IGCSE Computer Science – CSC-IGCSE-07 –
Complete Revision Summary on Data
Representation, Transmission, Hardware,
Input/Output Devices & CPU Architecture
binary numbers are used in - computer systems
conversion from denary to binary and from binary to den - use place values
memory size of a computer is measured in terms of the number of - bytes
1 kilobyte is - 2 to the 10 bytes
1 megabyte is - 2 to 20 bytes
Or 1 kilobyte according to manufactures - 1000 bytes
Increase from - kilto to mega to giga to tera
unit symbols - kilobyte-kB
megabyte, gigabyte,tera byte is- CAPITAL thenB
Each increase by - 1000 so mega byte has a 1000 kilobytes so thus a 1000000 bytes and a giga byte
has a 1000 mByte
binary registers - group of bits in computer memory, each bit does something different so if 1 then x
does y, small piece of memory built into cpu, where values and instructions are temporarily held. Not
primary or secondary, very fast read and write rate, comp systems use registers to hold values and
instructions for processing to increase the speed at which they are processed
Why choose Hex - Quicker to read, easier/quicker to write in hex, less likely to make errors copying
so easier to debug Letters in Hex - A=10
B=11
C=12
D=13
E=14
F=15
Register - Temporary piece of storage, status = stores what happening for reading, control gives
instructions for writing
MAC addresses - media access control address 12-bit identification number unique for each device.
Unique number that identifies a device, manufacturer id and serial number of device, address is
allocated by manufacturer
,Defining colours in HTML - Uses hexadecimal when representing colours, combinations of hex codes
are used to represent different colours
#FF 00 00 = primary red
#00 FF 00 = primary green
#00 00 FF = primary blue
Memory Dumps - If there is an error in program it is useful to carry out memory dump, this is
contents of a section of computer memory, Contents of a number of memory location are outputted
in Hex format, Software engineer can then look at memory dump and find where error lies. Using
Hex makes it easier and faster because ^
Assembly language and machine code - Memory location can be addressed directly using assembly
language or machine code, this means its easier for programmers to write the code because not
using binary
sound, music, pictures, video, text and number are - stored in different formats
Musical instrument digital interface - MIDI file comprises of data stored as a list of messages telling
device how to generate a sound or music. Software saves the messages as .mid file, when played on
an electronic keyboard the keyboard's software follows the .mid fil instruction and produces music,
-doesn't contain actual music so file size is much smaller than MP3 or MP4 files, 1Mbyte file size to
store one minute under MP3 and 10kbyte Midi
MPEG-3 files - uses audio compression technology to convert audio to MP3 format, normal music on
cd is compressed by a factor of 10. Uses perceptual music shaping, which removes sounds the
human ear cannot hear properly, if 2 sounds are played MP3 discards softer sound that can't be
heardeg
MPEG-4 files - format which allows multimedia rather than just audio files. Work in similar way to
MP3 but they store audio , video, photo and animation files. Work b compressing files without
affecting the quality by making certain aspects of the file redundant
Jpeg files - image encoding system that compresses photographs and other images. Lossy format and
makes use of certain properties of human vision to eliminate certain unnecessary info
Lossless file compression - breaking down into files of similar size for transmission or storage and
then put back together again at receiving end so it can be used again
Lossy file compression - Lossy compression algorithm eliminates unnecessary bits of information. It
becomes impossible to get back to the original file once this lossy compression algorithm has been
applied and the new file stored.
Algorithm looks for redundancies in file and eliminates them to reduce file size
Lossy Compression mark scheme points - images contain less detail without noticeable degradation
in quality
streams faster than lossless compression
if 2 sounds played at the same time, softer sound is removed
, when decompressed some detail is lost and file is not exactly like the original
Lossless compression mark scheme points - original and decompressed file will be the same
for code, decompressed file and original file must be exactly the same otherwise file wouldn't work
after decompression original file is restored with no loss of data
Data Transmission - Transferring binary data from sender to receiver
Serial - Data transmitted one bit at a time over a single wire
Parallel - Data transmitted several bits at a time simultaneously over several wires.
Advantages of Parallel - Faster, works well over short
Advantages of Serial - Cheaper cabling, works well over long
Disadvantages of Parallel - Conductive wires close together cause interference degrade signal
quality
Disadvantages of Serial - Slower, synchronisation problems, receiver can't distinguish characters as
one sent after another
Asynchronous - Signals sent in previously agreed pattern. Data includes control bits which informs
receiver when transmitted data start and ends. Inexpensive serial.
Uses of serial transmission in USB - asynchronous serial, 4 wires, 2 for data other for power and
earth.
USB advantages - Automatically detected and configured upon first attachment, not possible for
incorrect instalment and industry support.
USB disadvantages - Cable limited to 5m and transmission speed to 480Mbps.
Use of parallel transmission in Integrated Circuits - Internal circuitry of computer is made up of IC's,
method of transmission is parallel, transmission channels are usually 18bit to 64bit in width, the
wider the channel the faster the transmission rate. An internal clock inside the devise makes sure all
transmitted bits arrives in sequence.
Synchronous - Transmission accompanied by timing signals ensure sender and receiver are in step.
Receiver counts bits and reassembles the data. Faster than asynchronous because less bits
sent.
Simplex - Data can only transmitted one way from sender to receiver.
Half-duplex - Data transmitted between both sender and receiver but only one way at a
time.
Full-Duplex - Data transmitted between both sender and receiver simultaneously.
