[lug] [OT] archive formats

[Bear Giles]

Paul E Condon wrote:

>So tar is a Unix idea IMHO. It has become so embedded in the minds of
>computer people that they forget where it came from, or perhaps, they
>forget that the whole world is not Unix.
>
Every mature system has to have a way to perform backups onto streaming 
media. That's not a "unix" concept. Until recently random access backup 
media was too expensive, or not available at all, and magnetic tape, 
paper tape or even punch cards were all that was available.

Maybe I have a different perspective since I've written encoders and 
decoders for several of these formats, but under the hood they're all 
dealing with the basic problem of getting a filesystem into a stream and 
back again. There are some implementation details, but a lot of the time 
it comes down to how you look at the problem.

BTW both tar and zip are extensible, you can make them look as much like 
each other as you want, albeit at the risk of having other 
implementations chitter at you. E.g., I could easily write a 'tar' 
encoder that adds a trailing ToC like 'zip', but the standard 
implementations wouldn't understand my own extensions. Ditto per-file 
checksums or even encryption. Gnu tar did the same thing, but it's so 
widely used that it's no longer an issue since it's now the de facto 
standard.

Bear