Subj : docs/zmodem_comparison.md
To   : Git commit to main/sbbs/master
From : Rob Swindell (on Debian Linux)
Date : Sun Aug 30 2026 23:50:56

https://gitlab.synchro.net/main/sbbs/-/commit/0822029d905accebd45d3265
Modified Files:
	docs/zmodem_comparison.md
Log Message:
docs/zmodem: measure what MobyTurbo is worth

Rob asked what sexyz would gain by supporting MobyTurbo.  zmtx/zmrx 2.05
implements it, so it can be measured rather than estimated.

It is worth about 2.3% on compressed or otherwise incompressible data and
essentially nothing on text.  ZMODEM must escape seven byte values --
ZDLE, 0x10, 0x11, 0x13, 0x90, 0x91 and 0x93 -- at one extra wire byte
each, which is 7/256 = 2.73% of uniformly distributed data; MobyTurbo
drops that escaping on links known to be transparent and recovers exactly
it.  Measured on 1 MiB: random data goes from +2.84% overhead to +0.49%,
while text goes from +0.09% to +0.09%.  The split is the escape rate
itself -- those seven values occupy 2.746% of the random file and 0.000%
of the text one, none of them occurring in ordinary ASCII.

Three bounds on what that is worth, all recorded: it is a wire saving, so
it converts to throughput only where bandwidth binds rather than in this
document's CPU-bound regime; it needs a transparent link, the same
precondition ESC8 exists to work around, inverted; and it is negotiated
by the receiver, so DSZ sz -m to sexyz puts exactly the same bytes on the
wire as without it.

Forsberg measured about the same himself.  DSZ.DOC's benchmark table has
Pro-YAM at 231 cps standard against 237 with MobyTurbo on a 2400 bps
link, +2.6%, within half a point of the figure here thirty-six years
later.

Also adds feature-table rows for MobyTurbo and Pack-7, both of which
zmtx/zmrx 2.05 now implements and neither sexyz nor lrzsz does.
--- SBBSecho 3.37-Linux
 * Origin: Vertrauen - [vert/cvs/bbs].synchro.net (1:103/705)

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