[Virtualacorn-list] !TempBin no longer works on 256MB RAM

[David J. Ruck]

On 10/01/2014 22:46, Jeremy Nicoll - ml virtualacorn wrote:
> Dynamic Areas (DAs) are, IIRC, chunks of memory, not within an app's wimp
> slot, which can be requested by an app, from the OS. In this context,
> 'dynamic' means that the both size of an area and its location in the
> overall memory map can vary from one use to the next. Unfortunately some
> apps ask for "as much as possible" and get it which then removes all the
> free RAM that other apps need, so the other apps (or the OS or the filer,
> say) then crash.  I can't quite remember why 256 MB causes such a problem,
> but it's fair to say that the code that controls how DAs work was written
> when it was pretty unusual even to have 128 MB of RAM let alone 256 MB.

It's not that they remove the actual RAM, but they take up address space.

When Dynamic Areas came in with RISC OS 3.5 to allow applications to use 
more than the 28MB maximum of the Wimpslot, the total amount of memory 
people had was still very small (tens of MB) compared to the maximum 
address space of of a 32bit processor, which is 4GB.

When you create a dynamic area you can specify both how much RAM you 
want now, and the maximum you are ever likely to need, and this much of 
the address space is reserved for it. In most cases developers thought 
"well the user may want to give it all they have", so specified -1 which 
means the how ever much RAM is in the machine. With a small amount of 
memory dozens of applications could do this without any problems.

But now with hundreds of MB of RAM fitted, specifying -1 means than only 
a couple of applications can reserve a RAM sized DA before there just 
isn't any more address space, and subsequent applications will get an 
error when they try to create Dynamic Area. That can happen even if 
there is plenty of free RAM available.

Cheers
---David
-- 
Email: druck at druck.org.uk
Phone: +44-(0)7974 108301