CCEA GCSE Digital Technology

Data and information

Data is a raw collection of facts, figures or symbols that has no meaning by itself. The number 67, the word "Belfast" and the date 18/05/2023 are all data. Information is data that has been processed, organised or put in a context so that it means something to a person. A list of test marks is data; a statement that the class average was 67, with the marks sorted and labelled by subject, is information, because someone can now act on it.

The same item can be either depending on context. A value of 57 on its own tells the reader nothing, but 57 in a column headed "Communications mark" is information. Computers store and process data, and the software that presents the results is what turns it into information.

Units of storage

A computer stores everything as binary digits. A bit (binary digit) is the smallest unit of data and holds either 0 or 1. Bits are grouped so that larger amounts can be described.

A byte is the amount normally used to store one character of text, which is why file sizes are given in bytes and their multiples. The factor of 1,024 is $2^{10}$ and follows from computers counting in binary; some manufacturers of storage devices round it to 1,000 when they advertise capacity, which is why a drive can appear slightly smaller than its label once a computer reports it.

The number of different patterns that $n$ bits can hold is $2^n$. A nibble can therefore hold $2^4 = 16$ different values and a byte can hold $2^8 = 256$, which is why a single byte can represent the whole numbers from 0 to 255.

Converting between units

To move to a smaller unit, multiply by 1,024; to move to a larger unit, divide by 1,024.

A photograph of 3 MB is $3 \times 1{,}024 = 3{,}072$ KB, and since each kilobyte is 1,024 bytes it holds $3{,}072 \times 1{,}024 = 3{,}145{,}728$ bytes. A video of 2,048 MB is $2{,}048 \div 1{,}024 = 2$ GB.

A storage device of 500 GB can hold 500 files of 1 GB, or $500 \times 1{,}024 = 512{,}000$ files of 1 MB, before it is full.

Data types

Every item of data in a program, spreadsheet or database has a data type, which says what kind of value it is and therefore how it can be stored and what can be done with it. Choosing the right type matters because it decides how much storage the item needs, which operations are allowed (you can add two numbers but not two names) and what the software will reject as invalid.

Integer and real are the two kinds of numeric data. Use an integer for anything that is counted, such as the number of students in a class, and a real number for anything that is measured or can be fractional, such as a height in metres or a price.

Digits that are not numbers

A telephone number, a postcode or a student code such as CM101 is made of digits and letters, but arithmetic on it would be meaningless, so it is stored as a string. A phone number also often begins with a zero, which a numeric field would drop because a leading zero does not change the value of a number. Storing 07700 900123 as a string keeps every digit exactly as typed.

Date and time

Date and time values are stored as their own type, not as strings, because the software can then work with them: it can sort dates into order, find the number of days between two dates, and reject 31/02/2024 as impossible. A date typed as text would sort alphabetically, putting 02/01/2024 before 15/12/2023.

Choosing a type