Summary
Summary Computer Science Revision Notes CIE IGCSE
A full set of notes for cie igcse computer science. Covers entire course Please note these are for the old specification (2022)
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Chapter 1 Binary systems and hexadecimalBinary
- Based on 2
- Made up of 1s and 0s
Uses of binary:
1. A register of bits 10010111
2. Robotics e.g. 1 = on, 0 = off for motor
3. Digital instruments
4. Counting systems
e.g. uses for a binary number stored in a register
address in main memory
data
ASCII value
number
instruction
Measurements:
• A binary digit is a bit
• 8 bits is a byte
• Byte is used to measure memory size
Name No. of bits Denary value
1 kilobyte (KB) 2^10 1024 bytes
1 megabyte (MB) 2^20 1024^2 bytes
1 gigabyte (GB) 2^30 1024^3 bytes
1 terabyte (TB) 2^40 1024^4 bytes
Differences between binary and denary:
Binary Denary
a base-2 system a base-10 system
uses 0 and 1 values uses 0 to 9 values
has units/ placeholders/column headings that increase has units/ placeholders/column headings that increase
by the power of 2 by the power of 10
has more digit for the same value has less digits for the same value
e.g. explain the process of converting the binary number 1010 into a denary number
- Correct column headings / place holders by example
- Correctly place a 1 or a 0 for each column
- Identify the columns to be added
- Add together the (denary) values identified...
- ...this will give a total which is the denary number/answer
- Answer is (10)
Hexadecimal
, - Base 16
- Numbers 1-9 and letters A-F used
Current uses of hexadecimal numbers in computing:
- HTML colour codes – colour codes//colour in HTML
- Error messages
- MAC addresses
- IP addresses
- Assembly language
- Memory dump // debugging
- Locations in memory
- ASCII // Unicode
Reasons for using hex
• Uses fewer characters // shorter
• Easier to read / write / understand
• Less likely to make mistakes // less error prone
• Easier to debug
Colours in HTML:
Hex can be used to represent colours on web pages and image-editing programs using the format #RRGGBB (RR =
reds, GG = greens, BB = blues). The # symbol indicates that the number has been written in hex format. Different
combinations in hex codes will create different shades/tones/colours.
MAC Addresses:
Made up of 6 pairs of hexadecimal digits, the first half is the identity number of the manufacturer of the device and
second half is the serial number of the device. Universally Administered MAC Adress (UAA) most common or Locally
Administered MAC address (LAA).
Assembly languages and machine code:
Computer memory is machine code/ assembly code
Using hexadecimal makes it easier, faster, less error prone to write code compared to binary because it can
represent 16 bit words as only 4 hexadecimal digits, and it is easy to convert hex digits back to binary if necessary.
Debugging:
Memory Dumps: Hexadecimal is used when developing new software or when trying to trace errors. The hex
number refers to the memory location of the error. This helps programmers to find and then fix problems. Memory
dump is when the memory contents are output to a printer, monitor.
Web Addresses:
Characters on a keyboard use ASCII code. These are represented using
hexadecimal or decimal values.
Why computer programmers may choose to use hex:
- It makes the values easier to read/write/understand/debug
- It is a shorter way to represent the values
- e.g. benefits of using hex notation to represent binary values
- Easier to read/write/understand (for humans)
- Easier to remember (for humans)
, - Short way to represent binary // Uses less screen/display space
- Fewer errors made (in data transcription)
- Easier to debug (for humans)
Chapter 2 Communication and internet technologies
Data transmission
Simplex Data transmission in one direction only
Half-duplex Data transmission sent in both directions but not at the same time
Full-duplex Data transmission sent in both directions at the same time. (can be
serial/parallel, not always used to connect a device to a computer, does not
automatically detect errors in data)
Serial data transmission When data is sent, one bit at a time, over a single wire or channel
Parallel data transmission When several bits of data, usually a byte, is sent down multiple wires or
channels at the same time.
Asynchronous data Data being transmitted in an agreed bit pattern.
transmission
Synchronous data Data being transmitted in a continuous stream of data.
transmission
Serial data transmission:
Used for externals usually
Advantages:
- more accurate/fewer errors over a longer distance
- Single wire – therefore can be used over longer distances
- Single wire - less expensive wiring/cheaper to manufacture or buy
- Single wire – therefore less likely to have interference // no crosstalk
- Data sent one bit at a time - less chance of data being skewed/out of synchronisation/order // data received in
order
- Transmission can be synchronised – can reduce the rate of errors
Disadvantages:
- Slower than parallel
Example of use
- Connect computer to a modem
- USB cables
- HDMI cables
- Universal Serial Bus (USB)
Parallel data transmission:
Used for internals usually
Usually used only on short distances because over long distances the data will skew and ‘merge’ between the two
wires or channels.
Uses several/multiple wires, transmits multiple bits at a time
, Advantages:
o Transmitted at a faster rate
Disadvantages:
- Only supports short distances (becomes skewed over long distance – bits travel at different speeds)
- More chance of data being skewed due to bits being sent simultaneously/out of order
- More expensive as requires several/multiple wires
Example of use
o Integrated circuit because data is transmitted over a short distance and there is no risk of skewing of
data.
o Integrated circuits – parallel transmission, for sending data internally
o RAM
o Connections to peripheral devices
You need to check for errors because data is easy to corrupt/skew. You also don’t want wrong data.
Simplex Examples:
• Microphone to computer
• Sensor to computer
• Computer to printer
• Computer to speaker
• Computer to monitor
• Webcam to computer
• Sending data to a device // sending data from a device
Duplex Examples.: Telephone call
- Voice over IP
- Computer to printer (only award once)
- Instant messaging
- Broadband connections
- Video conferencing
- Sending data to and from devices e.g wireless technology
- Computer to modem
- -> will allow read and write at the same time
Parity bits
USB
- Asynchronous serial
- Four wire shielded cable
- Two wires for power and earth
- Two wires for data transmission
Three things that happen when a device is plugged into a USB port:
• The computer automatically detects that a device is present(this is due to a small change in voltage level on
the data signal in the cable)
• The device is automatically recognised, and the appropriate device driver is loaded up so that the computer
and device can communicate effectively.
• If a new device is detected, the computer will look for the device driver which matches the device; if this is
not available, the user is prompted to download the appropriate software.
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