Units of Data Storage (OCR GCSE Computer Science): Revision Notes

Units of Data Storage

Binary System and Data Storage

• Binary is a number system that uses only two symbols: 0 and 1.
• Computers can only process data in binary because they only understand machine code, which consists of 0s and 1s.
• A single 0 or 1 in binary is called a bit.

Data Units and Their Sizes

• Bit (b): A bit is the smallest unit of data and represents either 0 or 1.
• Nibble: A nibble is made up of 4 bits (e.g., 1010).
• Byte (B): A byte consists of 8 bits (e.g., 10101010).

Common Units of Storage

Unit	Size in Bytes	Size in Bits
Bit	1/8 byte	1 bit
Nibble	1/2 byte	4 bits
Byte (B)	1 byte	8 bits
Kilobyte (KB)	1,024 bytes	8,192 bits
Megabyte (MB)	1,024 KB	8,388,608 bits
Gigabyte (GB)	1,024 MB	8,589,934,592 bits
Terabyte (TB)	1,024 GB	8,796,093,022,208 bits
Petabyte (PB)	1,024 TB	9,007,199,254,740,992 bits

Why Data is Stored in Binary Format

• All data must be converted into binary (1s and 0s) for the computer to process it.
• Text, images, sound, and instructions are translated into binary to be stored and processed by a computer.

Calculating Data Storage Capacity

You need to be familiar with calculating the storage size of files, which varies depending on the type of data:

• Sound file size = sample rate (Hz) × duration (s) × bit depth (bits per sample)
• Image file size = colour depth (bits per pixel) × image height (pixels) × image width (pixels)
• Text file size = bits per character × number of characters