Begin Datablast GCSE Computing. Computer Systems Define a computer system Describe the importance of computer systems Explain the need for reliability

Begin DatablastGCSE Computing

Computer Systems

•Define a computer system

•Describe the importance of computer systems

•Explain the need for reliability

•Explain the need for professional standards

•Ethical, environmental, legal issues

CPU

TopicTopic Key PointsKey Points

PurposeFetch, Decode, Execute

instructions

FunctionFetch - Decode - Execute

Cycle

PerformanceClock speed, Caches and

Cores

Binary Logic

•Why use binary?

GateGate SymbolSymbol

AND

OR

NOT

RAM vs ROM


RAMCurrently running programs,

currently used data

ROM Startup instructions

IssuesVolatile vs non-volatile

Size

Memory


Cache Buffer, small, quick

RAM Main memory

Virtual Memory Hard drive, large, slooow

Device Types


InputKeyboard, Mouse, Webcam,

Mic

Output Speaker, Monitor, Printer

Storage Magnetic, Optical, Solid State

Processing CPU

Communication Modem, Router

Storage Devices


Magnetic HDD, Magnetic Tape

Optical CD, DVD, BluRay

Solid State Memory card, USB stick, SSD

Operating Systems

•User Interface

•Memory Management

•Peripheral Management

•Multi-tasking

•Security

Utility Programs


Security Antivirus, spyware, firewalls

Disk organisation

Defragmentation, formatting, FTP

System Maintenance

System cleanup, automatic updates, system info

Application Software

Issue vs IssueIssue vs Issue

Off the shelf Bespoke

Open Source Proprietary

Binary Numbers

•Bit - Nibble - Byte - KB - MB - GB - TB

•Convert Binary <=> Denary

•Binary Addition

•Overflow Errors

Hexadecimal

•Convert Binary <=> Hexadecimal

•Convert Denary <=> Hexadecimal

•Advantages of Hexadecimal

Representing Characters


How it works Lookup table of values

Character Sets ASCII, Unicode

Bits per character

Add 1 bit, DOUBLE the range

Representing Images


How it works Pixel colours in binary

MetadataHeight, width, resolution,

colour depth

File sizeResolution - Pixel density

Colour depth - bits per pixel

Representing Sound


How it works Sound samples in binary

Sample RateFrequency of samples, Equivalent to resolution

Bit DepthBits per sample,

Equivalent to colour depth

Representing Instructions


Machine Code Numeric values for instructions

OpcodesCode for the Operation

e.g. add, store, load, branch

OperandAddress to be operated on

e.g. #0060

DBMS


DatabasePersistent, organised store of

data

DBMS

Database Management System

Separates the program from the data

PurposeCreate, maintain and

interrogate DB

Database Components


Tables Entities, store of data

FormsInterface for the table, easy to

use, view/add/edit records

Queries Search / interrogate data

ReportsOrganised layout, snapshot of

the data

Relational Databases


Primary Key Unique for each record

Foreign Key Links to another table

Data Redundancy

Avoid duplicating dataOnly update one record

Networks


Standalone Not networked

LANLocal Area Network

One SiteBespoke Cabling

WANWide Area Network

Separate SitesUses Telecomms Infrastructure

Network Hardware


Network Card Wired, wireless, bluetooth

Modem Connect digital and analogue

Hub / RouterCommunicate between

computers

Wifi Router, built in, dongle

Topologies

TopicTopic ProsPros ConsCons

Ring Few cables Easy to break

BusIndividual

machines won’t break network

Central bus can break network

Star Most reliable Lots of cabling

Network Terms


IP AddressAddress for each machine

e.g. 192.168.0.101

MAC Address

Permanent address for each device

e.g. ethernet, wifi and bluetooth

PacketsSplit data into small parts to

send. Why?

DNSLookup table.

google.com => 217.143.12.98

Network Security


User Access Levels

Installing software, accessing key files

Password Policies

Avoid obvious passwords, change regularly?

Encryption HTTP vs HTTPS

Filtering Blocked websites

Network Policies


Acceptable Use

You signed one!

Disaster Recovery

Keeping the business going

Failover Redundant servers

BackupOnsite, offsite, batch,

sequential...

Webpages


HTMLRendering in web browsers, <tags>, consistent standard

Filetypes JPG, GIF, MPG, MP3, PDF

Lossless Compression

Identical when recreating the file

Small size savingLossy

CompressionSome data - and quality - lost

Significantly smaller

Programming Terms


Sequence List of instructions in order

Selection If statement

Iteration While loop, For loop

Variables Name, Type, Value

Data Types


Char & String Text

Integer Whole Number

Real or FloatDecimal Number

(Decimal Fraction)

Boolean True or False

Programming Languages

TopicTopic ExampleExample Key PointsKey Points

High Level

if score > 200:print(“You win!”)

Cross-platformEasier to

read/writeAssembl

y Languag

e

LDA 36Opcode & Operand

Hardware specificEasier to

read/write *than machine code*

Machine Code

0110 0110Opcode & Operand

Hardware specificWhat the

processor uses

Translators


Compiler

From High Level to Machine Code

Batch job - find all syntax errors

Quicker to run once compiled

Interpreter

From High Level to Machine Code

Step-by-step - Stop at first error

Quicker to edit and test

AssemblerFrom Assembler to Machine

CodeOne-to-one translation

Testing


StrategiesTest the boundaries

Valid, Invalid, Extreme

Syntax ErrorMis-typedWon’t run

Logic ErrorValid syntax - it runs

Doesn’t do what you intended

Documents

Begin Datablast GCSE Computing. Computer Systems Define a computer system Describe the importance of computer systems Explain the need for reliability