1.2.3 Units

Computers store and process data using binary, so the amount of data is measured using units based on bits and bytes. A bit is the smallest unit of data and can have a value of either 0 or 1. A group of 8 bits makes 1 byte. Larger amounts of data are measured using the following units:

For example, a 5 GB file contains approximately 5,000 MB, or 5,000,000 KB.

Conversions

When converting between units, move up or down the table by multiplying or dividing by 1,000. When converting between bits and bytes, remember that 1 byte = 8 bits.

It is common to see storage devices described using these units. A smartphone might have 128 GB of storage, while a large organisation might store several terabytes or petabytes of data.

Now here’s the tricky bit…

You may sometimes see computer storage described using 1024 rather than 1000. This is because computers work in binary, so 1024 is a convenient value: 1024 = 2¹⁰. You may therefore come across calculations such as 1 KB = 1024 bytes, particularly in older computing resources or when discussing memory.

For this course, however, use the values given in the question and assume to use 1000s, instead of 1024s. You do not need to worry about this in the exam. OCR does not expect you to memorise the 1000/1024 distinction, and the exams do not allow calculators. For straightforward unit conversions, the numbers will be chosen so that you can work them out without one. The questions should accept answers where you’ve used 1024 instead of 1000 though, but it is not recommended.