COMP 3430 Operating Systems
I/O devices
March 9th, 2022
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By the end of today’s lecture, you should be able to:
▶ Explain how an operating system provides an abstraction around hardware devices.
▶ Compare and contrast I/O scheduling policies and process scheduling policies.
The Rocket Book (Public Domain)
Let’s take a look at the course schedule.
Implement an interface
Let’s “implement” an interface for a webcam. Remember: devices are files. “Everything” is a file.
My whole life is a file. (Pixabay License)
Everyone, answer in chat: what system calls operate on files?
Teams: What should a webcam do when you call file system calls on it?
▶ open ▶ read ▶ write ▶ close ▶ lseek
Alternative approaches
▶ Everything is a file in UNIX/Linux (mostly).
▶ Windows?
▶ Specific OS-level APIs for devices.
▶ Operating systems hide device details from software. ▶ Different operating systems do it differently.
▶ I/O operations can be scheduled similarly to processes.
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