Data Capacity & Calculating Capacity Requirements (OCR GCSE Computer Science)

What is data capacity?

• Data capacity is the maximum amount of information that a storage device can hold
• If you know the capacity of a storage device, you can calculate how much of different data types can be stored
• Examples of data that could be stored include text, images and sound files

How do you calculate capacity requirements?

• To calculate capacity requirements you need to:
  
  • Know the capacity of the storage device
  • Calculate the size of a file (formula)
  • Ensure the same units of data storage are used for capacity and size of the file, else convert between units to get them to be the same
  • Divide the capacity by size of the file being stored

• The image above shows common capacities of storage devices such as hard drives (HDD), USB flash drives, solid state drives (SSD) and optical disks (CD)

Calculating file sizes

Text Files

(Bytes per character) x (Number of characters)

Size of text file =      Bytes per character 1 Based on Extended ASCII character set being used (8 bits) Number of characters 2000 Including spaces! 1 x 2000 = 2000 bytes = 2 KB

Image Files

(Resolution) x (Colour Depth)

Size of image file =      Resolution 500 x 500 Resolution = Width x Height Colour Depth 24 bits 24 bits = 3 bytes (500x500) x 24 (500x500) x 3 = = 6,000,000 bits 750,000 bytes = 75 KB

Sound Files

(Sample Rate) x (Duration in seconds) x (Bit Depth)

Size of sound file =      Sample Rate 10 Samples per second Duration 30 Seconds Bit Depth 4 Number of bits stored per sample 10 x 30 x 4 = 1200 bits = 150 bytes