CS02-05 Computer Science Coming soon
Working out the size of a text file
CS02-05
This lesson is coming soon.
In this lesson
Calculate the size of a text file from the bits per character and the number of characters, convert the answer into sensible units, and work out the storage capacity required for a set of files.
What it covers
- Text file size in bits = bits per character x number of characters (OCR prints this formula and it is NOT given in the exam)
- Which bit count to use, per board - 7 for AQA and Edexcel, 8 in an OCR exam - taken as settled from CS02-02, not re-argued
- Bits to bytes is DIVIDE BY 8, and it is a separate step from the prefix step - two divisions, never one
- Converting the result into kilobytes or megabytes on AQA and OCR, and into kibibytes or mebibytes on Edexcel
- Storage capacity for a SET of files: work out one, then multiply by how many
- Showing working, because the marks sit in the steps and not only in the final number
- One line on metadata: OCR states that an allowance for metadata in calculations may be used, so a real file is slightly bigger than the characters alone
Key words
For: AQA GCSE 8525, Edexcel GCSE 1CP2, OCR GCSE J277
On the specification
| Board | Spec | Statement |
|---|---|---|
| AQA GCSE 8525 | 3.3.3 | State that a bit is the fundamental unit of information and a byte is 8 bits, use the decimal prefixes kilo, mega, giga and tera, and compare quantities of bytes. |
| Edexcel GCSE 1CP2 | 2.3.1 | Data storage and compression |
| OCR GCSE J277 | 1.2.3 | Units |
For teachers
This GCSE Computer Science lesson teaches working out the size of a text file. By the end, students should be able to calculate the size of a text file from the bits per character and the number of characters, convert the answer into sensible units, and work out the storage capacity required for a set of files. It works through four worked examples and the mistakes examiners report.