Computing Concepts

Units of Size Memory and Data rate

In computing memory is stored as a series of on off switches, units of memory divide memory up into manageable chunks.

Unfortunately due to the fact that computing is a relatively new subject abstract from other areas of science and the fact that most computer scientists have a tendency to believe "if it ain't broke, don't fix it" computing standards are somewhat complex.

The base unit, the bit (a portmanteau word for binary digit) is relatively simple and consists of a single on or off usually referred to as 1 or 0. Unfortunately here is where the simplicity ends as the correct unit symbol to use is somewhat debated with common computer use putting it as "b" but b is accepted by SI (International System of Units) as being a barn unit and the IEC (International Electrotechnical Commission) recommends using "bit".

As we move up the scale of size the controversy escalates. The Byte is nowadays used to refer to eight bits but originally referred to a number of different data chunks (such as 4bit or 16bit). The unit symbol for byte is generally B but SI recognise B as being bel (a measure originally use by Bell Telephone Laboratory but now more recognised as the bel in decibel dB), also French speaking countries sometimes use the capital letter O (for octet) but this causes confusion due to it's similarity to 0.

For kilobyte the confusion is even worse as it generally means 2¹⁰ or 1024 bytes but it can refer to 10³ or 1000 bytes. As another problem again the standard unit symbol is at odds with SI.

In practice the 2^X family of measurements is used when referring to memory storage but when talking about bitrate the 10^X family of measurements is generally used. Therefore if you see a memory stick labelled as 1GB it is 1073741824 or 2³⁰ bytes but in data rate (a subject we will touch on again in codecs) a kilobyte is 1000 or 10³ bytes.

Also according to EU directives non SI mesures will no longer be able to be used on advertising and packaging by 2009.

Somewhat confusing ne?

Cabling

In practise computer cabling is somewhat simplistic with modern cables reasonably distinguishable from each other. It is unlikely that you will come across serial cable and it would only be on older printers that you would find parallel cable. You may find yourself using SCSI if you are using older systems but again this is unlikely. You are much more likely to find your self using USB or Firewire for attaching peripherals and in the case of networking you are much more lightly to be using Cat5 UTP cable than Coaxial cable.

Expansion cards

The standard expiation slots you are likely to encounter on a computer are either PCI or in the case of graphics AGP. It is unlikely but if you are working with older computers you may encounter ISA slots. Common cards are NIC (AKA network cards) Graphics cards Soundcards and Additional ports. Also in many computers rather than relying on expansion cards these functions are built into the motherboard.

Forms of Memory

Or as a rather over zealous American customs officer who bore resemblance to Christopher Lloyd on steroids once put it when trying to test my claims to be a computing student "what's ram?" Now as much as I wanted to deliver a witty comeback I thought it would be detrimental to my chances of entering the country so I had to settle with a scathing look and the answer "Random Access Memory". And although this did go someway to satisfying our American friend (that and his failure to find the al-Qaeda hiding in my luggage) it lacks a certain je ne sais quoi when it comes to explaining what ram is and how it differs from other memory

RAM can be thought of as "thinking" memory rather than "remembering" memory. RAM is used by the CPU to store all the data and instructions it needs to carry out tasks, it can be seen as a giant set of pigeon holes above the desk of some one who is working. On occasion the person may need to swap some of the documents in the pigeon holes for files from the archive. This is what happens when the CPU pulls information from the hard drive onto ram to work on it.

RAM differs from hard disk memory in a few vital ways. Firstly its capacity is much lower but its access time is far faster. This is important because it allows the CPU rapid access to data. Also RAM is volatile, which means that if power is lost data will not be retained. Traditionally there are two types of RAM, Static RAM constructed from flip flops and Dynamic RAM constructed from capacitors, however you are unlikely to come across any Static RAM as Dynamic RAM is both cheaper and has more capacity than Static RAM although it is inferior in other ways.

We will cover ROM briefly in the section covering booting-up

What is screen resolution?

The resolution of your screen is the number of pixels you say your screen should attempt to display. In most cases this will not be related to the actual physical number of pixels in your screen but used more to set the size of your work area. As an example of this my current screen resolution on my main computer is 1600 x 1200 I use this resolution due to the large amount of workspace it gives me and the ability to work with extremely large images.

What is a driver (or extension)?

In computing in addition to the central hardware used to run the computer we often use additional pieces of hardware. It would be impossible to make every OS capable of running every single device out of the box simple because of the number of possible devices and the fact any new modifications would render the OS obsolete. Instead what happens is that all hardware that needs to be controlled by a computer either uses a standard interface or it comes with a set of instructions that allow the OS to communicate with the device, these instructions are called a device driver or an extension.

What are the ISO naming conventions?

The ISO (International Organization for Standardization) are a body that sets rules for a large number of commercial and industrial standards. They work closely with the IEC to set many computing standards. In this case we are interested in the ISO 9660 which sets the standard for CD file systems, I won't go into the details here except to say they are used industry wide for CDs but mostly with extensions such as Joliet for windows, El Torito for some boot disks and Apples own ISO 9660 extension that's supports HFS, fortunately these systems are backwards compatible so the other systems can still read the ISO data. Another note to take is if you use a rewritable CD it may well use UDF (Universal Disk Format - ISO/IEC 13346) which itself has an update in the works the Mount Rainier files system which is already supported in some Linux distributions and will be supported natively in Windows Vista (Longhorn)

The Internet and the World Wide Web

Often you will see people using the term "internet" and "world wide web" interchangeably but this is somewhat incorrect. The internet is the physical interconnected computer networks whereas the World Wide Web is the information stored on theses networks. To clarify the computer networks running on IP are the internet while the HTML HTTP and URI are the World Wide Web. If this seems confusing consider the case of e-mail. You may well use an e-mail client such as outlook or thunderbird and when you receive email you have used the internet while not using the World Wide Web. The World Wide Web is accessed from your computer by the use of an internet browser such as Firefox IE or Safari, these browsers use the internet to access and interpret the World Wide Web. Also using a series of browser plug-ins the browser can access and interpret additional information available on the internet. Common Browser plug-ins include Flash, Quicktime browser plug-in and Adobe Acrobat plug-in.

What are caching and buffering?

Caching is where small amounts of memory are used to store data that will be repetitively accessed to save time. It is also used as a fast access storage point for data when access time is an issue, for example there is often small ultra fast cache memory sitting between the CPU and RAM to improve performance.

Buffering involves a section of temporary memory being used to store data when the speed at which it is required is great than the speed at which is being delivered. This means that a portion of data can be stored so that when the buffer reaches a set point the data can be accessed at a steady rate until all the information has been received.