Back to home page

DOS ain't dead

Forum index page

Log in | Register

Back to the forum
Board view  Mix view

Heatshrink compressed drives? - Tamp ISO compression test (Announce)

posted by jadoxa Homepage E-mail, Queensland, Australia, 31.01.2025, 09:24

> I fail to see where the total number of
> sectors in the image is stored, though?

I didn't, as I thought the driver tested that, but turns out it just uses the file size. That would mean either moving the offsets to the end, adding a pointer to that, then testing EOF; or store the number of sectors and test it; or leave it and hope. :)

> I am curious about the distribution of compressed sector sizes for typical ISOs

As tom said (it doesn't matter what I have, it matters what you have). Having said that, I did another test with LZ4 and here's what I got.


                    LZ4        Tamp        LZ4         gzip
                Ratio %     Ratio %     Ratio %     Ratio %
250GAMES        1.36  73.4  1.41  70.8  1.51  66.2  1.61  62.3
APC4101         1.03  97    1.03  96.9  1.05  95.4  1.06  94.7
EXTREME         1.49  67.2  1.68  59.6  1.8   55.6  2.09  47.9
fdosgame135b    1.69  59.3  1.81  55.1  2.01  49.7  2.25  44.4
FUZZYCD         1.18  84.8  1.22  81.9  1.43  70.2  1.45  69.1
Holmes2         1.13  88.2  1.19  83.7  1.3   76.7  1.42  70.5
NFSPCCD         1.12  89.6  1.14  87.7  1.16  85.8  1.24  80.4
osborne         1.62  61.6  1.7   58.7  1.94  51.6  2.11  47.5
PCU_OCT99_1     1.06  94.7  1.06  94.4  1.08  92.9  1.08  92.2
PCU_OCT99_2     1.01  99.2  1.01  99    1.01  98.5  1.02  98.2
PCW             1.29  77.7  1.44  69.5  1.55  64.3  1.77  56.5
RTZ-CD          1.1   91    1.15  86.7  1.33  75    1.44  69.5
Stellar7        1.08  92.8  1.13  88.3  1.14  87.4  1.3   76.7
Titus           1.13  88.1  1.16  86.3  1.2   83.6  1.24  80.8


APC, PCU & PCW are magazine cover discs; osborne is from my first PC (PC-DOS 6.3 & WfWg 3.11); the rest are games.
LZ4 (1.10.0) & Tamp are sector compression, the other LZ4 (1.3b) & gzip are file; ratio is the size of the original compared to the compressed (original_size / compressed_size); % is the opposite (compressed_size / original_size * 100).

Whilst LZ4 did save half a gig, and Tamp another 100 meg on top of that, I still don't think it's worth the effort.

> A simple scheme would be to only store the absolute offset of every 16th
> compressed sector, followed by only the 16 lower bits for the next 15
> offsets.

A less simple scheme that saves even more would be to store only the length, allowing packing two sectors into three bytes (a la FAT12); doing that for 32 sectors would be 52 bytes (dword address plus 48 bytes for the 32 lengths). Not sure how practical it would end up being, though.

 

Complete thread:

Back to the forum
Board view  Mix view
22208 Postings in 2050 Threads, 396 registered users, 112 users online (0 registered, 112 guests)
DOS ain't dead | Admin contact
RSS Feed
powered by my little forum