Definitions
CPU (Central Processing Unit)
The key component of a computer system that fetches, decodes, and executes program instructions
ALU (Arithmetic Logic Unit)
Part of the CPU that performs all arithmetic and logical calculations
CU (Control Unit)
Component of the CPU that manages the loading and decoding of commands, directing data flow and ALU operations
Registers
Small, very fast circuits that store intermediate values from calculations or instructions inside the CPU
MAR (Memory Address Register)
A CPU register connected to the address bus, containing the memory address of the next instruction to be fetched
MDR
A CPU register connected to the data bus, holding data to be written to or read from RAM
Buses
Connecting wires that connect the CPU to other devices, carrying instructions to/from components.
Data Bus - Links RAM to CPU via MDR
Control Bus - Links RAM to CPU via CU
Memory Bus - Links RAM to CPU via MAR
Primary Memory
Fast storage directly accessible by the CPU, used for temporary data and instruction storage during processing
Secondary Memory
Non-volatile storage with higher capacity but slower access than primary memory, used for long-term data storage
RAM
Volatile primary memory used for temporary storage of data and instructions that the CPU needs quick access to
ROM
Non-volatile primary memory that retains information without power, used for storing critical firmware or permanent software e.g. BIOS
Cache
A type of small, high-speed memory inside the CPU is used to hold frequently used data, so the CPU needs to access the slower RAM less frequently
Operating System
System software that manages computer hardware, software resources, and provides common services for computer programs.
Application Software
Software designed for specific tasks or user applications, such as word processors or web browsers
Volatile
Loses content if power is lost
Non-Volatile
Does not lose content if power is lost
The basic operation of a computer is called the ‘fetch-execute’ cycle (also called the ‘machine cycle’). The computer fetches the instruction from its memory and then executes it. This is done repeatedly from when the computer is booted up to when it is shut down.
Step 1 – Fetching the instruction
The first step the fetch-execute cycle carries out is fetching the instruction. The CPU fetches this from the main memory (RAM) and stores it in the CPU temporary memory, called the registers.
Step 2 – Decoding the instruction
Once the instruction has been fetched, the CPU will need to understand the instruction to action it. This is called decoding.
Step 3 – Executing the instruction
When the instruction has been decoded, the CPU can carry out the action that is needed. This is called executing the instruction. The CPU is designed to understand a set of instructions - the instruction set.
Persistent storage is needed to store data and programs after the computer is turned off. Otherwise, all the programs and data would need reinstalled every time the computer is restarted. Also, RAM is limited in a computer while large amounts of secondary storage are relatively cheap.
Examples of Secondary Storage -
An operating system (OS) is a fundamental piece of software that manages a computer's hardware resources and provides essential services for other software applications. It acts as an intermediary between the computer hardware and the user.
Some of the main functions of an operating system include:
- Process management: The OS oversees the execution of programs, allocating CPU time and ensuring efficient multitasking
- Memory management: It allocates and manages the computer's memory, optimising usage to prevent crashes and ensure smooth operation
- File system management: The OS organises and controls file storage, creation, deletion, and access permissions
- Device management: It manages and controls various hardware components and peripherals, often using device drivers
- User interface provision: The OS provides a graphical user interface (GUI) or command-line interface (CLI) for user interaction
- Security management: It handles user authentication, access rights, and implements security measures like firewalls
- Resource allocation: The OS efficiently distributes system resources among different applications and processes
- Input/output operations: It manages data transfer between the computer and its input/output devices
What is application software?
Application Software is designed for the end user and is not needed for the running of the computer. It has specific tasks that are useful for the end-user.
Examples -
- Word Processor
- Spreadsheet
- Database Management System (DBMS)
- Email Clients
- Web Browser
- Computer Aided Design (CAD)
Please note that we do not use brand-specific application names. You will also need to know what each of these examples does.
Common Features:
Most programs will have the following features -
- Toolbars
- Menus
- Dialogue Boxes
- GUI Components
OS vs Application Features
Certain parts of the interface are provided by OS libraries, and certain parts are specific to each application.
