Compression vs Speed

Jay

Compression on roms.

Just wondering if there is any advantage to having your roms compressed or uncompressed?
Obviously compressed saves space, but does this mean they have to be decompressed to load or take longer?

If it speeds things up i am willing to use more space.

Also noticed the some roms will not load on certain emulators even though it is supported, for example PSX, i have files in .7z, but they will not run unless uncompressed or recompressed to .zip, even though it says supported.

I have tried both and it seems a little faster when not compressed to me.

caiot5

I know it is an old thread, but I was wondering the same and have not yet found the answer.
Does anyone knows anything in that regard?

joinski

caiot5

Why not just try it out and see if there are differences in loading times between compressed and uncompressed?
My guess is, that it depends on the system and/or rom size. And of course the type of drive you are using for the roms (old/slow usb 2.0 thumb drive vs SSD for example). And maybe the power of the hardware, you are using (RPi vs. high end x86 PC).
But that are just guesses. Better try yourself and then you will see what happens.

Atari

Disc-based systems do not support computer compression formats like zip or 7z (in fact, they never did, I’m curious as to where the OP got this contrary information from?)

For those, you would use CHD or compress the image itself (iso is a format which isn’t strictly a single type of format).

In general, there is no (noticeable) performance loss for using compression. It’s a no-brainer to use. The biggest downside is that you have to add an additional step for preparing your ROMs to be added into your userdata.

jul059

I found it made no significant difference, although I think there is a theoretical one (slower startup for roms, longer load times for disc-based).

.7z for all roms for which you will use retroarch emulators. don’t use ppmd or bzip2, those algorithms could make games load noticeably slower. Try this to batch-optimize your files: Ultra7z optimizer
.zip for most other roms unless a specific emulator is picky and doesn’t support compression.
.chd for PS1, saturn, dreamcast, PC-Engine CD, Sega CD, 3DO, probably others. Use CHDMan
.cso for PS2, PSP. Use maxcso for maximum compression, with a command line that looks a bit like this: maxcso --threads=8 --use-zopfli --use-7zdeflate --no-lz4 --no-lz4brute and adjust threads according to your cpu.
.rvz for gamecube and Wii. Use the latest Dolphin emulator to compress.
.wua for WiiU, use the latest cemu emulator to compress.

I also like to use pinga in lossless mode on all PNG files once everything is setup and scraped. It’s a pretty fast lossless png optimizer, works in batch mode.