1.1 SYSTEMS ARCHITECTURE

1.1 SYSTEMS ARCHITECTURE

1. A Computer System

   • HardWare
     • Computer hardware are the physical parts or components of a computer, such as the monitor, keyboard, computer data storage, graphic card, sound card and motherboard. By contrast, software is instructions that can be stored and ran by hardware.
   • SoftWare
     • Computer software, or simply software, is a part of a computer system that consists of data or computer instructions, in contrast to the physical hardware from which the system is built.
   • CPU
     • A central processing unit is the electronic circuitry within a computer that carries out the instructions of a computer program by performing the basic arithmetic, logical, control and input/output operations specified by the instructions.
   • Memory
     • Memory is the faculty of the mind by which information is encoded, stored, and retrieved. Memory is vital to experiences and related to limbic systems, it is the retention of information over time for the purpose of influencing future action.
   • GPU
     • A graphics processing unit is a specialized electronic circuit designed to rapidly manipulate and alter memory to accelerate the creation of images in a frame buffer intended for output to a display device.

2. Von Neumann Architecture

   • MAR
     • In a computer, the Memory Address Register (MAR) is the CPU register that either stores the memory address from which data will be fetched from the CPU, or the address to which data will be sent and stored. In other words, MAR holds the memory location of data that needs to be accessed.
   • MDR
     • A memory buffer register (MBR) or memory data register (MDR) is the register in a computer's processor, or central processing unit, CPU, that stores the data being transferred to and from the immediate access storage. ... The MDR is a two-way register.
   • PC
     • A program counter is a register in a computer processor that contains the address (location) of the instruction being executed at the current time. As each instruction gets fetched, the program counter increases its stored value by 1. ... Within a computer, an address is a specific location in memory or storage.
   • Accumulator
     • In a computer's central processing unit (CPU), an accumulator is a register in which intermediate arithmetic and logic results are stored.
   • ALU
     • An arithmetic logic unit (ALU) is a digital circuit used to perform arithmetic and logic operations. It represents the fundamental building block of the central processing unit (CPU) of a computer.
   • CU
     • The control unit (CU) is a component of a computer's central processing unit (CPU) that directs the operation of the processor. It tells the computer's memory, arithmetic/logic unit and input and output devices how to respond to a program's instructions. ... Most computer resources are managed by the CU.
   • Cache
     • Cache memory, lies in between CPU and the Main memory. It is also called CPU memory, that a computer microprocessor can access more quickly than it can access regular RAM. ... The basic purpose of cache memory is to store program instructions that are frequently re-referenced by software during operation.

3. Fetch Execute Cycle

   • An instruction cycle (also known as the fetch–decode–execute cycle or the fetch-execute cycle) is the basic operational process of a computer. It is the process by which a computer retrieves a program instruction from its memory, determines what actions the instruction dictates, and carries out those actions.
     • Fetch
       • The first step the CPU carries out is to fetch some data and instructions (program) from main memory then store them in its own internal temporary memory areas. These memory areas are called 'registers'. fetch decode execute cycle This is called the 'fetch' part of the cycle. For this to happen, the CPU makes use of a vital hardware path called the 'address bus'. The CPU places the address of the next item to be fetched on to the address bus. Data from this address then moves from main memory into the CPU by travelling along another hardware path called the 'data bus'. You could imagine that it is a bit like a boat attendant at a lake calling in customers when their time is up -- "Boat number 3, time to come in!" The 'address' of the boat is 3 and the 'data' is its content. The boat is parked at a pier, which is like the internal register of the CPU.
     • Decode
       • The next step is for the CPU to make sense of the instruction it has just fetched. This process is called 'decode'. The CPU is designed to understand a specific set of commands. These are called the 'instruction set' of the CPU. Each make of CPU has a different instruction set. The CPU decodes the instruction and prepares various areas within the chip in readiness of the next step.
     • Execute
       • This is the part of the cycle when data processing actually takes place. The instruction is carried out upon the data (executed). The result of this processing is stored in yet another register. Once the execute stage is complete, the CPU sets itself up to begin another cycle once more.

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