Systems Architecture

Systems Architecture

1. General Purpose Computers

   • a computer that is designed to be able to carry out many different tasks.
     • PC
     • Phones
     • Computer
   • The CPU receives instructions and data from an input or memory. The instructions and data are processed by the CPU and the results are either sent to an output or transferred to secondary storage. Input is from an input device, such as a keyboard, mouse, camera or scanner. Output is to an output device, such as a monitor, printer or speaker.

2. Hardware and software

   • Hardware is the physical components of the computer
     • CPU
       • Central processing unit - the brain of the computer that processes program instructions.
       • The CPU is the most important hardware component in a computer. It has two main functions: to process data and instructions to control the rest of the computer system All programs and data processing are run in the CPU and all hardware components are, to some extent, controlled by it.
       • The central processing unit (CPU) consists of six main components:
         • control unit (CU)
           • The component of the CPU that manages instructions.
           • The CU provides several functions: it fetches, decodes and executes instructions it issues control signals that control hardware it moves data around the system
         • clock
           • A component of the CPU that sends out regular pulses. Its job is to synchronise the computer's hardware components.
             • The CPU contains a clock which is used to coordinate all of the computer's components. The clock sends out a regular electrical pulse which synchronises (keeps in time) all the components. The frequency of the pulses is known as the clock speed. Clock speed is measured in hertz. The higher the frequency, the more instructions can be performed in any given moment of time. In the 1980s, processors commonly ran at a rate of between 3 megahertz (MHz) to 5 MHz, which is 3 million to 5 million pulses or cycles per second. Today, processors commonly run at a rate of 3 gigahertz (GHz) to 5 GHz, which is 3 billion to 5 billion pulses or cycles per second.
         • arithmetic logic unit (ALU)
           • A component of the CPU that performs arithmetic and logic calculations.
           • The ALU has two main functions: It performs arithmetic and logical operations (decisions). The ALU is where calculations are done and where decisions are made. It acts as a gateway between primary memory and secondary storage . Data transferred between them passes through the ALU.
         • buses
           • A channel of communication used to transport data and instructions in the CPU.
             • A bus is a high-speed internal connection. Buses are used to send control signals and data between the processor and other components. Three types of bus are used: Address bus - carries memory addresses from the processor to other components such as primary memory and input/output devices. Data bus - carries the actual data between the processor and other components. Control bus - carries control signals from the processor to other components. The control bus also carries the clock's pulses.
         • cache
           • A piece of temporary memory. It can refer to a part of the RAM, storage disk, CPU, or an area for storing web pages.
             • Cache is a small amount of high-speed random access memory (RAM) built directly within the processor. It is used to temporarily hold data and instructions that the processor is likely to reuse. This allows for faster processing as the processor does not have to wait for the data and instructions to be fetched from the RAM.
         • registers
           • The section of high speed memory within the CPU that stores data to be processed.
             • Registers are small amounts of high-speed memory contained within the CPU. They are used by the processor to store small amounts of data that are needed during processing, such as: the address of the next instruction to be executed the current instruction being decoded the results of calculations Different processors have different numbers of registers for different purposes, but most have some, or all, of the following: program counter memory address register (MAR) memory data register (MDR) current instruction register (CIR) accumulator (ACC)
     • Hard disk drive
       • A device used to store large amounts of data.
     • Monitor
       • A screen that displays output from a computer.
   • Software is the programs that run on a computer.
     • Programs
       • Sequences of instructions for a computer.

3. Von Neumann Architecture

   • Von Neumann architecture is the design upon which many general purpose computers are based. The key elements of Von Neumann architecture are:
     • data and instructions are both stored as binary digits
     • instructions are fetched from memory one at a time and in order (serially)
     • data and instructions are both stored in primary memory
     • the processor decodes and executes an instruction, before cycling around to fetch the next instruction

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