Byte per second to Gigabyte 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.

CPUs constantly shuttle data between RAM and their caches. DDR5-6000 provides about 96 GB/s of bandwidth in dual-channel mode. In games, insufficient RAM bandwidth causes frame drops during complex scenes. In productivity tasks like video encoding, it directly limits how fast the CPU can process data.

Thunderbolt 4 runs at 40 Gbps, which is 5 GB/s. Thunderbolt 5, released in 2024, doubles this to 80 Gbps (10 GB/s) with a burst mode up to 120 Gbps (15 GB/s). This is fast enough to run an external NVMe SSD at near-internal speeds.

Both, depending on generation. A PCIe 3.0 ×4 interface caps at ~3.5 GB/s, bottlenecking modern NAND. PCIe 4.0 ×4 raises this to ~7 GB/s, and PCIe 5.0 ×4 to ~14 GB/s. The drive's NAND flash and controller also have limits — the fastest SSDs and the fastest interfaces are in a constant leapfrog.

GPUs use wide memory buses (256–384 bits) with very fast HBM or GDDR6X memory running at high clock speeds. An RTX 4090 has a 384-bit bus with GDDR6X at 21 Gbps per pin, totalling 1,008 GB/s. HBM3 in data center GPUs achieves 3,000+ GB/s through stacked memory with 4096-bit buses.

At multi-GB/s rates, CPU processing speed, software efficiency, and thermal throttling become bottlenecks. A 14 GB/s PCIe 5.0 SSD can deliver data faster than most applications can consume it. Decompression, parsing, and memory allocation in software often cannot keep up with raw storage bandwidth.