ReLEna - The Past Of File Archiving

Zornak · Post by **Zornak** » Mon Feb 24, 2003 4:43 pm

i have gone insane trying to figure out this thread...

i think they scare me more than i scare them

Twilkitri · Post by **Twilkitri** » Mon Feb 24, 2003 5:12 pm

According to www.filext.com, LHA is:

.LHA Compressed Archive File (LZH format; LHA.EXE)
Compressed Archive File (LHARC.EXE)
Compressed Archive File (LHARK.EXE)

Dunno what LZH is, it's probably a variant of LZ77 or LZ78.

chromus · Post by **chromus** » Tue Feb 25, 2003 12:22 am

LHA is/was an old file compression format. It doesn't compress as well as LZH or LZ77, but it's extremely easy to program, so it continues to be used.

Twilkitri · Post by **Twilkitri** » Tue Feb 25, 2003 12:24 am

Hmm? But the site said that LHAs were in LZH compression. Are they wrong, or did you type the wrong acronym again?

chromus · Post by **chromus** » Tue Feb 25, 2003 12:27 am

Not misplaced acronyms this time. LZH, the old compression algorithm, was implemented in LHA files. It's hard to keep all these compression algorithms/formats straight, with all the acronyms, so I apologize.

Twilkitri · Post by **Twilkitri** » Tue Feb 25, 2003 2:13 am

chromus wrote:LHA is/was an old file compression format. It doesn't compress as well as LZH or LZ77

chromus wrote:Not misplaced acronyms this time. LZH, the old compression algorithm, was implemented in LHA files

I'm confused...

chromus · Post by **chromus** » Wed Feb 26, 2003 1:31 am

DarkTwilkitri wrote:I'm confused...

Yeah, I tend to do that. Sorry about all the confusion, but compression algorithms/formats tend to have common acronyms with small differences. Here's a summary:

Algorithms:
LZH, LZW, LZ77

File formats:
LHA, GIF, GZ

Each file format corresponds to an algorithm, in order.

Twilkitri · Post by **Twilkitri** » Wed Feb 26, 2003 1:44 am

It's just that you say that LHA is a file format, then you say that it's a type of compression. And you say that it doesn't compress as well as LZH, then you say it uses LZH.

chromus · Post by **chromus** » Thu Feb 27, 2003 1:59 am

Admittedly, I did screw things up. Most compression algorithms have very similar names, most of which start with LZ. Let me set the record straight, ignoring all previous posts:

The initial LZ is short for Lempel Ziv, named after Abraham Lempel and Jakob Ziv, the original publishers of the algorithm. There are many variants of the algorithm. Below are some of them, along with a common file extension that uses it:

LZH: LHA
LZW: GIF
LZ77: PNG

Twilkitri · Post by **Twilkitri** » Thu Feb 27, 2003 6:32 pm

Which one is LZH based on, anyway? And do you know who the H is ?

chromus · Post by **chromus** » Thu Feb 27, 2003 9:42 pm

Well, LZ compression is a combination of run-length encoding and Huffman tree encoding. LZH, LZW, and LZ77 are all variations of the original LZ, like how to assume character frequencies and other variables. The H in LZH is named after Haruyasu, the co-creator of LZH compression. The W in LZW is named after Welch, the co-creator of LZW compression, a derivation of LZ78 compression. The problem is, LZW is patented by Unisys, so don't bother trying to use it.

LZ77 and LZ78 are named after the years they were documented.