[jandrese]

Yet for the same compatibility reasons most people stuck with .jpg and .htm, at least in the Windows world. Even now it's very unusual to see a .jpeg extension on a filename.

The metadata that Macs kept in the resource fork go way beyond file type and creator too. It included things like the file's Icon, creation/modification information (so it would survive a trip over the Internet!), loads of stuff for applications (menus, graphics, sounds, etc...), formatting for plain text documents (so they fall back to plain text on unsupported systems), and so much more.

Fun fact: NTFS supports the concept of a resource fork on files, but almost nothing in Windows uses it. I think I've seen more malware hiding stuff in there than legitimate uses in the wild. Worse, even the obvious case of loading a Mac file on a Windows machine it usually fails and falls back to creating the clunky separate directory instead.

[dfox]

NTFS does not have resource fork in the MacOS sense nor extended attributes in the unix sense. Instead it allows for file to have multiple named contents that are accessible by same file IO API (in essence the file can behave like a simplified directory). There is no distinction between data and metadata stored this way. In the late 90s MS even intended to not use OLE compound storage fileformat (ie. what office 97/2000 formats are built on) on NTFS drives and instead write the objects into separate streams (reportedly it was not implemented because then windows would have to somehow transparently reconstruct the compound storage when you copy such file to non-NTFS drive or upload it to the internet). Today apart from malvare hidding only major usage multiple streams have are the "this file was downloaded from internet, are you sure you want to open it?" prompts which store the internet-ness of file in secondary stream.

[jandrese]

Conceptually the MacOS Resource Fork is basically a directory where all of your filenames have to be exactly 4 characters long. The only difference is that each "file" might be a stack of "files". So you might have a CODE resource that has multiple CODE segments in it.

One thing I loved about old MacOS apps is opening them up in ResEdit and so much of how the thing was built.

[duskwuff]

> Conceptually the MacOS Resource Fork is basically a directory where all of your filenames have to be exactly 4 characters long. The only difference is that each "file" might be a stack of "files". So you might have a CODE resource that has multiple CODE segments in it.

Sort of. It would be more accurate to say that each filename was a 4-letter type code and a 16-bit ID. Each resource could also have a name, but that was less frequently used (and didn't have to be present, let alone unique).

More importantly, resource forks didn't exist in isolation. They were loaded into a chain of active resource files -- for instance, while working with a Hypercard stack, the resource chain would include the active stack, the Home stack, the Hypercard application, and the System suitcase. A stack could use resources (like icons or sounds) from any of those sources.

[hypervis0r]

You don't see .jpeg because people are used to .jpg. There's nothing incompatible with long names that we care about.

Also, that Windows feature you mention is called ADS - alternate data stream.

[jandrese]

Yes, but you also never see extensions like:

.jpeg.photoshop.ro.creat127339292....

The filename extension is the bare minimum of metadata for a file and not easy to extend.

Even then Unix systems will skip even that minimal metadata and force you to messily search for magic numbers at the start of the file and make a guess.