2.1.2 Computing Hardware

2.1.2 Computing Hardware

1. The CPU (Central Processing Unit)

   • The CPU is the 'brain' of the computer. It controls all of the processes that the computer runs.
   • The CPU has two parts: the Control Unit and the ALU (Arithmetic Logic Unit).
     • The ALU performs arithmetic operations (multiplying, dividing, adding, subtracting) and logical operations (comparing two data items).
     • The Control Unit co-ordinates and controls all of the operations carried out by the computer.
       • Controls and monitors hardware attached to the system.
       • Controls input and output of data.
       • Controls the flow of data within the CPU.
   • The CPU operates by repeating the Fetch-Decode-Execute cycle.
     • Fetch: the CPU retrieves the instruction and any data involved from main memory.
       • Decode: the CPU decodes the instruction to make sure that it can be carried out.
         • Execute: the CPU carries out the instruction.
     • The program counter keeps track of the running order of the instructions and shows which instruction in the program is due to be executed next.
   • The CPU's performance is affected by the clock speed, cache size and the number of cores.
     • Clock speed, measured in hertz (Hz), is the number of instructions carried out each second.
     • Cache is a small amount of super fast memory in the CPU. Instructions fetched by the CPU are copied to the cache so that, if they are needed again, they can be fetched more quickly than having to go back to the main memory.
     • The number of cores is the number of duplicate CPUs on a single chip. This means several instructions can be run at the same time, so a quad core processor will be four times faster than a single core processor.

2. Memory