Hardware used in Multimedia Systems

Hardware demands on multimedia systems Multimedia puts huge demands on a computer system, so designers and users of multimedia systems need to have up-to-date technology including a high-res monitor, quality speakers, large primary memory, a fast processor and the latest in disk drives.

Hardware used Monitors/screens Projection devices Spekers CD ROM Video Head up displays

Monitors/Screens Monitors are a display surface that gives immediate feedback about what the computer is doing. Media forms it can display include…

CRT vs LCD

How CRT’s work CRTs receive their picture through an analogue cable and the signal is decoded by the display controller- like a mini-CPU for the monitor. At the back of a monitor is a cathode gun which fires electrons (cathode rays) towards the front through a vacuum which exists in the tube of the monitor. These rays correspond to to the red, green and blue channels of the display and video card. At the neck of the funnel-shaped monitor is an anode, which is magnetised according to instructions from the display controller. As electrons pass the anode, they are pulled or pushed depending on how magnetic the anode is at that time, moving the electrons to the correct part of the screen.

CRT’s continued… The electrons pass through a mesh which defines the individual pixels and resolution on the screen. Electrons that pass through the mesh then hit the phosphor coating which is on the inside of the glass screen. When the particles hit the phosphor, they immediately light up - causing the light to shine through the front of the monitor, making up the picture on the screen. There are three differently coloured phosphours for each pixel (known as phosphor triads), and depending on which phosphor the electron hits, that's which colour the pixel will light up.

CRT Shadow Mask Magnetic anodes Cathode ray gun Phosphor coated screen

CRTs and Refreshing Most CRT displays use a raster scan, which is where the electron stream is fired in a series of zigzag lines. This is repeated to maintain the image as the phosphor only glows for a moment. Interlaced monitors speed up refreshing by scanning the odd lines then even lines but this can cause the monitor to flicker. Non-interlaced can scan every line up to 72 times/second

Vector Display Systems A CRT screen designed specifically for vector graphics directs the electron stream to draw only the lines required for the image. Shading and tone can only be represented using a series of lines Vector Display systems have a faster refresh rate than CRTs using raster scans.

Liquid Crystal Displays LCDs are a flat screen consisting of a layer of liquid crystal material placed between two polarising sheets. Light passes through the liquid crystal, and at certain points a current is applied. LCDs are light, take up less space and power, produce no heat, have no glare and create no radiation.

Plasma Vs LCD What are some of the benefits and downfalls of each product? Plasma Vs LCD

Touch Screens Detect the touch of a person’s finger to enter and modify data. This works by light beams which form a matrix being interrupted when someone touches the screen surface. Touch screens do not allow for fine precision of input so therefore large buttons must be used.

Projection Devices A data projection panel is technology still sometimes used (especially as a teaching device). The projection panel is a LCD that is placed on top of a OHP to display the image from the computer. Data Projectors can take a video signal directly from a computer and project it onto a wall or screen. They are more versatile and smaller than a projection panel.

Head-up Displays uu

Head- up displays Head up displays are devices which can be worn on the head to display information. They were initially designed for military and gaming purposes but now have a far wider use.