Systems Architecture

Control Unit (CU) - Controls all the other components of the CPU it contains the Decoder.

Decoder - Interprets program instructions and tells the ALU what operations to carry out.

Clock - Controls the rate at which program instructions are carried out, by sending control electrical signals at regular intervals, called Cycles.

Arithmetic logic Unit (ALU) - performs arithmetic and logical operations to carry out program instructions.

Buses - Electrical conductors that carry electrical signals between components in the CPU and between the CPU and other components on the motherboard.

Cache - Very fast random access memory (RAM)

Registers - Memory locations. Some perform special functions in the Fetch Decode Execute Cycle.

in 1945 John Von Neuman designed a stored program computer where both the program computer where both the program and data are stored in the memory. this is the design we use today.

The components are:

- a processing unit or CPU

- a program counter 

- memory to store data and instructions

- input and output mechanisms

Program Counter - holds the address of the next instruction to be fetched.

Memory data register (MDR) - a temporary store (buffer) for anything copied from memory

Memory address register (MAR) - holds the address of the memory location currently being read (fetched) or written to.

Accumulator - Stores the results of calculations carried out by the ALU.  

Fetch - Instructions and data are Transferred from the RAM to the CPU.

Decode - Control Unit interprets Instructions

Execute -  Control unit executes the instructions

The clock is a Vibrating Quartz crystal and the Faster it vibrates, the faster the instructions are processed.

the processor generates a lot of heat and the amount increases with the rate at which it processes instructions. the processor must have a Heat sink and a fan to dissipate this heat, liquid nitrogen is needed to cool supercomputers with clock speeds of 9GHz.

Cache memory is very fast memory, usualy in the processor itself. the cachespeeds up processing by storing recently or frequently used instructons so that they do not have to be fetched from the main memory which is much slower, as the cache becomes larger it takes longer to find the data and so it becomes slower 

cache is split into different levels eg. L1, L2 with the smallest nearest to the cpu. Cache memory is far too expensive to use for the main memory (RAM) in personal computers.

An embedded system is a computer system built into another device in order to control it.

Components in embedded systems are on a single printed circuit board (PCB), input devices may be manual switched and dials, such as on washing machies, the input device must convert changes ino electical signals.

Each embedded system is built for a small range of tasks

Embedded systems are called real time systems because they must ensure an immediate response to inputs.