[2] Handling many concurrent connections is a different problem from handling many requests per second: the latter requires high throughput (processing them quickly), while the former does not have to be fast, but requires efficient scheduling of connections.
This can involve a combination of operating system constraints and web server software limitations.
According to the scope of services to be made available and the capabilities of the operating system as well as hardware considerations such as multi-processing capabilities, a multi-threading model or a single threading model can be preferred.
[2] The term C10k was coined in 1999 by software engineer Dan Kegel,[3][4] citing the Simtel FTP host, cdrom.com, serving 10,000 clients at once over 1 gigabit per second Ethernet in that year.
[1] The term has since been used for the general issue of large number of clients, with similar numeronyms for larger number of connections, most recently "C10M" in the 2010s to refer to 10 million concurrent connections.