Why will Ubuntu no longer measure file size unit as byte, megabyte, gigabyte, etc?

Short answer is yes, the prefixes change. But it doesn't really make a difference.

Reasoning

There has always been confusion because decimal-style units like KB, MB, GB were used with binary data - KB meant 1024 bytes, not 1000 bytes as might be expected. And of course many people throughout the world use the actual decimal prefixes in their daily lives under the metric system.

Network engineers and long-time computer users of course are trained to understand the difference, but the ongoing confusion meant applications were inconsistent in their usage; one application might use MB to mean 1,000,000 bytes (using the decimal prefix), while another might mean 1,048,576 bytes (using the binary interpretation).

This led to Ubuntu eventually adopting a new units policy.

Impact

The impact is really just a display issue. File sizes and network bandwidth will be displayed using the decimal prefixes, so a 5kB file will actually be 5000 bytes. This is actually in line with what many (most?) people expect.

Memory usage and some low-level utilities will display sizes using the binary prefixes (KiB, MiB, GiB, TiB). This may cause some initial confusion but is actually better than the status quo where we have one prefix meaning two different things.

Since Windows still uses the old, ad-hoc system a Wine application might display slightly different file sizes for the same file. However I at least often see different sizes displayed anyway due to rounding methods, so I'm not convinced it's a major issue.

See also:

• What file size units do applications on Ubuntu use?