Begin Datablast
GCSE 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
Topic
Key Points
Purpose
Fetch, Decode, Execute
instructions
Function
Fetch - Decode - Execute Cycle
Performance
Clock speed, Caches and Cores
Binary Logic
• Why use binary?
Gate
AND
OR
NOT
Symbol
RAM vs ROM
Topic
Key Points
RAM
Currently running programs,
currently used data
ROM
Startup instructions
Issues
Volatile vs non-volatile
Size
Memory
Topic
Key Points
Cache
Buffer, small, quick
RAM
Main memory
Virtual Memory
Hard drive, large, slooow
Device Types
Topic
Key Points
Input
Keyboard, Mouse, Webcam, Mic
Output
Speaker, Monitor, Printer
Storage
Magnetic, Optical, Solid State
Processing
CPU
Communication
Modem, Router
Storage Devices
Topic
Key Points
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
Topic
Key Points
Security
Antivirus, spyware, firewalls
Disk organisation Defragmentation, formatting, FTP
System
Maintenance
System cleanup, automatic
updates, system info
Application Software
Issue 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
Topic
Key Points
How it works
Lookup table of values
Character Sets
ASCII, Unicode
Bits per character
Add 1 bit, DOUBLE the range
Representing Images
Topic
Key Points
How it works
Pixel colours in binary
Metadata
Height, width, resolution, colour
depth
File size
Resolution - Pixel density
Colour depth - bits per pixel
Representing Sound
Topic
Key Points
How it works
Sound samples in binary
Sample Rate
Frequency of samples,
Equivalent to resolution
Bit Depth
Bits per sample,
Equivalent to colour depth
Representing
Instructions
Topic
Key Points
Machine Code
Numeric values for instructions
Opcodes
Code for the Operation
e.g. add, store, load, branch
Operand
Address to be operated on
e.g. #0060
DBMS
Topic
Key Points
Database
Persistent, organised store of data
DBMS
Database Management System
Separates the program from the
data
Purpose
Create, maintain and interrogate
DB
Database
Components
Topic
Key Points
Tables
Entities, store of data
Forms
Interface for the table, easy to use,
view/add/edit records
Queries
Search / interrogate data
Reports
Organised layout, snapshot of the
data
Relational Databases
Topic
Key Points
Primary Key
Unique for each record
Foreign Key
Links to another table
Data
Redundancy
Avoid duplicating data
Only update one record
Networks
Topic
Key Points
Standalone
Not networked
LAN
WAN
Local Area Network
One Site
Bespoke Cabling
Wide Area Network
Separate Sites
Uses Telecomms Infrastructure
Network Hardware
Topic
Key Points
Network Card
Wired, wireless, bluetooth
Modem
Connect digital and analogue
Hub / Router
Communicate between computers
Wifi
Router, built in, dongle
Topologies
Topic
Pros
Cons
Ring
Few cables
Easy to break
Bus
Individual machines
won’t break network
Central bus can
break network
Star
Most reliable
Lots of cabling
Network Terms
Topic
Key Points
IP Address
Address for each machine
e.g. 192.168.0.101
MAC Address
Permanent address for each
device
e.g. ethernet, wifi and bluetooth
Packets
Split data into small parts to send.
Why?
DNS
Lookup table.
google.com => 217.143.12.98
Network Security
Topic
Key Points
User Access
Levels
Installing software, accessing key
files
Password
Policies
Avoid obvious passwords,
change regularly?
Encryption
HTTP vs HTTPS
Filtering
Blocked websites
Network Policies
Topic
Key Points
Acceptable Use
You signed one!
Disaster
Recovery
Keeping the business going
Failover
Redundant servers
Backup
Onsite, offsite, batch, sequential...
Webpages
Topic
Key Points
HTML
Rendering in web browsers,
<tags>, consistent standard
Filetypes
JPG, GIF, MPG, MP3, PDF
Lossless
Compression
Identical when recreating the file
Small size saving
Lossy
Compression
Some data - and quality - lost
Significantly smaller
Programming Terms
Topic
Key Points
Sequence
List of instructions in order
Selection
If statement
Iteration
While loop, For loop
Variables
Name, Type, Value
Data Types
Topic
Key Points
Char & String
Text
Integer
Whole Number
Real or Float
Decimal Number
(Decimal Fraction)
Boolean
True or False
Programming
Languages
Topic
Example
Key Points
High
Level
if score > 200:
print(“You win!”)
Cross-platform
Easier to read/write
Assembly
Hardware specific
LDA 36
Languag
Easier to read/write
Opcode & Operand
e
*than machine code*
Hardware specific
Machine
0110 0110
What the
Code
Opcode & Operand
processor uses
Translators
Topic
Compiler
Interpreter
Assembler
Key Points
From High Level to Machine Code
Batch job - find all syntax errors
Quicker to run once compiled
From High Level to Machine Code
Step-by-step - Stop at first error
Quicker to edit and test
From Assembler to Machine Code
One-to-one translation
Testing
Topic
Key Points
Strategies
Test the boundaries
Valid, Invalid, Extreme
Syntax Error
Mis-typed
Won’t run
Logic Error
Valid syntax - it runs
Doesn’t do what you intended