Basil Fernie wrote:

  > Nice bit of history, makes your point clear. But my point is, now, 
how does
> swapper.dat actually work? Does it still receive data temporarily from
> physical RAM - or a clearly defined and limited portion thereof - if that's
> inadequate for the moment? If not, then "swapper.dat" is
truly redundant,
> obsolete and unnecessary, except for those of us who are still running OS/2
> on something like the 16MHz 386SX I started using it on, with indeed 4MB of
> RAM. So it should have no place in, for example, eCS1.1 But if it has *any*
> functionality on a reasonably current PC, then I would expect that
> functionality to address at least the situation where a limited section of
> RAM, specifically the cache (which for those of us not using hpfs386 is
> limited to 2MB, not very much, right?, and even hpfs386 has a fairly modest
> limit) overflows. Does it just stop caching, or does it shift its overload
> out onto swapper.dat? If it does, where would you rather have swapper.dat
> sitting? On a physical HDU, or in RAM on a virtual drive? Does that make my
> point clear?

I've running here an eCS 1.1 with 512 MB RAM - and it is possible to 
get a swapper of 1 GB in size depending on the actions I do with the 
system. You would need 4 GB RAM inserted into the mashine to get 
OS2/eCS out of address space without swapping.

That is because OS2/eCS is designed to use of up to 4GB virtual 
address space whereas any 4KB not really available in RAM gots into 
swapper.dat when there is more need of RAM than available.

> So I think the core issue probably is actually, do you have enough RAM to
> dispense totally with *caching*? (And does your software co-operate by not
> off-loading itself from RAM while not active, *and* does your OS permit this
> state...) If so, it makes no sense to have swapper.dat residing in RAM, but
> I would certainly still want to retain a capability for a HDU swap-file just
> in case; happy in the knowledge that it would never (hardly ever?) be used,
> and surely wouldn't be impacting overall system performance just by being
> available.

swapper.dat is to extend RAM. Using a portion of RAM to have swapper 
in it is as if you tries to put a bag into your bag to have another 
bag to fill. This results only that you gets significantly less room 
to store something.

> Any gurus on hpfs caching policies to enlighten us are welcome to comment.

You would use JFS instead of HPFS now because
- JFS volumes can be bigger than HPFS ones
- JFS can contain single files bigger than 2GB
- JFS can use a bigger ortion of RAM to cache disk accesses
- JFS can extend an full volume on another logical or physical drive 
on the fly when you asks LVM for.


 
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