Unit 1.1 System Architecture version 3

Unit 1.1 System Architecture version 3

1. Processor

   • The CPU: Fetch ,execute , decode and process. It processes data and retrieves Data/Instructions from Main Memory which can be called fetch .It can also Stores Data into Main Memory once Executed.
     • Control Unit : Control the flow of data within the CPU (i.e. between registers), control input and output of data to/from the CPU, controls the timing of signals sent within the CPU.
     • ALU: Arithmetic & logic unit, used to perform arithmetic calculations (e.g. add, subtract, multiply), used to perform logical operations (e.g. <, >, =, !=).
   • Processor Speed
     • Measured in Hertz (Hz) Typical Speeds have spanned across MHz and GHz 1GHz Processor executes 1 Billion Instructions per second 2GHz Processor executes 2 Billion Instructions Per Second
       • Cache: Stores frequently used instructions and data, built onto the CPU, provides faster access than RAM, allows instructions and data to be loaded into the CPU more
       • Cores: With more cores instructions are carried out simultaneously, the processor can process more instructions at the same time, which allows batches of instructions to be executed more quickly, which allows for more programs to be run at the same time.
       • Clock Speed: With a higher clock speed the instructions carried out per second and so instructions are executed more quickly, which allows for more programs to be run at the same time. This then allows for more complex processing (e.g. 3D graphics) to be completed in real time.

2. Register:A component for holding short term memory, used to store addresses or data currently being worked on.

   • MAR: Memory Address Register used to store the address of the next instruction / data to be accessed
   • MDR: Memory Data Register, used to store the data to be brought from / sent to main memory Program Counter, used to store the address of the next instruction
   • PC – Program Counter Holds the location of the next instruction/data address in Main Memory

3. Main Memory

   • RAM-Random Access Memory: RAM holds data and instructions that are used by the processor .RAM is located in the motherboard and is directly accessible because of the processor .All data in RAM is lost if there is no power which is opposite to ROM. An example of a way to use RAM is by video games as when you turn your computer off it can no longer send instructions.
     • Secondary Storage: This is storage that is used for long term memory and data from I/O port e.g. Hard Disk Drive, Flash Memory, DVD and Blu-ray .
       • I/O Ports allow communication from an I/O device and the motherboard (hence CPU)
         • IO controllers:These are used to allow an interface between a hardware device external to the motherboard (e.g. a Keyboard) and the Processor itself. I/O controllers are used for: Keyboard, Mouse, Disk Drive, VDU
   • ROM – Read Only Memory: This is memory that is always on a device. This means data and instructions can still be sent even if the device is turned off. An example of ROM is Windows as it cannot be uninstalled in a traditional manner.
     • EEPROM – Electronically Erasable Programmable Read Only Memory: Instructions/Data can be erased electronically and replaced an example of this is Sim card or a flash drive.

4. Buses

   • System Busses: A bus is a set of parallel wires connecting multiple independent components of a computer system in order to pass signals between them. The system is split into three different busses the data bus, the address bus and the control bus.
     • Data Bus: Carries data or instructions from the main memory (or a secondary storage device) to the processor. The data bus is Bi-directional which means it can go both ways and the data transferred can be read and written on.
     • Address bus: The address bus carries addresses created for the processor to main memory or other I/O devices. The address bus is Unit-Directional which means it can only go in one direction. All instructions or data goes back on the Data Bus.
     • The Control bus: Control signals are sent along the control bus form the processor with other devices.