learn.dev42.co.uk

Computer Systems and Databases:

A computer system consists of hardware and software that work together to process data or complete tasks.

• Hardware - the physical stuff that make up your computer

• Software - the programs that a computer runs, you can have;

  • Application Software - programs that help the user complete specific tasks e.g. word processors, web browsers, databases, software, games etc.
  • System Software - designed to run and maintain a computer system e.g. OS, utilities etc.

General Purpose Computers:

• Definition - designed to perform many tasks and functions
• Examples - PCs, tablets, phones
• Advantages - can perform a wide variety of tasks, more affordable for multiple uses, and they can be upgraded for new changes/needs by being upgraded with new hardware/software

Embedded Systems:

• Definition - dedicated computers built into other devices to monitor and control machinery by being used as control systems
• Examples - dishwashers, microwaves, TVs
• Advantages - since they are dedicated, they are easier to design, cheaper to produce, and more efficient that general purpose computers

• Power Supply - supplies power to motherboard, optical drives, hard drives and other hardware
• Case Cooling Fan - extracts hot air from the computer case
• CPU Heatsink and Cooling Fan - keeps CPU at a steady temperature
• CPU - (hidden under the heat sink), the most important components as it does all the processing
• Optical Drive - for read/writing of optical disks
• RAM sticks - computer memory slots in here
• Motherboard - the main circuit board in the computer where the hardware is connected
• Hard Disk Drive - internal secondary storage
• Graphics Card - handles graphics and image processing

The CPU:

This is the brain of the computer as it processes all of the data and instructions that make the system work. Von Neumann architecture describes the main components of the CPU and how they interact with one another. A key feature is that it only uses one memory for both the data and the instructions.

The Control Unit (CU):

• Overall control of CPU
• Performs Fetch-Decode-Execute cycle
  • Fetch - The CU reads the memory address of an instruction and the instruction stored with that address is copied from memory to the registers
  • Decode - The instruction copied from memory is then decoded in the CU and the CU then prepares for the next step
  • Execute - The instruction is performed (write data to memory/ do a caluculation using ALU/ halt a program etc.)
• Controls flow of data inside the CPU (to other components; registers, ALU, cache) and outside CPU (to main memory and I/O devices)
• Keeps track of memory addresses of instructions for each cycle

The Algrothmic Logic Unit (ALU):

• Does all the collections
• Performs algorithmic instructions - addition, subtraction, multiplication, division and comparisons
• Performs logic instructions - AND, OR, NOT, XOR etc.
• Registers hold the intermediate results of calculations

Cache:

• Very fast memory in the CPU (faster than RAM but slower than registers)
• Stores regularly used data so CPU can access it quickly
• When CPU requests data, first checks cache; if not there then goes to RAM

• Low capacity and expensive in comparison to RAM and secondary storage

• A larger cache means the CPU has faster access to a larger amount of data it needs to process

The Clock:

• Sends out a signal that continually cycles between 1 and 0, usually at a constant rate
• Signal used to synchronise when instructions are carried out and helps coordinate flow of data

• clock speed is number of clock cycles per second

• A typical desktop computer has a clock speed of around 3.5 GHz (3.5 billion clock cycles per second)
• The higher the clock speed, the more instructions that can be carried out in one second

Buses:

• Collection of wires used to transmit data between components of the CPU and the CPU system
• A processor may have seperate buses for carrying data, instructions and memory addresses

Registers:

• Super quick memory to write into
• They temporarily hold tiny bits of data (data instructions and memory addresses) needed by the CPU
• There are specific registers for different tasks

Cores:

• Each core can process an instruction independantly to the rest
• More cores means more instructions can be processed at any one time

Memory:

Random Access Memory (RAM):

• main memory in a computer
• can be read and written into
• volatile - memory is temporary and if power is lost, any data is also lost
• all data, files and programs are stored here when in use
• software applications, documents and files are copied from secondary storage to RAM when in use
• slower than cache and registers but faster than secondary storage

Read Only Memory (ROM):

• non-volatile memory
• can only be read, not written into
• contains BIOS - instructions to boot up the computer

Secondary Storage: