models

The Input Output Model

This model is used by Dr. Chuck, and is one way we can visualise a computer system. Computer peripherals can be categorised as input, output or storage, with the CPU doing the processing.

Input Output model of a computer system

The same model can be applied to applications, or going even smaller, to objects or functions.

An application such as MS Word takes input from the keyboard and mouse, and the output is displayed on the screen. Internally this may be cached (saved) with or without the user knowing.

This model is also used in designing and testing functions- the designer can specify a range of inputs and check if the function returns the expected output.

The Hierarchical Model

This view of a system views the hardware and software as a system composed of many parts. As in the figure shown here, the computer is made up of many parts. Many of these parts may then be broken into smaller parts and sub-systems. Some of these may further be broken into smaller parts. For example, many components are situated on the main-board or motherboard. Each of these components may then be broken into sub-parts.

The CPU is one component on the motherboard, and has within it many sub-units such as the Arithmetic Logic Unit (ALU), Control Unit (CU) and Memory. The memory can be broken into tree types- ROM, RAM and cache (registers).

The ALU is it self comprised of control logic, registers, and circuits to perform arithmetic and logic operations. These circuits are made up themselves of sub-circuits, which then are made with gates called XOR, AND and OR and so on. These gates are created from transistors. These transistors are made from a material which itself can be broken down to the molecular and sub-atomic level. It's hierarchies all the way from the sky down.

The main concept here is that everything is made up of other things- society, education, cars, animals, people.

the memory and input hierarchy

The memory hierarchy is useful. The fastest and most expensive memory sits at the top of the pyramid.

As we go down this particular hierarchy, memory typically gets larger in capacity, slower and cheaper.

Not all software is equal. What users experience for the most part is the application software- using Word, or a web browser.

This "sits" on top of an Operating system (OS).

The OS itself has sub-units that interact with lower levels right down to the hardware of the computer.

Without software, a computer is just an expensive paperweight.

In this course, we will learn more about the topics listed under development software.

the software hierarchy

A Platform

A platform is a combination of the hardware in a computer, and the Operating system. These two things combine to provide a platform, and it is on top of this platform that we can run applications. If you look up the minimum specifications for installing a new OS such as Ubuntu or Puppy Linux, these OS' specify a minumum hardware requirement.

When you look at particular applications such as games, or graphics/drawing packages, they will specify both the compatible Operating Systems AND the minumum hardware requirements to be able to run the package.

a platform is composed of the OS and the hardware

The VM stands for virtual machine. It was added to facilitate the following concept:

If your computer is running on Ubuntu Linux, can one run Microsoft Word? Strictly speaking, no- because MS Word will only run on MS Windows- it is platform dependent. BUT- there is software that acts like an adaptor, called a virtual machine. It sits between the application and the OS, and makes the application "think" it is working on it's preferred OS in the same way that you can use your "Ire/UK" plug in other countries- you have an adaptor between your charger and the socket.

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