Category Archives: 1. Computer Systems

1. Computer Systems, FAQ, Revision

FAQ – Hub or Switch

Simple description  of the functions  and  uses of a hub, switch and router

  • Hub
    • A Hub is a multi-port repeater. That means that data coming into one port is sent out of all other ports. This can result in congestion on the network as machines are swamped with data that id not for them, resulting in a slow down of network performance. A 100Mbps hub shares this with all machines, so each machine only gets a fraction of the speed.
  • Switch
    • A switch keeps a database of each machine on the network and which port of the switch they are connected to. These collision domains are controlled by the switch, which then results in a reduction of the number of collisions increasing the overall speed of the network. A 100Mbps switch gives each machine 100Mbps.
  • Router
    • A router is a device with two network cards that is responsible for routing data from one network to another. It does this by keeping track of IP addresses of computers on the networks and forwarding packets appropriately.

Remember the warriors of the net video is a good lead in, but look up the terms online.

[kml_flashembed movie="http://www.youtube.com/v/PBWhzz_Gn10" width="425" height="344" allowfullscreen="true" fvars="fs=1" /]

1. Computer Systems, Computing Higher

Our new PCs

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Well I finished setting up the new machines today, and even as I type this, the network should have finished installing software on them and is shutting them down.

I took one of the machines out for a bit of a test to see what it could do, but before I comment on that, lets look at the specs.

  • i5-2400 processor
  • 4GB RAM
  • Windows XP 32bit
  • 512MB GPU (can’t remember the model right now except it was a radeon)

The machines are in a slimline case and look OK for a HP.  I loaded up most of the games that were too slow for my old machines; warsow, world of padman, etc. I set the graphics options to max and had a look at the frames per second – rock solid on 75+FPS, which means they should be fast enough for anything we want to do.

One thing though, the desktops are only reporting 3GB, why is that and what can we do about it?

1. Computer Systems, Computing Higher

Password Security

I found this image on the net and I would have endorsed it whole heartily in the past but my choice of passwords has changed recently.

(c) zonealarm

One of the reasons for making passwords cryptic was to stop the casual observer keyboard watching your password. Now though we tend to use our own machine so the need to protect against observers has lessened. However recent GPU based password crackers have rendered this method of password creation virtually obsolete, so we need a new way to remember passwords.

We are no longer limited to 8 character passwords (can you guess why the limit was 8?), so we could use a sentence. The chances are though, there will be password dictionary based on song lyrics or movie quotes along any day now and Artificial Intelligence might make a good stab at these in the future. So we need a way of remembering passwords that are strong and hard to brute force. I found this image that conveys this perfectly.

(c) XKCD.com

So the next time Facebook or Glow asks you to create a password, try and think outside the box.

REMEMBER attempting to access someone else’s account is illegal and a breach of the Computer misuse act in the UK. The Internet makes it easy to access computers around the world and some countries have more severe penalties.

1. Computer Systems, 3. Multimedia, Computing Higher

Number of colours

The Number of colours is calculated as using 2bit depth So we have the following. The phrase colour depth can be used in place of bit depth.

Colour Depth Number of Colours Description
1 2 Black and White
8 256 8bit
16 65,536 High Colour
24 16,777,216 True Colour

On a side note, I asked the maths department how to go from the number of colours to the colour depth.

Mr Barnstaple helpfully provided me with this

  • Colours = 2Bit Depth
  • Bit Depth=log(Colours)/log(2)

Which is I’m sure we will all agree very useful,  but it might be easier to memorise the table above 😉

PS if you want the proof  here it is Continue reading Number of colours →

1. Computer Systems, 3. Multimedia, Homework

Graphic file sizes calculations

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We covered this in class last week. Forrester have a good concise article on this subject

Please answer these questions

1. 600 x 300 pixels, 24 bit colour depth

2. 600 x 400, 16 bit colour depth

3. 600 x 600, 24 bit colour depth

4. An image is 6 inches by 8 inches, and has a resolution of 1200 dpi. It has a bit depth of 20.
(a) How many colours can the image store?
(b) What will be the file size of the image?

5. A photograph measures 10 inches by 7 inches, and has a resolution of 400 dpi. The number of colours each pixel can store is 65536.
(a) What is the bit depth of the image?
(b) What will be the file size of the image?