How do patches work?

[dux]

What I mean is, I just reinstalled Diablo 2 the other week and the latest patch 1.12 is around 30-40mb. And there have been a lot of patches for Diablo 2 over the years all averaging 30-40mb. As I was installing it and looked through the version histories I wondered how do they include all the previous fixes and only have it accumulate to 30-40mb everytime? If the fixes were all included in every patch wouldn't it be totalling around 100-200+ mb by now? It is late so maybe I'm being slow about this.

[Taylor]

Because the patches contain revised versions of the same files and overwrite them.

IIRC whenever there's a new patch it just dumps all the new information into patch.mpq (Blizzard archive) overwriting as it goes, and the game itself just loads whatever is in the patch.mpq with a prority over the release mpq's. If they've changed all the monster and item files every patch then you don't store (and have no need to store) every revision. I imagine most of the updates to Diablo II are along the lines of stat tweaks, opposed to new graphics.

[Jetsetlemming]

Actually overwriting the files that are updates is inefficient- Diablo 2 and LOD together is just under 2 gigs total of data. Intelligent patch installers can find the file it needs to update, and change it to match the new version instead of fully deleting it and copying over a full copy of the new one.

[Sentura]

Actually overwriting the files that are updates is inefficient- Diablo 2 and LOD together is just under 2 gigs total of data. Intelligent patch installers can find the file it needs to update, and change it to match the new version instead of fully deleting it and copying over a full copy of the new one.

uhh... yeah, that's called overwriting. patching is like using svn/subversion; it makes sure the files are in sync.

[Thrik]

I think he meant it only changes the part of the file that's changed, which is what some games' patchers do.

[Sentura]

I think he meant it only changes the part of the file that's changed, which is what some games' patchers do.

yeah but that's still overwriting.

[Defrag]

It probably just does a binary diff on a load of files. It knows which bytes in a file it has to change to get to the desired state, so it doesn't have to store all of the information.