On Tue, Aug 26, 2008 at 4:34 PM, Lukas Beeler
<lukas.beeler@xxxxxxxxxxxxxxxx> wrote:
Just like on every other modern operating system - including Unix.
Each process on Unix, Windows has it's own address space.
Heck, without address space separation, security would be nonexistant
- just like in the times of DOS.
Nonsense....
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.
Dr. Soltis' books, "Fortress Rochester" and the older "Inside the
AS/400", provide some details about why a shared memory model was
chosen and it's advantages over seperate address spaces.
Basically, one key thing is that the seperate address space model came
out of "time-share" systems. In such a system, it makes perfect sense
for a process being run for Company A be completely seperate from a
process being run for Company B. On the other hand, when you've
talking about two processes being run by Company A on an internal
computer system, having a hard division between the processes doesn't
make sense as it makes it difficult to share information (objects)
between the processes.
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.
HTH,
Charles Wilt
midrange.com
