Byte per second to Kibibyte per second

Files are stored in bytes because CPUs address memory in byte-sized (8-bit) chunks — the smallest unit a program can read or write. Networks measure in bits because physical signals on a wire or fiber are serial: one bit at a time, clocked at a specific frequency. A 1 GHz signal produces 1 Gbps, not 1 GBps. The two worlds evolved independently and neither adopted the other's convention, leaving users to divide by 8 forever.

In modern computing, yes — a byte is universally 8 bits. Historically, some architectures used 6, 7, or 9-bit bytes, which is why the unambiguous term "octet" exists in networking standards. But for all practical bandwidth conversions today, 1 byte = 8 bits.

Network protocols add overhead — TCP headers, encryption (TLS), error correction, and packet framing all consume bandwidth without contributing to file data. A 100 Mbps connection might deliver 11 MB/s instead of the theoretical 12.5 MB/s because 10–15% goes to protocol overhead.

USB 3.0 has a theoretical maximum of 625 MB/s (5 Gbps ÷ 8), but real-world sustained transfers hit 300–400 MB/s due to protocol overhead and controller limitations. USB 3.2 Gen 2 doubles this to about 700–900 MB/s in practice.

The bit came first, coined by Claude Shannon in 1948. The byte was introduced at IBM in the mid-1950s by Werner Buchholz to describe the smallest addressable group of bits in the IBM Stretch computer. Originally it could be any size; the 8-bit byte became standard with the IBM System/360 in 1964.

Rsync follows IEC binary conventions because it deals with file sizes that are measured in binary units by the filesystem. Since files occupy whole filesystem blocks (typically 4 KiB), reporting transfer speed in KiB/s makes the math consistent with actual data moved on disk.

1 KiB/s (1,024 bytes/second) is 2.4% faster than 1 kB/s (1,000 bytes/second). The difference is tiny at this scale but matters when you are designing buffer sizes for embedded systems where every byte of RAM counts.

Microsoft started using binary units more consistently in Windows 10 after years of ambiguity where "KB" sometimes meant 1,000 and sometimes 1,024 bytes. The shift toward KiB follows IEC recommendations and reduces confusion, though the transition is still incomplete across all Windows tools.

A 3.5-inch floppy drive transferred data at about 31–62 KiB/s (250–500 kbps). Copying a full 1.44 MB floppy took roughly 25–50 seconds. For comparison, a modern NVMe SSD is about 100,000 times faster.

In embedded systems with tight memory constraints, confusing 1,024 with 1,000 can overflow a buffer. In network protocols, a spec written in KiB/s being implemented as kB/s means transmitting 2.4% less data than expected per second — enough to cause timing violations in real-time systems.