Restriction on no. of processes under Windows CE

Restriction on no. of processes under Windows CE

Post by Emil Roja » Fri, 23 Apr 1999 04:00:00




> Hi

> I wished to know why is there a restriction on the no. of processes in Windows
> CE ( max. of 16 in Windows CE 2.0 ) and by doing so will the real time
> capabilities of the OS be affected ( enhanced or deteriorated ).

I think the number is 32, but it could be 16.

The number of processes are limited but not the number of threads.
The details are foggy right now, but CE isolates (protects) processes
from each other by using the MMU, i.e. the address are virtual.
To make their job easy, and presumably efficient, they simply divide the
address space in 32 equal chunks giving each process 1/32 of the
address space.

Some of  you will have all ready noticed the implied limitation
to a 128K address space/process.  Certainly not a problem for
a handheld device today.

Quote:

> In pSOS ( another RTOS ), the max. no. of processes  is not limited though
> there is a concept of max. no. of active processes.

pSOS does not support a process model or a VM.  So in effect Win/CE can support
32 pSOS like applications at the same time.  There is a small matter of
performance,
but I'll let others rail against the evil monster lurking in the rain forest.

There are other RTOSs that do support a process model and do not limit the
number.

emil

 
 
 

Restriction on no. of processes under Windows CE

Post by Scott Johnso » Sat, 24 Apr 1999 04:00:00




> > Hi

> > I wished to know why is there a restriction on the no. of processes in Windows
> > CE ( max. of 16 in Windows CE 2.0 ) and by doing so will the real time
> > capabilities of the OS be affected ( enhanced or deteriorated ).

> I think the number is 32, but it could be 16.

> The number of processes are limited but not the number of threads.
> The details are foggy right now, but CE isolates (protects) processes
> from each other by using the MMU, i.e. the address are virtual.
> To make their job easy, and presumably efficient, they simply divide the
> address space in 32 equal chunks giving each process 1/32 of the
> address space.

Something like that, though I think one of these segments is always
aliased to the memory segment of the current process.

Quote:> Some of  you will have all ready noticed the implied limitation
> to a 128K address space/process.  Certainly not a problem for
> a handheld device today.

I assume you mean 128Mb.  A limitation of 128Kb would be a problem...
:)

It might be 64Mb, though, because isn't the upper 2Gb of the address
space reserved for the kernel?  Or am I thinking of other MS
operating systems?

Quote:> > In pSOS ( another RTOS ), the max. no. of processes  is not limited > > though there is a concept of max. no. of active processes.
> pSOS does not support a process model or a VM.  So in effect Win/CE
> can support 32 pSOS like applications at the same time.  There is a
> small matter of performance,

Not a small matter at all...

Quote:> but I'll let others rail against the evil monster lurking in the rain > forest.

At least as of 2.x, it is QUITE a stretch to call WinCE an RTOS,
despite MS marketing to the contrary.  WinCE might be appropriate
for soft real time applications, but it was primarily designed for
low-power, low-memory consumer devices.  Not for embedded systems.

MS keeps indicating that 3.x will be more realtime.  As I haven't
seen it, I can't comment...

Quote:> There are other RTOSs that do support a process model and do not limit > the number.

QNX and LynxOS come to mind as two examples...

Scott

--
========================================================================
Scott Johnson          Patriot, Beer-Drinker, Geek            GO BLAZERS
Don't take yourself too seriously.  Nobody else does.........
========================================================================

 
 
 

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