AQA Computer Science (paper 2) - Computer Systems & Computer Networks

What is computer hardware?

What is computer hardware?

Physical components of a computer system

What are the 2 main types of hardware

internal & external (aka. peripheral devices)

What is internal hardware? + examples

Physical components IN a computer system which help it process info.

Examples: CPU, RAM, motherboard, graphics card, HDD

What is external hardware? + examples

Physical components OUTSIDE or connected to a computer system.

Examples: keyboard, monitor, mouse, USB port, microphone

What is computer software?

Collection of programs, data and instructions that run on a computer

What are the two main types of software?

Systems & application software

What are system softwares & the two types of systems software?

= software that manages hardware & provides platform for application software

2 main types are: operating systems & utility software

What are operating systems & what are their functions?

= collection of programs that manage and control the computer.

Functions: MUMPS - memory management, user interface, multitasking, peripheral management, security!

List some examples of operating systems

iOS, android, windows

What is utility software? (+examples)

= software that helps maintain the computer system

eg. antivirus , encryption, data compression softwares

What is application software (aka. apps)? (+examples)

= software that performs end-user tasks

eg. word processors, web browsers, media players, CAD software

What is a device driver?

= a type of software which enables communication between the operating system and a hardware device

What are the 4 types of logic gates & how do they work?

1. AND Gate: Outputs 1 only if both inputs are 1; otherwise, it outputs 0.

2. OR Gate: Outputs 1 if at least one input is 1; outputs 0 only when all inputs are 0.

3. NOT Gate: Inverts the input; if the input is 1, the output is 0, and vice versa.

4. XOR (Exclusive OR) Gate: Outputs 1 if the inputs are different; outputs 0 if the inputs are the same.

What Boolean operators are used for each logic gate?

• . → AND gate

• + → OR gate

• ⊕ → XOR gate

• Overbar [line above letter] → NOT gate

What are the main difference between low-level and high-level programming languages? (2 points for each + examples)

Low-level (eg: machine code, assembly):

• Closer to machine code

• Less readable and more complex

High-level (eg: Python, Java):

• Closer to human language

• Easier to debug and maintain

What are the differences between machine code and assembly language?

Machine code:

• Consists of binary that the CPU directly executes (doesn’t need to be translated)

• Specific to a type of processor

Assembly code:

• Consists of mnemonics

• Needs an assembler to translate code to machine code (to be processed by CPU)

• Often used to make software for embedded systems

PS: Each assembly language instruction matches a machine code instruction exactly

What are 2 pros and 2 cons of low-level programming languages?

Pros:

• Faster execution

• More detailed control over hardware

Cons:

• Hard to read and write

• Less portable - specific to one processor

What are 2 pros and 2 cons of high-level programming languages?

Pros:

• Easier to read and write

• Have convenient features/libraries to improve development

Cons:

• Less control over hardware (compared to low-level)

• Slower code → abstraction & longer processing time

What is a translator?

Program that translates source code into machine code

What are the 3 types of program translators? (+outline how they work)

• Interpreters - translates code line-by-line

• Compiler - translates all the code in one go

• Assembler - translates assembly code to machine code

What are 2 pros and 2 cons of an interpreter?

Pros:

• Stops when it reaches an error- good for debugging

• Can run on many types of CPU

Cons:

• Slower than compilers

• Doesn’t produce a compiled file - re translates each time program runs

What are 2 pros and a con of a compiler?

Pros:

• Produces an executable program - don’t need to repeat process more than once

• Hides source code from end user - protects intellectual property

Cons:

• Compilation process is quite slow

What are 2 pros and a con of using assemblers?

Pros:

• Exact control over hardware

• Quick & efficient

Con:

• Less portable across different CPUs

What is the CPU + what does it do?

Component that processes data/ instructions and controls the computer system

What are the 5 main components of a central processing unit (CPU)?

• Arithmetic Logic Unit (ALU)

• Control Unit

• Clock

• Register

• Bus

What does the Arithmetic Logic Unit do?

= CPU component that performs the operations on the data

What does the Control Unit do?

= CPU component that control CPU activities

What are registers?

= quick & small stores of data within the CPU

What is a bus + what does it do?

= Collection of wires that data/signals are transmitted through from one component to another

What is the clock + what does it do?

= CPU component that provides timing signals to keep the CPU in sync

What is a network?

= 2+ devices connected together for communication purposes

What are 2 pros and 2 cons of having a network?

Pros:

1. File sharing across devices

2. Centralised management of security and updates across devices

Cons:

1. More vulnerable to viruses and hacking

2. Specialists needed for maintenance

What are the 3 types of computer network?

• Personal Area Network (PAN)

• Local Area Network (LAN)

• Wide Area Network (WAN)

What are the characteristics of a PAN?

• For close proximity devices (<10 metres)

• Bluetooth = most commonly used PAN

What are the characteristics of a LAN?

• Has small geographical area (under 1 mile)

• Managed by single person/company

What are the characteristics of a WAN?

• For wide geographical area (over 1 mile)

• Collection of LANs joined together, under collective ownership

• Internet = biggest WAN

What are 2 pros and 2 cons of wireless networks, compared to wired ones?

Pros:

• More portable as location is only limited by range

• Less expensive to setup & add devices

Cons:

• Slower data transfer than wired

• Less secure/safe than wired

What are the 3 most common LAN topologies?

• Star

• Bus

• Ring (not on spec)

What is a bus topology + how does it work?

= All devices are connected on a single ‘bus’ cable, terminated at each end (stops signal bouncing back)

• At each device: 1) Listens to electrical signals. 2) checking data packets for specific address. 3) Ignoring data packets it doesn’t recognise

What are 2 pros and 2 cons of a bus topology?

Pros:

• Easy and cheap to set up (only 1 cable is required)

• Doesn’t rely on any other network hardware (eg. Central hub)

Cons:

• Prone to data collisions

• If cable breaks, whole network is affected

What is a star topology?

= all devices are connected to a central switch/hub

What are 2 pros and 2 cons of a star topology?

Pros:

• Network can still work even if single cable stops working

• High speed + most efficient topology

Cons:

• If central switch stops working, entire topology fails

• High maintenance costs