– Devices respond to errors differently
Differences in I/O Devices
• 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
Differences in I/O Devices
• Data rate
– May be differences of several orders of
magnitude between the data transfer rates
– High speed devices may run faster than the
CPU or bus can process the input.
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