Computer Systems Organization

 

A digital computer is a digital machine that solves problems with the instruction given by people or other machines. Programs are sequences of instructions describing how to perform specific tasks. Machine Language is the Computer's Primitive Instructure. Translation is converting a program from one level to another before execution. Interpreters are systems which execute instructions in another language directly by taking them as input data. Virtual machine emulates all the privileged facilities of a real machine so that a program appears to be executing with all machine facilities when in fact it is not. 

Most of today's modern computers can be described as multilevel machines from a high level language such as Java/C/Pascal to levels of actual machine to finally the results. The divice level contains basic elements for digital circuits such as transistors, diodes, and resistors. The logic level is a level with components called gates, denoted by "0" and "1". The microprogramming level is the true machine language and the programs used by this level are called microprograms. Every instruction in the conventional machine level has every instruction that can be a program in the microprogramming level. Operating system machine levels can be interpreted both by the operating system and the microprogram. A method for writing program for levels 1, 2, 3. Hardware consists of the electronic circuits, software consists of algorithms and firmware is the software embedded in the electronic devices when manufacturing. Assembly level and high level programming languages comes after machine level instructions. 

A fundamental concept in Computer Organization is a process state, which contains the program, an indication of what instruction to execute next, the value of all program variables, and the status/position of input/output devices. A state vector is a changeable part of the process. The 2 important properties of a process is that the affect of a process on execution speed, and the accuracy of a process. Given it runs over and over again, it yields the same results. 

The below will describe the execution of instructions on a computer.

First we want to fetch the next instruction from the main memory using the address from the PC and determine the type of instruction. If the instruction uses the data in the main memory, determine where they are if not determine where to go. Fetch data if any into the internal CPU registers and execute the instruction. Set the PC to the proper address value and repeat from step 1. So fetch data, execute, and update the PC instruction.