Backups [was Re: Is tape dead?]

[Fred Cisin]

On Sun, 20 Sep 2015, Jon Elson wrote:
> Well, one would assume this is also OS specific.  I would guess it would be 
> incredibly hard to make a "disk" virus that would work on greatly differing 
> OS's like Linux AND Windows.  No telling what would happen if one of these 
> disk viruses got onto a hard drive on a Windows system and then the drive was 
> reformatted and loaded with Linux.
> Most likely you'd have odd crashes or something.

It is possible to create an executable file that identifies the OS that it 
is running on and does a conditional jump to different code, assuming that 
the processor uses the same instruction set.

How different the OS's are would determine how much code could be shared. 
If they are very different, then the executable file could be twice as 
large, with no code in common.


It is even possible to make a disk that is readable as multiple disk 
formats, so long as each is expecting the DIRectory tracks to be in 
different places.
One of the many projects that I never got ready for market was to make a 
multi-platform distribution format for software.  "Save a few cents on 
media costs by putting all of your platforms on one disk"  But, after 
August 1981, it eventually became apparent that the need for such was not 
going to be around much longer.

If the boot code is short enough, it is even possible to have an FM, an 
MFM, and a GCR boot sector in the same boot track, since each will not 
even see any except its own.  Formatting/recording a track with mixed 
densities and/or encodings and multiple sector sizes is not a supported 
function in most operating systems, nor even FDCs, but can be done with 
some flux transition controllers.