Network speeds (Edexcel GCSE Computer Science): Revision Notes
Network speeds
What is network speed?
Network speed refers to how fast data can move from one device to another across a network. More technically, it's called the data transfer rate - this measures the number of bits that can be transferred in a specific period of time.
Since modern technology can handle huge amounts of data very quickly, network speeds are typically measured in megabits per second (Mbps) rather than just bits per second.
Units for measuring data transfer rates
Data transfer rates (network speeds) are measured using base-10 units, which means each step up multiplies by 1000:
| Unit | Abbreviation | Number of bits |
|---|---|---|
| Bits per second | bps | 1 |
| Bytes per second | Bps | 8 |
| Kilobits per second | Kbps | 1,000 |
| Megabits per second | Mbps | 1,000² (1,000,000) |
| Gigabits per second | Gbps | 1,000³ (1,000,000,000) |
Notice that bytes per second uses a capital 'B' while bits per second uses a lowercase 'b'. This is important because 1 byte = 8 bits!
Units for measuring file sizes
File sizes are measured using base-2 units, which means each step up multiplies by 1024:
| Unit | Abbreviation | Number of bits |
|---|---|---|
| Bit | 1 | |
| Byte | 8 | |
| Kilobyte | KiB | 1024 × 8 |
| Megabyte | MiB | 1024² × 8 |
| Gigabyte | GiB | 1024³× 8 |
| Terabyte | TiB | 1024⁴ × 8 |
Key difference: Data transfer rates use base-10 (×1000) while file sizes use base-2 (×1024). This is crucial for calculations!
The network speed formula
To work out how long it takes for a file to be transmitted across a network, you can use this formula:
You can rearrange this formula to find any missing value when you have the other two:
Worked examples
Worked Example 1: Finding transmission time
Question: A 55 MiB file is transmitted across a network at a transmission rate of 38 Mbps. Construct an expression to calculate how many seconds it will take to transmit the file.
Solution steps:
- Convert the file size to bits:
- Convert the data transfer rate to bits per second:
- Apply the formula: Time = File size ÷ Data transfer rate
Expression:
Worked Example 2: Finding network speed
Question: A 15 GiB file takes 18 seconds to download. Construct an expression to calculate the speed of the network in megabits per second.
Solution steps:
- Convert file size to bits:
- The time is already in seconds: 18
- Calculate speed in bps, then convert to Mbps by dividing by
Expression:
Exam tips
When approaching network speed problems in exams, there are several essential strategies to keep in mind for success.
Critical Exam Guidelines:
- Always check your units! Make sure file sizes are in bits and speeds are in bits per second before using the formula
- Remember the difference: File sizes use base-2 (×1024), speeds use base-10 (×1000)
- Show your working: In exams, you often get marks for setting up the correct expression, even if you don't calculate the final answer
- Unit conversions: When converting file sizes to bits, multiply by 8 at the end (since 1 byte = 8 bits)
Summary
Understanding network speeds requires mastering the relationship between data transfer rates, file sizes, and transmission times.
Key Points to Remember:
- Network speed is the data transfer rate - how many bits can be sent per second
- Data transfer rates use base-10 units (×1000): bps, Kbps, Mbps, Gbps
- File sizes use base-2 units (×1024): bytes, KiB, MiB, GiB, TiB
- Key formula: Time = File size (in bits) ÷ Data transfer rate (in bps)
- Always convert file sizes to bits and speeds to bits per second before calculating
- In exams, you often just need to construct the expression, not calculate the final answer