Perhaps the most popular (or infamous) example of a shell namespace extension is the Compressed Folders extension, which handles the exploration of ZIP files. [...] Unfortunately, the code hasn’t really been updated in a while. A long while. The timestamp in the module claims it was last updated on Valentine’s Day 1998, and while I suspect there may’ve been a fix here or there since then (and one feature, extract-only Unicode filename support), it’s no secret that the code is, as Raymond Chen says: “stuck at the turn of the century.”

Unfortunately, there are degenerate cases where the ZIP Folders support really is broken. I ran across one of those yesterday. [...] Windows spent well over a minute showing “Calculating…” with no visible progress beyond the creation of a single subfolder with a single 5k file within. Huh? I knew that the ZIP engine beneath ZIP Folders wasn’t well-optimized, but I’d never seen anything this bad before. After waiting a few more minutes, another file extracted, this one 6.5 mb. This is bananas.

After some small reads from the end of the file (where the ZIP file keeps its index), the entire 11 million byte file was being read from disk a single byte at a time: