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Simon Fraser University
Computing Science
CMPT 300
Richard Vaughan

CMPT 300 – Chapter 1 – Introduction Operating System: ■ Presents a virtual machine, abstracted from the hardware ■ Hides and extends the computer hardware ■ Adds filesystems, processes, users, etc ■ manages computer resources ■ restricts access to the computer ■ consumes system resources (creating overhead) ■ OS provides a variety of services that programs can obtain using “system calls.” ■ Components: ■ OS: Kernel ■ Grey Area: Command interpreters, GUI ■ NOT OS: Compliers, Editors, Applications ■ Purpose: ■ Originally: Maximize utilization of computer ■ Now: Make computer easy to use, by abstraction (processes, files), libraries,… ■ Definitions: ■ Multiprogramming: Having different programs in memory and running them. ■ Timesharing: Ability of the computer to be used by multiple ppl simultaneously Computer Hardware ■ CPU: ■ Steps: Fetch instruction, Fetch data, Execute, Store results, Goto 1 ■ Components: Control unit, arithmetic logic unit, registers (instruction, PC, Stack Ptr, PSW) ■ Most communications with Memory ■ Full CPU Cycle: Interrupts: Happen on a clock interrupt or an I/O interrupt. When a process requires I/O, CPU sets up an interrupt handler, and blocks the process. The interrupt handler copies the information for the current program and runs the next program. When I/O for the last program is done, the interrupt handler runs the interrupt for the new program. ■ Memory: ■ Should be fast and cheap ■ Types: Registers, Cache, Main memory, Disk – All managed by memory management Two problems: ■ Protection Problem: Access to memory for diff programs needs to be under control ■ Relocation Problem: Addresses in memory need to start from the start address of the progrm ■ Base and Limit registers are used to solve both of these problems Speed of memory is affected by
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