day1 review

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users view

single user

multiple user

multiple users conneccted to servers

mobille computers

system’s view

resource allocator

control program

kernal is the core part

system program and application programs

mobile os include middleware

OS structure

multiprogramming

resources are utilised effectively

time sharing

day2

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modern OS are interrupt-driven

error/interrupt in a program is trap/exception eg:hardware interrupt- access a memory loc not allowed right now

Interrupt service droutine(ISR) is provided to deal with the interrupt

dual mode and multi-mode operation

to protect os from wrong users

dual

2 seperate modes : user mode and kernal mode(supervisor,system,privileged mode) a bit called the mode bit is added to the hardware of the comp to indicate the current mode: kernel(0) and user(1)

multi mode

eg: I/O control,switch kernal mode,time management, interrupt management supports vitrualization

more options than user moder but less options than kernal mode

cpu’s that support virtuallization frequently have a separate mode to indicate when the virtual machine manager(VMM)

Timer

a timer can be set to interrupt yhe computer after a task period.

a variable timer is generally implemented by a fixed-rate clock and a counter the OS sets the counter

instrutions that modify the content of the timer are privileged

use : prevent the prog from running too long