Computer Systems History & Architecture

System Flow Chart

Computers have been in the scene since the 16th century and they were mostly mechanical beings the size of a house. The competition and demand kick started in the late 19th century and all computers became electronic, programmable, powerful and smaller in size. Standards were developed and all modern day systems are designed on the same principle. The input and output devices are fed into the Arithmetic Logic Unit through the Accumulator. The ALU, control unit and the memory are all interconnected by multiple two way data buses. The functions are explained in details below.

Central Processing Unit

Laptop CPU

CPU is a computer brain it executes all program code instructions and controls the inputs and outputs of the system. The computer power is mainly the measure of how fast the CPU gets things done. Factors that determine processor power includes:

  • Clock Speed - In today’s CPUs is measured in GHz. These are on and off square waves generated by the quartz piezo electric oscillator and then fed to the clock generator for multiplying, inverting and monitoring to suit all types of applications. These waves also called clock signals are used to shift zeros and ones in and out of registers or in general terms to synchronise devices. Depending on the system i.e. synchronous or asynchronous, data will be shifted on the rising or falling edge of the clock signal. Therefore is clear that having more frequent waves means having more data shifted quickly hence the faster CPU.
  • Instruction Cycle - Instruction sets are in 8, 16, 32 and 64 bits for standard computers in today’s commercial computer market. Simple CPU instruction cycle can be divided into four segments Pre-fetch, Decoding, Memory operands and Execution. Therefore a 32bit microprocessor means it has the capability to process 32bits of data & instructions in 1 instruction cycle and 64bits on a go for 64bit CPU. Therefore a 64bit CPU will process more information than a 32bit one on the same clock frequency hence the higher the bits the more powerful the CPU.
  • L1, L2 Cache - To understand cache operations better let’s take a typical human situation in the office. If your desk is fitted with a smaller fridge drawer you will most likely put refreshments that you drink most when you are busy working therefore saving you time of going to the main stuff kitchen every time you are thirsty. That’s exactly what the CPU does with cache it stores copies of the most frequently accessed memory locations. If a memory read or write is requested the system checks L1 cache if not there it goes to L2 and if that is the same situation it heads to the main system memory which is equivalent of going to the kitchen. The L1 and L2 are fast inbuilt static memory ranging from 16KB to 4MB and main system dynamic memory is much slower and bigger up to 32GB in today’s computers. Which means if a CPU finds what it is looking for in the l1 & L2 then the whole operation will be much faster than fetching from the DDR memory. Therefore the bigger the L1 & L2 the quicker the CPU operates.
  • CPU Cores - In human concept they say two heads are better than one and that’s the exact implementation of multiple core CPUs. The demand for more computer power has gone over the roof and designers are pushed over the edge to deliver and they have gone as far as fitting up to 8 cores in one die unleashing WOW performances. Basically the more cores your system has the more powerful it is.