Why is Download Speed Measured in Bits and File Sizes in Bytes?

Why download speed is measured in bits while file sizes are in bytes? Learn about communication engineering standards and more.

Why is Download Speed Measured in Bits and File Sizes in Bytes?
Photo by Shubham Dhage / Unsplash

If you've ever wondered why download speed is measured in bits per second (Mbps or Gbps) while file sizes are measured in bytes (KB, MB, GB), you're not alone.

There are specific reasons for these contrasting measurements, and understanding them is crucial for a deeper insight into data communication and digital storage.

Different Units

When it comes to measuring download speed, such as when you are checking your internet connection, the units most commonly used are bits per second (bps), kilobits per second (Kbps), megabits per second (Mbps), and gigabits per second (Gbps).

On the other hand, file sizes are often measured in bytes, kilobytes (KB), megabytes (MB), gigabytes (GB), and so on.

Origin of Measurements

The reason for the discrepancy lies in the historical development of computing and data communication.

The concept of a 'bit' is fundamental to digital technology, as it represents the smallest unit of data.

This is why download speeds, which are a measure of data transmission rates, are expressed in bits per second.

Usability and Practicality

File sizes are generally measured in bytes because this unit is more practical for representing the sizes of files and storage capacities.

For instance, it would be arduous to express a file size of 1 GB in bits, as it would result in a much larger number (8 billion bits) which is not as manageable or user-friendly.

Engineering and IT Standards

Communication engineers typically measure in multiples of precisely 1000, and file sizes in IT have been standardized as 8-bit bytes (octets) for many years.

However, multiples of 1024 are also commonly used in IT contexts, leading to the use of both Gbps and GB per second (or GiB per second) depending on the context.

Raw Bit Rate vs. Actual Transfer Rate

Additionally, Gbps represents the raw bit rate, while the actual file transfer rate includes various overheads that prevent data transfer at the full rate.

This actual file transfer rate is represented in terms of GB per second (or GiB per second), which provides a more accurate depiction of the rate of transfer.

Provoking Thought

The discrepancy between the measurements of download speed and file sizes is a reflection of the historical and practical considerations in computing and data communication.

While it may seem inconvenient, these contrasting measurements are a result of specific technological and usability factors in engineering and IT standards.