FIT2100 Lecture Notes - Lecture 1: Integer Overflow, Multiprocessing, Machine Code
30 May 2018
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LECTURE 01 - OPERATING SYSTEMS
What is an operating system?
•exploits the hardware resources of one or more processors!
•provides a set of services to system users!
•Manages secondary memory and I/O (input/output) devices on
behalf of its users!
What are the basic elements of a computer system?
•Processor!
◦Central Processing Unit (CPU)!
◦Controls the operation of the compute!
◦Performs the data processing functions!
•I/O Modules!
◦Moves data between the computer and external environments!
▪Storage (e.g. hard disk)!
▪Communications equipment!
▪Terminals!
•Main Memory!
◦Stores data and programs!
◦Volatile: contents of the memory is lost when the computer is
shut down!
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◦A.k.a. Real memory or primary memory or random access
memory!
•System Bus!
◦Provides for communication among processors, main memory,
and I?O modules!
◦Comprises of:!
▪Address bus!
▪Data bus!
▪Control bus!
Computer Components:
PC = Program counter
IR = Instruction register
MAR = Memory address register
MBR = Memory buffer register
I/O AR = Input/output address register
I/O BR = Input/output buffer register
How does a program get executed by a processor?
•Instruction Execution!
◦A program consists of a set of instructions stored in memory!
◦Processor reads (fetches) instructions from memory →
processor executes each instruction!
•Basic Instruction cycles!
◦Fetch Stage!
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▪The processor fetches the instruction from memory!
▪Program Counter (PC) holds address of the instruction to
be fetched next!
▪PC is incremented after each fetch in order to fetch the
next instruction!
•Execute Stage!
◦Fetched instructions are loaded into Instruction Register (IR)!
◦The processor interprets the instruction and performs the
required action!
◦Four categories of actions:!
▪Processor-memory!
▪Processor -I/O!
▪Data processing!
▪Control!
What are interrupts? Why a processor uses interrupts?
•Interrupt the normal sequencing of the processor!
•Provided to improve processor utilisation!
•Most IO devices are slower than the processor!
◦Processor must pause to wait for the I/O device to complete its
operation!
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Document Summary
What is an operating system? exploits the hardware resources of one or more processors provides a set of services to system users: manages secondary memory and i/o (input/output) devices on behalf of its users. Processor: central processing unit (cpu, controls the operation of the compute. I/o modules: moves data between the computer and external environments. Volatile: contents of the memory is lost when the computer is shut down. Real memory or primary memory or random access memory. Provides for communication among processors, main memory, and i?o modules: comprises of: A program consists of a set of instructions stored in memory. Processor reads (fetches) instructions from memory processor executes each instruction. Program counter (pc) holds address of the instruction to be fetched next. Pc is incremented after each fetch in order to fetch the next instruction. Fetched instructions are loaded into instruction register (ir) The processor interprets the instruction and performs the required action.
