Computer Systems - Chp 6

System

a combination of many connected parts all working together to achieve a common goal

Computer system

can be described as one that involves the interaction between:

1. Hardware eg. physical computer

2. Software (a computer program)

3. Data

4. The (human) user

Neumann Architecture

Central processing unit
Memory
A bus
Input and Output devices

Central Processing Unit (CPU)

Which processes, carries out or executes instructions

Memory

Which stores both the data to be operated on, and the instructions (programs) that operate on that data and the results

Bus

Connecting the CPU and memory

Input and Output devices

That allow data to come into the computer and results to be sent out

ALU

Arithmetic Logic Unit, where arithmetic and logical processing takes place ALU receives instructions (from programs stored in memory) and data (stored in memory) and operates on the data according to these instructions.

Control Unit

Directs the operations of the CPU

Registers

Temporary storage locations (memory) that CPU can access quickly when carrying out operations on data. eg. of register is program counter

Program counter

stores and or keeps track of where the CPU is in the program sequence at any given time

RAM

Random Access Memory. temporary memory, holds the data and instructions of the program that are currently being executed by the CPU. Volatile memory.

ROM

Read Only Memory. Non volatile memory. eg. of ROM is BIOS (basic input/output system), small amount of ROM that is used to store the computer's start up routines. when computer is powered on BIOS completes the necessary checks and passes over control to the operating system.

Primary Storage

Memory that is used to store information for immediate use by the CPU is known as main memory or primary storage. eg. RAM and ROM

Fetch-Decode-Execute Cycle

• CPU fetches the program's next instruction from memory.

• Instruction is found at a memory address and stored in binary code.

• CPU decodes the binary code revealing an instruction which is executed.

The Clock

generates a signal consisting of a continuous stream of electric pulses at a very stable frequency. pulses fed to all circuits in the computer system to ensure that they operate together using exactly the right timing.

Factors determining CPU speed

1. Clock speed, each pulse = cpu fetches and executes 1 instruction

2. Cores, parts of cpu that can execute instructions simultaneously. eg. cpu has 8 cores = 8 instructions may be carried out during one clock cycle.

3. Cache system - size and speed of this can also affect performance greatly.

USB

Universal Serial Bus

Secondary Storage

Secondary storage devices are used to store data persistently. Non volatile

Electricity

A form of energy caused by the movement of electrons.

Electric current

The flow of electrons from one place to another is known as electric current. the greater the rate of electron flow, the greater the current there is.

Voltage

an electron experiences a force when there is a difference in charge between its current location and another location. This difference in charge is called voltage or potential difference.

Resistance

a measure of how much a material resists the flow of electric current.

Transistors

Small electronic switch. allows a smol current change to "switch" on or off a larger current

Resistors

A device that reduces current flow. done by passing electricity thru a material which has a resistance that allows electricity to flow but not efficiently

Capacitor

stores electrical energy in the form of electric charge. unlike batteries which also store electrical energy these dont store energy for long periods of time often used in volatile memory RAM.

Capacitance

measure of amount of charge a capacitor can store

World Wide Web

a system of connected files hosted on the internet. Can include pages, pictures, videos and other file formats that can be searched and browsed. all of these are connected using hyperlinks.

Internet

A global network connecting millions of computers, making it possible to exchange information.

Cloud Computing

refers to storing, processing and/or accessing data, programs or services over the internet on servers that are specifically designed for these purposes.

positives of cloud computing

• ability to share files easily between many users

• remote access to files

• always having access to the most up to date software

negatives of cloud computing

• risk of a security breach

• requirement to have an internet connection to access files