Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!iuvax!cica!tut.cis.ohio-state.edu!cwjcc!gatech!udel!burdvax!gvlv2!kleonard
From: kleonard@gvlv2.GVL.Unisys.COM (Ken Leonard)
Newsgroups: comp.sys.ibm.pc
Subject: Re: fastback, 1.2m floppies
Keywords: fastback, 1.2m floppies
Message-ID: <267@gvlv2.GVL.Unisys.COM>
Date: 10 Jul 89 13:27:02 GMT
References: <1027@neptune.AMD.COM>
Distribution: usa
Organization: Unisys Defense Systems, NISD, Great Valley Laboratory
Lines: 36

In article <1027@neptune.AMD.COM> kevin@neptune.AMD.COM (Kevin Tomasek) writes:
* The software fastback formats and backs up info onto the floppy of
* choice.  Trying to find out some of its error checking abilities I put
* in a 360kb size floppy and told it to  store much more than 260kb.
* As it turned out the size of the files to backup were about 1.1M.
* ...
* These same floppies would format to about 700kb in the switchless format
* ...
* I tried this again with even more data and the software said that it had
* loaded 1.5Mb before asking for another disk.
Kevin doesn't say _which_ version/level of Fastback he has, but...
Fastback does at least two things in its recording which the user may or
may not be able to set and/or see, depending on the version/level:
--1) Data Compression:  cramming umpteen bytes as read from original file
----before even thinking about writing to disk.  Has been known to achieve
----a ratio as high as several-to-one for some files (especially things
----like well-written source code with lots of white space, etc.)  So the
----original approx MegaByte of "C" may well get down to 1/2 or 1/3
----MegaByte of stuff to be written.
--2) Forward Error Correction:  writing extra information along with the
----basic information.  Which (as a _GROSS_ oversimplification) lets you
----read back with some number of bit errors and then reconstruct the
----basic information by using the extra information.  The last time I
----looked, FB was using about 20% extra bits in its "safest" mode--which
----means that it could read back with almost 10% raw bit errors and still
----reconstruct the original data.
****
So, If 1MB source file compresses to 300K, then gets recorded as 360K, you
can end up seeing 1MB on a 360K-type floppy _either_ at real-360K mode
_or_ at 30% usable sectors with forced-1.2M mode :).
****
What's really nice is having a real 1.2M floppy hold 3MB of source code or
text files!
-----------
Regardz,
Ken Leonard