why using virtual adress space?

[mike_qnx6]

Hi Community!!!

what’s the atvantage of of the additional step, using a virtual adress space
to change the actual physical RAM locations
and therefore using an MMU?

Thank You

[rgallen]

@mike_qnx6

Hi Community!!!

what’s the atvantage of of the additional step, using a virtual adress space
to change the actual physical RAM locations
and therefore using an MMU?

Thank You

Protection.

A process with one address space, cannot damage a process with another address space.

They came up with this idea in the sixties, so it isn’t anything new.

[mike_qnx6]

Thank you rgallen!!! :mrgreen:

[mario]

Hum got me thinking, to protect processes from one another, you don’t necessarely need virtual address space, you need protected address space.

I think one advantage of virtual address space is that it leads to memory swapping. it also help debugging because each time you restart a program it will always looks like it using the same adresses.

[rgallen]

@mario

Hum got me thinking, to protect processes from one another, you don’t necessarely need virtual address space, you need protected address space.

I think one advantage of virtual address space is that it leads to memory swapping. it also help debugging because each time you restart a program it will always looks like it using the same adresses.

True. I am old enough to remember QNX2 which used the 286 protection mechanism (using selectors). The 386 virtual mechanism extended the old protection mechanism, which is why the concept of selectors remained. That said, the primary reason for VM is still protection (particularly under QNX).

Rennie