kevin@neptune.AMD.COM (Kevin Tomasek) (07/07/89)
I hope this subject hasn't been beat to death before, I haven't seen it mentioned... 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. It didn't have a problem... When I restored the files, C source files, they appeared to just fine. They all compiled correctly and ran. These same floppies would format to about 700kb in the switchless format mode but not so reliably. I tried this again with even more data and the software said that it had loaded 1.5Mb before asking for another disk. Does the fastback software have some super format coding scheme that allows it to apparently backup this muck information?? Should I not believe it knowing the floppies aren't rated for 1.2Mb. any info... thanks. -- ************************************************************************* Kevin Tomasek kevin@neptune.amd.com AMD - Advanced Micro Devices, Austin, Tx (512)462-5381 *************************************************************************
kleonard@gvlv2.GVL.Unisys.COM (Ken Leonard) (07/10/89)
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 Leonardleonard@bucket.UUCP (Leonard Erickson) (07/11/89)
Fastback got around 400k on a disk by formatting 10 sectors per track. It crammed even more data on by running the data thru some sort of compression algorithm. Fastback Plus uses DOS formatted disk and makes the compression switchable (takes more disks, but less time with it off). -- Leonard Erickson ...!tektronix!reed!percival!bucket!leonard CIS: [70465,203] "I'm all in favor of keeping dangerous weapons out of the hands of fools. Let's start with typewriters." -- Solomon Short