Kilobyte per second to Gigabyte per second

A typical 4 MB MP3 file at 7 kB/s took about 9–10 minutes to download. Napster users in 1999 would queue up songs before bed and hope the phone line stayed connected overnight. A single disconnection meant starting over from scratch.

Lowercase "k" with uppercase "B" (kB/s) means 1,000 bytes per second (SI decimal). Uppercase "K" with uppercase "B" (KB/s) traditionally meant 1,024 bytes per second (binary). In practice, most software uses them interchangeably, and the difference is only 2.4%.

Apps display kB/s when transfer speeds are genuinely that slow — downloading over congested mobile networks, tethering in rural areas, or transferring tiny files where the connection never ramps up. It is also common in SSH/SCP transfers that display instantaneous speed during small file copies.

The first consumer ADSL plans offered 256 kbps downstream, delivering about 32 kB/s — roughly 4.5× faster than a 56k modem. A 512 kbps plan gave 64 kB/s. That first jump from 7 to 32 kB/s felt revolutionary, cutting a 10-minute download to about 2 minutes.

An SMS is limited to 140 bytes (160 characters in GSM-7 encoding), and the signalling channel transmits it almost instantly. But if you think of SMS throughput over a sustained period, the practical rate is about 0.1–0.5 kB/s because of the overhead between messages.

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.