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

posted by mceric, Germany, 31.01.2025, 15:15

Hi! Thank you for sharing your results :-)

Let me sort those by TAMP ratio, omitting the magazine CD which did not compress well (saving less than 8% except for PCW), leaving the games and your Osborne (DOS/WfW) data, and expressing the percentages in saved instead of remaining percent:


.                  LZ4        Tamp           LZ4         gzip
.               Ratio %     Ratio %        Ratio %     Ratio %
fdosgame135b    1.69  40.7  1.81  44.9     2.01  50.3  2.25  55.6
osborne         1.62  38.4  1.70  41.3     1.94  48.4  2.11  52.5
EXTREME         1.49  32.8  1.68  40.4     1.80  44.4  2.09  52.1
250GAMES        1.36  26.6  1.41  29.2     1.51  33.8  1.61  37.7
FUZZYCD         1.18  15.2  1.22  18.1     1.43  29.8  1.45  30.9
Holmes2         1.13  11.8  1.19  16.3     1.30  23.3  1.42  29.5
Titus           1.13  11.9  1.16  13.7     1.20  16.4  1.24  19.2
NFSPCCD         1.12  10.4  1.14  12.3     1.16  14.2  1.24  19.6
RTZ-CD          1.10   9.0  1.15  13.3     1.33  25.0  1.44  30.5
Stellar7        1.08   7.2  1.13  11.7     1.14  12.6  1.30  23.3


If I understand you correctly, the left 2 columns are per-sector compressed, the right are whole-ISO solid compression? And TAMP always compressed better than LZ4? :-)

One could say that solid compression typically only squeezes out an extra 10%.

GZIP usually does not compress your ISOs much better than the faster LZ4.

Note that TAMP is fast in decompression, which is important for the use in compressed disk images, but slow in compression, while ZLIB is balanced there.

> > 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.

My idea was to avoid having to run a loop of additions to reconstruct the offset of an arbitary sector.

By storing only the lengths, you would need a loop. However, you could force all lengths and offsets to be multiples of 8 or 16, to be able to encode the compressed length of a 2k or 4k sector in a single byte.

---
FreeDOS / DOSEMU2 / ...

 

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