Paritiy Check Verification Technique - Check byte of data, performed hen data received, parity bit
added, number of 1's counted to see if even, can be even or odd, if parity incorrect error is then
detected,
Complete Revision Summary on Data
Representation, Transmission, Hardware,
Input/Output Devices & CPU Architecture
binary numbers are used in - computer systems
conversion from denary to binary and from binary to den - use place values
memory size of a computer is measured in terms of the number of - bytes
1 kilobyte is - 2 to the 10 bytes
1 megabyte is - 2 to 20 bytes
Or 1 kilobyte according to manufactures - 1000 bytes
Increase from - kilto to mega to giga to tera
unit symbols - kilobyte-kB
megabyte, gigabyte,tera byte is- CAPITAL thenB
Each increase by - 1000 so mega byte has a 1000 kilobytes so thus a 1000000 bytes and a giga byte
has a 1000 mByte
binary registers - group of bits in computer memory, each bit does something different so if 1 then x
does y, small piece of memory built into cpu, where values and instructions are temporarily held. Not
primary or secondary, very fast read and write rate, comp systems use registers to hold values and
instructions for processing to increase the speed at which they are processed
Why choose Hex - Quicker to read, easier/quicker to write in hex, less likely to make errors copying
so easier to debug Letters in Hex - A=10
B=11
C=12
D=13
E=14
F=15
Register - Temporary piece of storage, status = stores what happening for reading, control gives
instructions for writing
MAC addresses - media access control address 12-bit identification number unique for each device.
Unique number that identifies a device, manufacturer id and serial number of device, address is
allocated by manufacturer
,Defining colours in HTML - Uses hexadecimal when representing colours, combinations of hex codes
are used to represent different colours
#FF 00 00 = primary red
#00 FF 00 = primary green
#00 00 FF = primary blue
Memory Dumps - If there is an error in program it is useful to carry out memory dump, this is
contents of a section of computer memory, Contents of a number of memory location are outputted
in Hex format, Software engineer can then look at memory dump and find where error lies. Using
Hex makes it easier and faster because ^
Assembly language and machine code - Memory location can be addressed directly using assembly
language or machine code, this means its easier for programmers to write the code because not
using binary
sound, music, pictures, video, text and number are - stored in different formats
Musical instrument digital interface - MIDI file comprises of data stored as a list of messages telling
device how to generate a sound or music. Software saves the messages as .mid file, when played on
an electronic keyboard the keyboard's software follows the .mid fil instruction and produces music,
-doesn't contain actual music so file size is much smaller than MP3 or MP4 files, 1Mbyte file size to
store one minute under MP3 and 10kbyte Midi
MPEG-3 files - uses audio compression technology to convert audio to MP3 format, normal music on
cd is compressed by a factor of 10. Uses perceptual music shaping, which removes sounds the
human ear cannot hear properly, if 2 sounds are played MP3 discards softer sound that can't be
heardeg
MPEG-4 files - format which allows multimedia rather than just audio files. Work in similar way to
MP3 but they store audio , video, photo and animation files. Work b compressing files without
affecting the quality by making certain aspects of the file redundant
Jpeg files - image encoding system that compresses photographs and other images. Lossy format and
makes use of certain properties of human vision to eliminate certain unnecessary info
Lossless file compression - breaking down into files of similar size for transmission or storage and
then put back together again at receiving end so it can be used again
Lossy file compression - Lossy compression algorithm eliminates unnecessary bits of information. It
becomes impossible to get back to the original file once this lossy compression algorithm has been
applied and the new file stored.
Algorithm looks for redundancies in file and eliminates them to reduce file size
Lossy Compression mark scheme points - images contain less detail without noticeable degradation
in quality
streams faster than lossless compression
if 2 sounds played at the same time, softer sound is removed
, when decompressed some detail is lost and file is not exactly like the original
Lossless compression mark scheme points - original and decompressed file will be the same
for code, decompressed file and original file must be exactly the same otherwise file wouldn't work
after decompression original file is restored with no loss of data
Data Transmission - Transferring binary data from sender to receiver
Serial - Data transmitted one bit at a time over a single wire
Parallel - Data transmitted several bits at a time simultaneously over several wires.
Advantages of Parallel - Faster, works well over short
Advantages of Serial - Cheaper cabling, works well over long
Disadvantages of Parallel - Conductive wires close together cause interference degrade signal
quality
Disadvantages of Serial - Slower, synchronisation problems, receiver can't distinguish characters as
one sent after another
Asynchronous - Signals sent in previously agreed pattern. Data includes control bits which informs
receiver when transmitted data start and ends. Inexpensive serial.
Uses of serial transmission in USB - asynchronous serial, 4 wires, 2 for data other for power and
earth.
USB advantages - Automatically detected and configured upon first attachment, not possible for
incorrect instalment and industry support.
USB disadvantages - Cable limited to 5m and transmission speed to 480Mbps.
Use of parallel transmission in Integrated Circuits - Internal circuitry of computer is made up of IC's,
method of transmission is parallel, transmission channels are usually 18bit to 64bit in width, the
wider the channel the faster the transmission rate. An internal clock inside the devise makes sure all
transmitted bits arrives in sequence.
Synchronous - Transmission accompanied by timing signals ensure sender and receiver are in step.
Receiver counts bits and reassembles the data. Faster than asynchronous because less bits
sent.
Simplex - Data can only transmitted one way from sender to receiver.
Half-duplex - Data transmitted between both sender and receiver but only one way at a
time.
Full-Duplex - Data transmitted between both sender and receiver simultaneously.
Paritiy Check Verification Technique - Check byte of data, performed hen data received, parity bit
added, number of 1's counted to see if even, can be even or odd, if parity incorrect error is then
detected,
