Hardware Overview CS French Chapter 11

Main Functional Elements of a Computer System Input / Output (I/O) –to give out information –to take in data and instructions Storage –Memory (main storage) »holding current data and instructions Auxilliary Storage (not part of the main functional elements but included here to remind you that it is different from main storage) »supplement to main storage »less expensive, bigger capacity, non-volatile, slower. Processing –Arithmetic and Logic Unit (ALU) »calculations and comparisons –Control Unit »interprets and carries out instructions.

Elements of a Computer System Processor Control Unit ALU Memory (RAM) Input/ Output unit Computer Peripheral Devices Keyboard Screen Mouse Printer Plotter Modem Floppy disk drive Hard disk Compact disk Magnetic tape Network ‘card’ Classify ‘peripherals’ as input, output, auxialliary storage or communication devices! data bus

A Human as a Computer Name examples of each type of device! –Input –Output –Main Memory –Auxilliary Storage –Control Unit –ALU (Arithmetic and Logic Unit)

Input Devices Keyboard Mouse Bar code readers Voice data entry Sensors ( eg. temperature sensor) + Analog/Digital converter

Output Devices Printers –Ink Jet –Laser Plotters ( ) –Generally like large ink – jet printers Screen (VDU) Actuators + Digital/Analog converters (eg. robotic hand) Faster

On-line Process Control Digital Computer Analog to digital converter Digitally operated motor switch Vessel which must have its temperature controlled Electrical thermometer (sensor) Coolant tap driven by a motor (actuator) Input Output Digital control signal Analog data Fig 13.8

Main Storage (memory) Semi-conductor memory (RAM) –E.g. charged cells –Raandom Access Memory: RAM (constantly refreshed) –Battery backed RAM –ROM: Read Only Memory, set at manufacture

Auxilliary Storage Magnetic Disk –fixed/exchangable (online/off line) –hard/flexible (floppy) Magnetic Tape –cassette, cartridge, Digital Audio Tape Optical Disk –CDROM –WORM – write once read many times –EO – erasable optical – re-writable CD –DVDROM – very high capacity Solid State Backing storage devices Which of the above are direct access and which are serial access devices? (A serial access device requires that you read through all the preceeding data until you get to what you want. Think about serial/direct access to music)

Measurement of Storage Bit - smallest unit of storage Byte = 8 bits Kilobyte (Kb) 1024 bits (K = 2 10 = 1024) Megabyte (Mb) = 1024Kb Gigabyte = 1024 Mb 1000 is an acceptable approximation for K –eg 2Mb = 2,000,000 bytes

A Program to add up a set of numbers. The computer’s screen should look like this: Type in the numbers now (Remember to type 999 to stop) number =? 5 number =? 4 number =? 7 number =? 1 number =? 999 total = 17

Preparing the Human Computer Problem –How to add up a set of numbers and produce a total. Solution –a set of instructions in the computer’s own language (program) –english in the case of a ‘human computer’ Program is fed into your memory Instructions are obeyed –program ‘run’ or ‘executed’

The ‘Program’ 1. Start with total of zero. 2. Set a ‘signal’ value to Take a number from the input list. 4. If the number is equal to the signal value then go to instruction 7 5. Add the number to the total 6. Go back to instruction 3 7. Print the total 8. Stop

Testing the program(dry run) Program Trace