Re: What should I say to a *nix community?

["Lukas Beeler" <lukas.beeler@xxxxxxxxxxxxxxxx>]

On Wed, Aug 27, 2008 at 2:47 PM, Charles Wilt <charles.wilt@xxxxxxxxx> wrote:
> The IBM i uses a shared address space, I think you'd be hard pressed
> to prove that security is nonexistant because of it.  In fact, the
> reverse is more likely to be proven.

Processes are still isolated from each other, and can't read or write
the memory of other processes.

The way this is exactly implemented technically does not matter.

DOS, on the other hand, had one single address space where every
running program could modify every single bit of it. More or less.

> In addition, there's a huge performance penalty to having seperate
> address spaces for each process.  It takes considerable effort to
> restore/save the address space during context switches by the
> processor, 1000s of CPU instructions is not uncommon.  With a shared
> address space, it's basically a single GOTO instruction.

When emulated, yes. That's why every modern platform has an MMU.

http://en.wikipedia.org/wiki/Memory_management_unit