1 COMS 161 Introduction to Computing Title: Computing Basics Date: September 15, 2004 Lecture Number: 10

2 Announcements May miss later part of office hours today

3 Review Digitization Computer System Basics –Finite discrete states –Instructions cause state transitions –Fetch-execute cycle –Indirection provides flexibility

4 Outline Computer System Basics

5 Computer Systems Slight variant of the add instruction add val1, val2, val3 –Fetch the values (operands) to be added Read the memory at the location of val2 Put the value on one of the adder inputs Read the memory at the location of val3 Put the value on the other adder inputs –Execute the add –Put result in memory at location val1

6 Seemingly simple instruction like add –Require several simpler steps to execute As complex as computers seem, they still do simple things –Moving data from one place to another –Simple arithmetic operations Illusion of complexity –Perpetuated by the speed of simple operations Computer Systems

7 Composed of two major items –Hardware Electronic devices that perform specific tasks Two basic groups –Processing unit »The brain of the computer –Peripherals –Software Programs the hardware executes Computer Systems

8 Basic Computer Components All computers, large or small, have the same basic parts –Input/output (I/O) –Processor –Memory The software (instructions for the processor) are stored in the same memory with the data

9 Basic Computer Components The main parts of a computer are on the motherboard

10 The von Neumann Architecture All modern computers follow the logical model of computing called the von Neumann Architecture: Stored-program design (program instructions in memory) Computer organized into three main parts: –CPU –Main Memory Primary storage –I/O Subsystem Input and output devices (peripherals) Secondary storage (mass storage) von Neumann’s 1945 paper can be found at

11 The CPU

12 Central Processing Unit The CPU has two main components: 1.Control unit Implements the program interpretation cycle –Determines which instruction to next fetch from memory –Decodes the instruction –Makes sure that it gets executed Coordinates activities of all other parts of the computer 2.ALU (arithmetic-logic unit) Actually executes the programmed instructionsFetchFetchDecodeDecode ExecuteExecute

13 Central Processing Unit The Intel Pentium-M

14 Central Processing Unit A wafer containing several hundred CPU’s

15 Work area for the CPU –Contains millions of storage cells 256MBytes, 512MBytes, 1GByte –Information in memory Program instructions Numbers for arithmetic Text character codes (ASCII) Digital codes representing pictures … Main Memory

16 SIMMS –Single In-Line Memory Modules –Small circuit boards holding memory chips Main Memory

17 Composed of individual memory cells Cells are grouped into words Words are accessed via a unique address Memory Control Unit Data Bus Address Bus 0x3550 0x3554 0x3558 0x355c 0x3560 0x3564 0x3568 0x356c unique memory address Main Memory

18 Main Memory Main memory is generally Random Access Memory (RAM) –Readable –Writable –General use programs and data –Volatile disappears when powered off Computers also generally have Read Only Memory (ROM) –Readable –Permanent (not writable) –Special purpose boot instructions basic operations (BIOS) –Non-volatile unaffected by power-off –ROM is not part of main memory

19 Without power everything in main memory is lost How does a computer start itself? Booting

20 Special start-up instructions are stored in ROM –BIOS (basic input-output system) Booting

21 BIOS loads the operating system from disk into main memory –After instructions are loaded into memory, the CPU executes them Booting