Comp 1

Comp 1

1. 1.1 Architecture

   • What is a computer system?
   • The purpose and components of the CPU
     • The clock is a tiny quartz crystal inside the CPU chip that 'ticks' at a steady speed.The CPU can only do something when the clock ticks. In-between each tick it does nothing. During each 'tick' the CPU can process a single instruction. However, the clock ticks extremely fast so you will not notice the delays in between each tick.
     • Located on the motherboard
       • A cache is a small, but extremely fast, type of RAM. It is often located inside the CPU chip itself.Data and programs currently in use are stored in RAM. But RAM is comparatively slow to access when compared to the speed at which the registers work. So to help speed up the processing time, cache memory is used to store instructions or data that are either frequently used, have recently been used or are about to be used. This means that they don't have to be fetched directly from RAM.
   • Von Neumann architecture
     • In the early days of computing (1940s), computers were built to carry out a very specific task. But if the computer then had to do another job, it literally had to be completely re-wired by hand.
       • Memory Data Register: In order for the CPU to fetch an instruction from main memory (RAM), the instruction is temporarily stored in a special register called the Memory Data Register (MDR). Data (unlike instructions) goes both ways. Data can be fetched from main memory and brought to the CPU to be processed. After processing, it may be sent back to RAM to be stored (short term). All data must pass through the MDR whether it is on its way to the CPU or RAM. All data and instructions pass via the data bus.
       • Memory Address Register: Every instruction or data in main memory (RAM) is located at a specific location. This location has a unique address, just like a house has its own unique address. The address of the data or instruction being accessed is temporarily stored in the Memory Address Register. This address is passed to RAM by means of the address bus.
     • with the Von Neumann architecture, both data and programs, whilst in use, are located in main memory (RAM).
     • Program Counter All data and instructions in memory have a unique and specific address. As each instruction is processed, the software that is currently running, updates the program counter with the address of the next instruction to fetch. The program counter then passes this next address to the memory address register as part of the standard fetch/decode/execute cycle (which will be explained in the next mini-web)
       • The Accumulator is used to temporarily store data whilst calculations are being performed within the Arithmetic Logic Unit (ALU) You need at least one accumulator register to carry out calculations.

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