GoKawiilIn 2004 I played too much RuneScape on a 56k modem that died the moment Mum picked up the phone. A 3D world, up to a couple of thousand players on a server, dozens on screen at once - in the browser, on 5 kilobytes per second. It worked. Let’s follow a single step and see how.
As a child I was too preoccupied with picking flax and killing goblins to think about how this worked. The answer, however, is a sustained, almost obsessive exercise in not wasting bytes. So, let’s click one tile north of where we’re standing, and trace every byte that crosses the wire from that click, to the server, to the screen of another player.
Central fountain, Varrock Square
The detail in this post comes from a decompiled 2004 RuneScape 2 client. Snippets are rough translations from that decompile, tidied up in places for readability but with the logic intact.
The core principles aren’t identical across versions, but most of them run all the way from RuneScape Classic (2001) to present-day RuneScape 3 and, of course, Old School RuneScape.
If you played RuneScape in the early 2000s and are still in possession of a hard drive from that era, please check out the RuneScape Archive Project. They do great work to catalogue historic RuneScape versions which are otherwise lost to time, and every contribution is valuable.
Let’s look at some of the constraints that Jagex were working with at the time.
Bandwidth. A 56k modem syncs at 56 kilobits per second downstream, and less upstream, minus any protocol overheads and line noise. Call it 5 KB/s down and a lot less up. Broadband was available in British homes by 2000, but it wasn’t until the late 2000s that the majority of UK households had a broadband connection, so plenty of players were on dial-up.
A 56k modem syncs at 56 kilobits per second downstream, and less upstream, minus any protocol overheads and line noise. Call it 5 KB/s down and a lot less up. Broadband was available in British homes by 2000, but it wasn’t until the late 2000s that the majority of UK households had a broadband connection, so plenty of players were on dial-up. Java applet, in a browser, in 2004. Java applets ran in a security sandbox, which meant no raw native sockets and no UDP. Every byte travelled over a single TCP connection, in-order and with per-segment overhead.
Java applets ran in a security sandbox, which meant no raw native sockets and no UDP. Every byte travelled over a single TCP connection, in-order and with per-segment overhead. A 600ms server cycle. The RuneScape game server advances in discrete cycles (or ticks) of roughly 600 milliseconds. Every cycle, for every player, the server has to work out everything that player can now see and ship it before the next one.
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