OCR J277 Topic 1.2 Maths

Data Units & Storage

Complete lesson with Foundation & Extension challenges.

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1

Units & The 1000 Rule

The Smallest Units

  • Bit (b): 1 or 0.
  • Nibble: 4 bits.
  • Byte (B): 8 bits.

The Conversion Rule

OCR uses 1000 (not 1024).

MB GB (Divide by 1000)
Foundation

A game update is 5000 MB. Calculate the size in GB.

5000 ÷ 1000 = 5 GB
Extension

A text file has 400 characters (1 byte each). Calculate the size in bits.

400 Bytes × 8 = 3200 bits
2

Total Capacity

The Formula

Simply multiply the Number of Files by the Size of one File.

Tip: Always check if the question asks for the answer in a different unit (e.g. MB vs GB)!
Foundation

Sarah takes 200 photos. Each is 5 MB. What is the total size in GB?

200 × 5 = 1000 MB
1000 ÷ 1000 = 1 GB
Extension

A server has a 2 PB drive. The school adds 100 TB per year. How many years to fill it?

2 PB = 2000 TB
2000 ÷ 100 = 20 Years
3

The "Available Space" Trap

Exam Warning

If a question says "64GB Total Storage, 10GB Used", you MUST subtract first.
Only calculate with the 54GB Available.

Foundation

A 16 GB USB stick has 12 GB used. How many 2 GB videos can fit?

16 - 12 = 4 GB Free
4 ÷ 2 = 2 Videos
Extension

Phone: 64 GB total. System uses 14 GB. App size: 500 MB. How many apps?

64 - 14 = 50 GB Free
50 GB = 50,000 MB
50,000 ÷ 500 = 100 Apps
4

Bitmap Images

The Formula

Width × Height × Colour Depth = Size (bits)

Don't forget to divide by 8 to get Bytes, then 1000 to get KB!
Foundation

Image: 100 × 100 pixels. Colour Depth: 8 bits. Size in KB?

100×100 = 10,000 pixels
10,000 × 1 Byte = 10,000 Bytes
10,000 ÷ 1000 = 10 KB
Extension

Icon: 50 × 50 pixels. Colour Depth: 16 bits. Size in KB?

50×50 = 2500 pixels
2500 × 16 = 40,000 bits
40,000 ÷ 8 = 5,000 Bytes
5,000 ÷ 1000 = 5 KB

Lesson Summary