Comment by jleahy
5 years ago
There's a very good chance that a single bad bit in a 10 GB Windows game will prevent it from loading.
The average game might contain a multi-megabyte executable along with gigabytes of assets. Those assets will be stored in some kind of compressed format (for example Quake III used 'pk3' files, which were actually zips). These compressed files with inevitably have checksums, and an invalid checksum will prevent them from loading.
Yup, that's why most physical medium have some form of ECC or FEC[1].
[1] https://en.wikipedia.org/wiki/Reed%E2%80%93Solomon_error_cor...
You’re assuming the game engine will panic on a bit error loading what’s probably a texture or model mesh. This probably isn’t the case for most games, especially release builds. You might get a console message.
A 1-bit error in a compressed file will cause every subsequent bit in the entire file to end up wrong (well, 50% of them), and probably the file length to end up wrong, and probably the decompression state machine to get stuck and confused. This is why basically all compressed formats carry a CRC (eg. zip, gz, xz).
Most games don’t store their assets in a single one-shot-load pack file anymore. They use chunked asset files where individual assets or packs will be compressed and then concatenated with a master index, meaning you don’t have to load the whole file when the engine needs only a subset. This means the checksums necessarily cannot cover the entire data file, because then you would need to read the entire file to verify a single asset anyway, throwing away the benefits of random access. You can also turn the checksums off for “speed,” and some do.
If you have something like a Deflate stream, there is a chance that the flipped bit will affect a symbol but change it into a symbol with the same length. Could do anything from changing a single byte in the output, to changing bytes in a bounded range, to corrupting the entire rest of the stream, or making it fail to decompress (not every deflate stream is valid, far from it).