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Representing Numbers
Recap on Binary Numbers
Binary digit (1 or 0)
­ known as a `bit', short for BInary digiT
­ bits generally grouped together in 8-bit bytes
­ a byte can hold 28 combinations of 0s and 1s
­ This means that, for example, 256 different
characters can be represented.
When `A' is pressed, 01000001 is sent to the
CPU.…read more

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Some of the ASCII codes
Char ASCII Char ASCII Char ASCII Char ASCII
space 0100000 8 0111000 P 1010000 h 1101000
! 0100001 9 0111001 Q 1010001 i 1101001
( 0101000 @ 1000000 X 1011000 p 1110000
) 0101001 A 1000001 Y 1011001 q 1110001
* 0101010 B 1000010 Z 1011010 r 1110010
+ 0101011 C 1000011 [ 1011011 s 1110011
, 0101100 D 1000100 \ 1011100 t 1110100
- 0101101 E 1000101 ] 1011101 u 1110101
.…read more

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Real Numbers
Numbers with a decimal point are known as
real numbers
The system for holding numbers in this way
is not part of the course.
Be aware that if `numbers' are to be used in
calculations, they have to be held as
numbers and not as text.…read more

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Digitised Sound
Sound can be input using a number of devices
As with basic telephone line, sound is analogue (wave form)
Convert to digital form (i.e. a binary pattern) for storage and
processing
Hardware ­ sound card does conversion from analogue to
digital and vice versa.
Sampling rate ­ how often the card takes a digital snapshot.
(higher ­ more accurate)
­ Measured in kHz ­ CD requires 44kHz (samples per second
Resolution ­ accuracy of measurement of amplitude of
sound.…read more

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Musical Instrument Digital Interface
MIDI is industry standard applied to:
­ Electronic musical instruments
­ Hardware, cables, connectors & data
MIDI interface allows computer to communicate:
­ Keyboards, drum pads, guitars etc.
MIDI data system stores all info. Necessary to synthesise
musical sounds.
Digitally stored data is very compact:
­ 30k for (1 minute of music)
­ Compared with 600k recorded
MIDI files on CDs or diskettes can be loaded and re-played
through sound card. Music can be altered because it is
stored as instructions.…read more

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Bit-Mapped Graphics
Screen is divided into a grid
­ Each square is called a pixel (picture element)
Higher Resolution has more squares
­ Standard used to be 640x480, is now 800x600 but rapidly
moving toward 1024x768 as standard
­ Monochrome only requires 1 bit in memory, (if 1, the pixel
is on, if 0 the pixel is off).
­ For colour, each pixel requires 1 byte in memory, giving
up to 256 colours for each pixel.…read more

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Bitmapped and Vector-based Graphics
Bitmapped images
­ are collections of pixels
­ Images created by setting colour and other attributes
for each pixel
­ the amount of memory required is dependent upon
the display adapter
­ Problems:
· May not look correct if transferred to another machine
with different adapter or resolution
· Distortion occurs when you try to enlarge the image…read more

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Bitmapped and Vector-based Graphics
Vector-based (or object-oriented) Graphics
­ Image is based on geometric data NOT graphic
data
­ A line defined by is endpoints, length, colour and
so on
· Used by CAD programs (or special graphics software)
to create the line on any screen regardless of its
resolution
· Thus, line-art of this type said to be device-
independent
· Can be re-sized without any distortion
­ Allows for much greater accuracy…read more

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