System architecture, memory and storage

The CPU (central processing unit)

Basic computer system model

Hardware - a physical component that makes up the computer

Software - a program that runs off the computer

A computer is made up of hardware and software

All computer must have a CPU and at least one input that gets data from the real world

Input devices tale real-world data and convert it into a form that can be stored on the computer, the input from these devices is processed and the computer system will generate outputs.

The output could be a computer screen.  

The fourth component is the storage. The computer system may need to use stored data to perform the processing and as a result of processing input, may generate data that is then stored. Any computer will have these processes.

Purpose of the CPU

to execute programs and manage the rest of the hardware.

Von Neumann architecture the concept of holding programs in memory and data would then be moved between the memory unit and the processor.

Components of the processor

The processor responds go sn processes the instructions that drive the computer. It contains the Cu (control unit), the ALU (arithmetic logic unit) and registers.

The accumulator is a special-purpose, very fast memory location in which all operations are carried out.

The programs instructions and data moe between  the main memory and the processor using internal connections called buses 

Three types of buses

• address bus - carries address from the processor to memory and input/output devices
• data bus - sends data between the processor, memory and input/output devices
• control bus - carries signals coordinate all the computer activity.

Control unit

Coordinates all the activities taking place inside the CPU. 

• It controls the execution of instructions in the correct order
• it decodes instructions
• it regulates and controls processor timing using regular pulses from the system clock  
• It sends and receives control signals to and from other devices within the computer

Arithmetic and Logic Unit (ALU)

• Logical operations: These include AND, OR  and NOT
• shift operations: the bit in a computer word can be shifted left or right by a certain number of places
• Arithmetic operations: these include addition, subtraction, multiplication and division. 

Special-purpose registers

very fast memory located within the CPU used to execute instructions.

A CPU has a number of special-purpose registers  

• Memory address register (MAR) - holds the address of the instruction
• memory data register (MDR) - temporarily hold the data
• a program counter (PC) - holds the memory address of the next instruction to be processes
• current instruction register (CIR) - holds the current instruction to be executed, which has been fetched from memory
• Accumulator (ACC) - the place that all the calculations are carried out in.

Function and characteristic of CPU

Fetch execute cycle

When a program is being run (executed) on a computer it first has to be loaded into the main memory. From here it can be accessed by the processor…