Computer Organization

The Five Hardware Units

General purpose computers use the "Von Neumann" architecture

Also referred to as "stored program" architecture

CPU

MainMemory(RAM)

InputUnit

OutputUnit

SecondaryMemory

Central Processing Unit

Control unit – directs the operation of the rest of the computer

Arithmetic-Logic Unit – performs calculations and comparisons

Communicates via "system bus" with other components

ControlUnit

Arithmetic-LogicUnit

Central Processing Unit

System bus

Main MemoryComposed of a sequence of "cells" or "words," each composed of "bits"

Each cell has a numeric address

The contents of any cell can be retrieved or stored in the same amount of time

Thus, "Random Access Memory"

Input Unit

We need some way to get data from the outside world into the computer

Examples: Keyboard

Mouse

Microphone

Graphics tablet

Scanner

Modem/network card

Output Units

Likewise, we need a way to communicate to the outside world

Screen

Printer

Speakers

Modem/network interface

Secondary Memory

High capacity, long-term storage

Examples Hard disks

Optical drives (CD-ROM, DVD-ROM)

Flash drives

Next level is tertiary or archival storage Backup tape drives

Floppy disks

The Memory HierarchyRegisters – locations in the CPU for current

computations

Cache – very fast memory for frequently used values

Main memory – fast memory used for currently executing programs and their data

Secondary memory – slower (but very large) memory used for long term storage of programs and data

Tertiary memory – slowest (but largest) memory used for backups and archival storage

Memory Persistence

Volatile memory – memory that only works when electrical power is supplied

Registers, cache, and main memory (RAM)

Non-volatile memory – memory that retains its contents when power is off

Hard drives, flash drives, optical drives, magnetic tape

Memory access types

Read-write – data can be stored and retrieved any number of times (registers, cache, RAM)

Read-only (ROM) – contents cannot be altered

Storage DensitiesUnits

1 byte = 8 bits = space to store 1 character

1 Megabyte (MB) = 220 = 1,048,576 bytes

1 Gigabyte (GB) = 230 = 1,073,741,824 bytes

1 Terabyte (TB) = 240 = 1,099,511,627,776 bytes

ExamplesA 300 page book holds approximately 1,500,000 characters

DVD-5 format disk holds 4.7 GB of data

30 GB IPod holds 7500 4 minute songs

Dual layer Blu-ray format disks hold 50 GB of data (holds 9 hours of HD video or 23 hours of SD video)

US Library of Congress holds 20 TB of data

Memory Cost

Prices are retail consumer-oriented

512MB RAM chip – 12 cents per MB

200GB hard disk – 0.054 cents per MB

400GB hard disk – 0.041 cents per MB

(prices gathered on 9/12/06)

Assignment

How Computers Work, Chapters 1-3 and 5