Summary
Summary AS2 Digital Technology Revision notes
- Module
- Digital technology
- Institution
- GCSE
AS2 Digital Technology Revision notes Including specification points
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Unit AS 2: Fundamentals of DigitalTechnology
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Data representation
Bits and bytes
• explain the terms bit, byte, kilobyte, megabyte, gigabyte and terabyte;
Bit - A Binary digIT. The smallest unit of data stored by a computer. Represented by a 0 or 1
Byte - A group of 8 bits in a character.
Kilobyte - 1024 bytes = 210 bytes
Megabyte - 1024 kilobytes = 220 bytes
Gigabyte - 1024 megabytes = 230 bytes
Terabyte - 1024 gigabytes = 240 bytes
• demonstrate that 2n different values can be represented with n bits (maximum n = 8);
28 27 26 25 24 23 22 21 20
256 128 64 32 16 8 4 2 1
Binary and decimal
• perform conversions from decimal to binary and from binary to decimal for a maximum of 8 bits;
• demonstrate how the two’s complement system can represent positive and negative numbers in
binary using 8 bits;
- The most significant bit (MSB) is used as a sign bit.
- If it is 0 the number is positive. If it is 1 the number is negative.
- For a positive number place values are used.
- Twos complement:
1. invert the bits of its positive equivalent
2. and add 1 to the least significant bit (LSB).
3. The most significant bit (MSB) is used as a sign bit.
• demonstrate how American Standard Code for Information Interchange (ASCII) and Unicode are
used to represent characters;
Character set
- A range of characters and symbols that can be represented by a unique binary code for each
, character.
- These include displayable characters, digits, punctuation and control codes.
American Standard Code for Information Interchange (ASCII)
- A character set that had a 7-bit set of codes that allow 128 different characters.
- 96 displayable characters and 32 control codes.
- Only used in the English language
- An 8th bit can be used as a parity bit for error checking.
- 8 bits can be used to represent 256 characters and control codes: Extended ASCII.
Unicode
- Uses 16 to 32 bits to represent 65536 characters.
- For most languages from around the world.
- May take up more storage space.
- Can take longer to process.
Data and information
Data, information and knowledge
• distinguish between data, information and knowledge by using examples;
Data
- Raw facts and figures with no meaning.
Information
- processed data that has meaning.
Knowledge
- The result of applying rules to information to assist decision making.
• describe how the quality of the information produced can be affected by the following factors:
- Accuracy, relevance, up to date/currency, completeness, presentation and reliability.
Up to date
- If you are asked to attach a photograph of yourself to your university application and you
upload a photo of you on your 8th birthday, is this up to date?
Relevance
- Data must be relevant for its intended purpose
Completeness
- You get a phonecall from Next about coming for an interview for a part time job. You thank
them and they end the call. They did not give you the date, time or location of the interview.
The information in incomplete
Reliability
- You are due to start University of Ulster next September and you ask for the start date. A
, person who just started Queen's tells you that you start on the 5th September. Is this
information from a reliable source?
Accuracy
- Data does not have to be 100% accurate but it should be accurate enough for the purpose.
Presentation
- When a house is being advertised for sale pictures are included in the brochure to make it
easier to decide
ARCPUR
Data validation and verification
• describe and apply the following data validation methods:
- range, type, length, format, presence, Modulus 11 check digit and lookup;
Range check
- Ensures that data is within a lower and upper limit.
Type check
- Checking that data value is of the correct type e.g. text, numeric, Boolean, Date/Time
Length check
- Checks that the data value contains a certain number of characters.
Format check
- Ensures that data matches a predefined pattern.
Presence check
- Data must be entered as it is mandatory.
Lookup
- Data value entered is compared against a predefined list of data values which the computer
will find a match.
Modulus 11 check digits
- AN EXTRA DIGIT ADDED AS PART OF A NUMBERIC DATA ITEM
- If the remainder is 0 there is a result of 11 so the check digit is 0
- If the remainder is 1 there is a result of 10 so the check digit is X
• understand the purpose of the following data validation methods:
- check digits; and
- batch totals (hash and controls);
How effective is the check digit at detecting transposition errors?
- A check digit can detect most transposition errors
- TRANSPOSITION ERROR: where two adjacent characters are switched.
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