Starcraft AI blog

The standard build order for 12 hatchery is this. The initial overlord provides 8 supply and the hatchery provides 1 supply, for a total of 9 until the second overlord spawns.

- 4 drones (8 total)
- overlord @ 8
- 1 drone (9 total, supply limit)
- ... wait for overlord to finish
- 3 more drones (12 total)
- hatchery

Many zerg bots follow the standard build. I’m making this post because some zerg bots follow a different build:

- 5 drones (9 total, supply limit)
- overlord @ 9
- ... wait for overlord to finish
- 3 more drones (12 total)
- hatchery

It may seem to make sense. Don’t you mine more minerals if you make the 9th drone as early as possible? But in fact the standard build is a tiny bit better. It’s standard for good reason.

Here are the timings. “12 drones” is the time when the 12th drone starts. “Hatchery” is when the hatchery starts.

In these runs, the 12th drone was started on exactly the same frame for both builds. The 12th drone is larva limited for both builds; after the overlord finishes, you have only 2 larvas and have to wait for the next one to get the last of the additional 3 drones. There is a bit of randomness in larva timing, so the exact frame can vary. Furthermore, the 9th drone really does mine more minerals before then; with the overlord on 9, zerg has slightly more minerals when the 12th drone starts. Nevertheless, the hatchery starts a little sooner if you make the overlord on 8! Why is that?

You don’t care about the mineral count when the 12th drone starts. You care about how soon you can get to 300 minerals for the hatchery. If you make the 9th drone before the overlord, 1 drone mines a little longer, and 2 drones are delayed waiting for the overlord to provide supply. If you make the 9th drone after the overlord, those 2 drones start mining sooner. The extra mining time of the 2 drones after the overlord (in the standard build) outweighs the mining time of 1 earlier drone before the overlord (in the other build).

The difference is very small. At bot level of play, it probably has almost no effect on who wins. If you play the “wrong” build, then you surely have more important things to fix first! Nevertheless, the standard build is superior, and it should be easy to switch to it.

Similar timing calculations are behind the standard terran supply depot @ 9 and the standard protoss pylon @ 8. The general topic is: What is the most efficient time to order supply? Too early and you tie up minerals that you could have spent better; too late and the supply block holds you back. In general, there is an optimal answer (at least there is provided you can predict your combat losses), and it depends on what you intend to make next.