Virtual Memory????

I am doing a project for my operating systems class and I want to use QNX 4
but I am not sure if I can disable the virtual memory. I need to disable
it to do some comparisons between system operation with and without. Any
help on the subject would be greatly appreciated. Thanks in advance.

Ross Brantner
Shippensburg University, PA

You can’t disable it. It’s built in the system.

However if you use QNX6 you have control over swapping ( QNX4
doesn’t have swapping)


“Ross Brantner” <brantner@innernet.net> wrote in message
news:8tqkqm$o2a$1@inn.qnx.com

I am doing a project for my operating systems class and I want to use QNX
4
but I am not sure if I can disable the virtual memory. I need to disable
it to do some comparisons between system operation with and without. Any
help on the subject would be greatly appreciated. Thanks in advance.

Ross Brantner
Shippensburg University, PA

can you define what “virtual memory” means in your class? Qnx 4.xx doesn’t use virtual memory like Ms products use (swap file) but we do use virtual addressing via the hardware mmu. The addresses that a program uses are all ‘virtual addresses’ not physical addressing.

The free version of Qnx ( the Qnx Realtime Platform) has a virtual memory (paging to harddisk) but you have to enable it in your program its not on by default.

Previously, Ross Brantner wrote in qdn.public.qnx4, comp.os.qnx, qdn.public.qnx4.photon, qdn.public.qnx4.devtools:
{ I am doing a project for my operating systems class and I want to use QNX 4
{ but I am not sure if I can disable the virtual memory. I need to disable
{ it to do some comparisons between system operation with and without. Any
{ help on the subject would be greatly appreciated. Thanks in advance.
{
{ Ross Brantner
{ Shippensburg University, PA
{


Pat Ford email: pford@qnx.com
QNX Software Systems, Ltd. WWW: http://www.qnx.com
(613) 591-0931 (voice) mail: 175 Terence Matthews
(613) 591-3579 (fax) Kanata, Ontario, Canada K2M 1W8

Hi Ross,

When you are referring to virtual memory are you thinking about it in the fashon
that Windows does? (swap files)? If thats the case QNX4 does not have any swap files
for memory.

Erick

In qdn.public.qnx4 Ross Brantner <brantner@innernet.net> wrote:

I am doing a project for my operating systems class and I want to use QNX 4
but I am not sure if I can disable the virtual memory. I need to disable
it to do some comparisons between system operation with and without. Any
help on the subject would be greatly appreciated. Thanks in advance.

Ross Brantner
Shippensburg University, PA

In qdn.public.qnx4 Ross Brantner <brantner@innernet.net> wrote:

I am doing a project for my operating systems class and I want to use QNX 4
but I am not sure if I can disable the virtual memory. I need to disable
it to do some comparisons between system operation with and without. Any
help on the subject would be greatly appreciated. Thanks in advance.

What do you mean by virtual memory? QNX 4 does not implement any kind of
page or swap to disk – everything is always RAM resident. But, QNX4 does
use virtual addressing – program’s addresses do not map 1to1 with physical
addresses, but in fact get looked up through page tables/MMU inside Proc32
to map a virtual address to a physical address. This can not be disabled.

If you are thinking of what “sin in” reports as “Virtual” – that is really
only information about how many page table entries have been allocated by
Proc32 and how many are currently unused (used) – it does not refer to
any sort of page or swap to disk.

-David