Computer Systems

Computer systems (definition)

Combination of connected parts working together

Software (box)

Runs on box, monitor shows what's happening in the box

Operating systems

the low-level software that supports a computer's basic functions. E.g. Android, Windows 11

Hardware

Anything physically touched

Software

Anything that causes something to run

Browser example

Chrome

CPU instruction transmission

Instructions to open program sent to CPU. Hard drive loads program onto RAM. CPU ready to work

What does CPU stand for?

Central Processing Unit

CPU (location, basic info)

Known as Brain/processor. Located on Motherboard. Computer systems can't function without one as they're needed to process data

Functions of CPU

Carrying out calculations. Performing logical operations on data. Coordinating hardware (keyboard, mouse) taking in inputs, processing them, producing outputs.

CPU (job)

Searching. Sorting. Calculating. Decision-making. First two functions are "processing"

Control Unit

Controls signals needed to coordinate the running of the CPU and data movement

The ALU (Arithmetic Logic Unit)

Responsible for calculations and decision making of the CPU

Registers

CPU's memory store. Quick, temporary and expensive

Buses

Collection of wires which allow data/instructions to travel between devices

Data Bus

Moves data between CPU and main memory

Address Bus

Responsible for communicating memory locations that need to be fetched

Control Bus

Responsible for communication signals from the Control Unit. E.g. clock signal used to synchronise processes

Fetch (CPU Structure)

Address bus used to find location. Data retrieved by CPU via data bus + stored in Register

Decode (CPU Structure)

Control Unit receives instructions and decodes/ makes sense of them

Execute (CPU Structure)

ALU will perform the correct calculation. Control Unit uses address bus to find a memory location to store output. Control Unit sends data via data bus

Name the characteristics of a CPU

Clock speed, primary/secondary storage, cores, pipelining

Clock speed

Clock speed (amount of instructions that the CPU can process in a sec). Measured in Hertz (cycles per sec). CPUs run at approx 3 Gigahertz (3 bil cycles per sec).

Clock

Faster clock speed = more instructions can be processed. Speed of F-D-E cycle determined by clock chip. Chip uses vibrating crystal

Primary storage examples

Cache, RAM (Main Memory) (Random Access Memory), ROM (read only memory)

Secondary Storage examples

Hard disk/drive, Flash drive

Primary Storage features

volatile (temporary). Expensive + smaller, smaller in capacity, closer to CPU or integrated in it therefore faster

Secondary Storage features

Non-volatile (permanent), cheaper + larger, bigger in capacity, connects to CPU via cables therefore slower

Speeds of data transfer (fastest to slowest)

CPU register, Cache, RAM, Storage Device Types e.g. Hard drive, Input sources e.g. keyboard

Cache

CPUs can only work when given data. RAM cannot work at the same speed. Cache memory copies instruction needed at the the time and the following instructions

Cache (Speed + CPU)

Cache has a similar speed to CPU and is faster than RAM. To improve efficiency the Control Unit will first look in the cache to see if data is already copied. Larger cache = higher likelihood that the next instruction has already been copied

CPU Cores

CPU chips added to Processor to speed it up, known as cores. Each core carries out their own F-D-E cycles, multiple cycles carried out at once

Parallel Processing

Same program and its instructions get processed by multiple CPU cores (split work between them)

Multi tasking

Each core can process two different programs' instructions at once

CPU Cores (limitation)

More cores = more instructions processed at once. Doesn't mean the CPUs work faster, some programs don't allow more than one instruction to be processed at once

Pipelining

When the output of one stage is the input for the next. Pipelining used to speed up tasks carried out.

Pipelining (Limitation)

Only works if the CPU knows what instruction is to be fetched next. If failure of forecasting the next instruction and fetches the wrong instruction, pipeline flushed (cancelled)

Draw simplified Von Neumann architecture in sketchbook app

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Draw complicated Von Neumann architecture in sketchbook app

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What does the CPU consist of?

ALU. Control Unit. Registers. Heat sink. Program Counter

Function of heat sink

Remove excess heat from CPU

How does the heat sink cool?

Gaps allow air to pass through

What are the two types of hard drives?

SSD. HDD

What does SSD stand for?

Solid State Disks

What does HDD stand for?

Hard Disk Drive

What is an SSD?

Storage device based on flash memory, it has no moving parts and is faster and more durable

What is an HDD?

Storage with a spinning disk and a head that reads data. Slower and more fragile

Benefit of a HDD

Holds more storage than an SSD

Disadvantage of a HDD

More fragile and slower than an SSD

Benefit of an SSD

Less fragile and faster than a HDD

Disadvantage of a SSD

Less storage

Function of the power supply unit

Converts mains electricity into usable voltage

What does the power supply unit contain?

Fan to prevent overheating

Program counter (Function)

Holds the memory address of the next instruction. Memory address placed on address bus and RAM sends back the data at that address

Differences between RAM and ROM (RAM) (4)

RAM is volatile. RAM is faster than ROM. RAM is more expensive than ROM. RAM is removable from the motherboard. CPU can easily access data from RAM

Differences between RAM and ROM (ROM) (4)

ROM is non-volatile. ROM is slower than RAM. ROM is less expensive than RAM. ROM is removable from the motherboard. CPU cannot easily access data from ROM.

Processor speed (Definition)

The speed at which the fetch-decode-execute cycle happens

What is the accumulator?

A type of register

Accumulator (Definition)

Accumulator stores data to be operated on

Where is the Program counter found?

Control Unit

Where is the accumulator found?

ALU

What is virtual memory?

Type of secondary storage that stores data from RAM temporarily when RAM is full.

Disadvantage of virtual memory

Data here takes longer to be processed as it is no longer in RAM

Differences between RAM and Registers (2)

Registers are faster than RAM. Registers have a smaller storage capacity than RAM

What do transistors represent?

1s and 0s

Why may Moore’s law not be accurate in the future?

Physical limit as to how many transistors can be placed on an integrated circuit

What is Moore’s law?

Number of transistors on an integrated circuit will approx double every 2 years

What is ransomware?

Malware that threatens/blocks data by encrypting it until a ransom fee is paid within a time limit

How does RAM improve a computer’s performance?

More applications loaded onto RAM at the same time therefore less time spent loading data from secondary storage to RAM

What is hardware?

Physical component of a computer system- computer components e.g. RAM

What is software?

Programs that are executed by the processor e.g. Google Classroom and Microsoft Word

Difference between analogue and digital inputs

Digital has 2 discrete values represented by voltages in an electrical circuit. Analogue has any value within a range and represents continuous data