Drivers

Question 1

what is a device driver? name 3 things they can do

Answer 1

a hardware-specific translator between userspace and hardware.
they play sound, display graphics, access a network

Question 2

why do most major OS support userspace drivers?

Answer 2

having drivers in userspace follows the microkernal approach

having them in user space means that if they crash the entire system doesn’t crash

Question 3

how are modern devices controlled by drivers? (i/o)

Answer 3

changing the value of their I/O registers
either memory-mapped or port-mapped

m-mapped:
registers are mapped into a memory address region and listen for specific addresses on the address bus
controlling the device amounts to just writing to memory

port-mapped: uses separate instructions for writing to I/O registers. often faked by mapping port addresses to memory addresses

Question 4

how does Unix view devices?

Answer 4

as files. 3 types

character devices:

• direct, unbuffered access
• used for real-time devices: sound, graphics

block devices:

• buffered access
• used for storage: HDD, tapes

network devices:

• packet-based, use specific system calls
• built on top of a socket abstraction

communicate with the driver by reading and writing to these files using system calls

Question 5

how does Windows view devices?

Answer 5

as files. 3 types

Direct I/O, buffered I/O and neither