Memory, storage and units of size

Step 1 Warm-up recall

From Module 2: how many bits make a byte?

Your answer

Private: nothing you type here is sent or stored.

Step 2 Learning goal

By the end of this lesson you can:

• convert between bytes, KB, MB and GB (Foundation);
• estimate how many files fit (Core);
• explain the speed and size pattern of memory (Core).

Step 3 A familiar example

A desk is quick to reach but small. A warehouse is large but far away. Computers use the same pattern: fast memory is small and costly, and slow storage is big and cheap.

Step 4 Clear explanation

Data is measured in bytes, and one byte is 8 bits (Module 2). Larger units use prefixes. This course uses the decimal prefixes, in which each unit is 1,000 times the one before. Note that some software uses 1,024 instead, so figures may differ slightly between tools.

To estimate how many files fit, convert both sizes to the same unit and divide. An invented example: a 4 GB card is 4,000 MB, and photos of 2 MB each fill it with 4,000 ÷ 2 = 2,000 photos. For speed, the general pattern is shown below.

The processor works fastest with the data closest to it, so computers keep small amounts of data in very fast memory and large amounts in slower storage. The figure shows the pattern only; exact sizes and speeds change with each new machine and are not given here. Keep the pattern in mind when you read a product description: more memory lets more programs and data stay close to the processor, while more storage holds more files.

Step 5 Worked example (4 marks)

A drive holds 500 GB. How many 25 MB files fit, using decimal units?

1. Convert: 500 GB = 500,000 MB. (1 mark)
2. Divide: 500,000 ÷ 25. (1 mark)
3. 500,000 ÷ 25 = 20,000. (1 mark)
4. Answer: 20,000 files. (1 mark)

Step 6 Learner practice (instant-marked)

Step 7 Recap

• Convert to one unit, then divide.
• Decimal prefixes step by 1,000.
• Faster memory is smaller; storage is larger and slower.

Step 8 Exit ticket (ungraded)

How many 4 MB files fit in 2 GB?

Your answer

Private: nothing you type here is sent or stored.

Step 9 Go further (Extension)

Check the units on a real device and note whether it uses 1,000 or 1,024.