Hi Eric,

I expect that in the next few years we'll see very large hard drives and 
they will continue to support 512 byte sector sizes - that is what the 
system manufacturers demand.  The actual sector size of the drive might 
be 4KB but the drive will allow the host to choose a 512 byte or 4KB 
sector format and adjust accordingly.  If 512 byte sectors are chosen 
and the drive is truly using 4KB it will do the proper read/modify/write 
sequence for writing random 512 byte blocks.  For reads and sequential 
writes the performance impact will be negligible.  Random writes present 
the biggest challenge - better drives will be able to minimize the 
performance impact.  Most of us run with write caching enabled which 
also helps the performance problem that random writes cause.

 From an operating system point of view things are more complicated.  
The classic partitoning scheme doesn't work well on giant drives.  You 
are better versed in the newer partition table schemes than I am.  We 
might just have to live within the limits of a 2TB device if we don't 
want to fix the problem.  I think I can live in 2TB for my DOS systems ...

In the early days of DOS device drivers often had to deal with sector 
sizes that were not 512 bytes.  I have an Iomega Bernoulli Box A220 (2 
8" cartridges holding 20MB each) that uses 256 byte sectors, and the 
device driver is responsible for dealing with that.  I think even the 
later Adaptec ASPI drivers know how to work with SCSI devices that 
report 256 byte sectors.

If we ever have to deal with this issue in the kernel I would be 
inclined to continue to use a 512 byte sector size within the OS and 
hide any differences at the lowest levels.  This might not be as 
efficient as supporting different sector sizes natively but that 
probably becomes too complicated and error-prone.  There is a lot of 
code that assumes 512 byte sector sizes and it is not worth disturbing it.

I'm going to get flamed for this but I'm not too worried about the 
performance hit that translation layers cause.  FreeDOS is *insanely* 
mismatched for modern hardware, and there is plenty of performance 
overhead available to dip into.  Anybody who really needs the speed 
should step up to a more modern operating system.  We're not making use 
of the hardware we have already and we're probably a decade or two late 
in trying to keep up with advances in hardware.


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