> To this day I still use .7z and merged sets for all my release set ROMs. I've never > needed to perform any operations on them that are noticeably slower.
I don’t know how you can say that with a straight face. Pretty much everything is slower with 7zip archives:
LZMA compression itself is slow, so creating or adding to an archive is slow. You do plenty of this if you’re adding sets, replacing bad dumps, and so on.
LZMA decompression is slow (which has inspired development of algorithms like zstandard that give better decompression performance). This gives a speed penalty when loading a machine.
Solid archive compression means MAME ends up repeatedly decompressing data as it loads ROMs to retrieve files members within solid blocks. The caching the LZMA SDK uses isn’t very effective because MAME doesn’t always read archive members in the order they appear in the file. This affects every launch in MAME if the ROM set contains more than a couple of files.
Solid archive compression means that removing or replacing members in an archive requires recompressing unaffected members, whereas with a PKzip archive the unaffected members can simply be copied and the central directory rewritten. You do this any time you reorganise clones, move ROMs to devices, replace bad dumps, and so on.
All of this is measurable and noticeable. You might think the small space saving justifies it, but many others don’t.
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