[CoCo] 720kb vs 1.4mb 3.5" disks

[KnudsenMJ at aol.com]

In a message dated 12/12/03 10:01:25 PM Eastern Standard Time, wb8tyw at qsl.net 
writes:

> Most of the issues come from operating systems deferring updates to the 
>  disk from having large file cache memory.
>  The COCO does not have lots of memory to buffer up I/O, so it is less 
>  likely to have a power interruption at a critical time that would leave 
>  orphaned space.

Funny -- Coco's small RAM became a virtue here.  But ISTR that OS-9 and OS-K 
have a deliberate design philosophy of no such write deferrals, so power 
losses and other crashes cannot trash the file system or even one file (unless it 
was being written at the moment).  The price, of course, is the slow disk 
writing we all suffer thru under OS-9 -- I think it writes one sector, updates the 
FAT, writes another, hits another FAT bit, etc.  But very safe.

>  If there is not a utility to check the integrity of the OS-9 file 
>  system, then there should be.

There's a stock one under OS-K, but ask me its name and I'll flash my AARP 
card.  It collects orphaned sectors, catches sectors allocated to more than one 
file (bad!), etc.  Maybe it's called DCHECK, same as in DOS.  And ISTR there's 
a watered-down version under OS-9 too.
  
>  The only issue I ever heard about that is long term storage of the 
>  floppies with the heads clamped down was bad.

It's physically the same issue.  Early Tandy drives had no head-load 
solenoid, so the head was clamped against the disk all the time that the lever was 
clamped over.  That would put a "dimple" in your diskette.

  Later drives only load the head against the surface when the solenoid is 
energized by the driver software, and your drive can be set to unload the head 
when the disk is not doing I/O.  Power failure causes the head to retract -- 
hopefully *before* any glitches get to the heads.

Newer hardware seems to be more forgiving.  --Mike K.