Memory administration

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Christian G. Charette

Memory administration

Post by Christian G. Charette » Thu Oct 30, 2003 2:56 pm

Hi,

im migrating to QNX 6 and I see that there is again some sort of virtual
memory.... I'd like to know how the OS works with this memory and mantain
the realtime capabilities.
Thanks in advance, and sorry for my english.

Christian.-

Chris McKillop

Re: Memory administration

Post by Chris McKillop » Thu Oct 30, 2003 5:27 pm

Christian G. Charette <cgcharette@argencard.com.ar> wrote:
Hi,

im migrating to QNX 6 and I see that there is again some sort of virtual
memory.... I'd like to know how the OS works with this memory and mantain
the realtime capabilities.
Thanks in advance, and sorry for my english.
Only the x86 kernel has any possibility of paging to disk today, and it isn't
a supported feature. It is only there to allow the GNU toolchain (gcc, etc)
to be able to run. Applications have to enable this behavior, it doesn't
do it by default.

chris

--
Chris McKillop <cdm@qnx.com> "The faster I go, the behinder I get."
Software Engineer, QSSL -- Lewis Carroll --
http://qnx.wox.org/

David Gibbs

Re: Memory administration

Post by David Gibbs » Thu Oct 30, 2003 10:42 pm

Christian G. Charette <cgcharette@argencard.com.ar> wrote:
Hi,

im migrating to QNX 6 and I see that there is again some sort of virtual
memory.... I'd like to know how the OS works with this memory and mantain
the realtime capabilities.
Thanks in advance, and sorry for my english.
Virtual memory is not the same as page/swap to disk.

Basically, we use MMU hardware to supply protected virtual address
spaces to processes -- but all processes are always resident in
RAM. So, virtual memory is, essentially, only used as a translation
for physical addresses.

-David
--
QNX Training Services
http://www.qnx.com/support/training/
Please followup in this newsgroup if you have further questions.

Robert Krten

Re: Memory administration

Post by Robert Krten » Thu Oct 30, 2003 11:07 pm

David Gibbs <dagibbs@qnx.com> wrote:
Christian G. Charette <cgcharette@argencard.com.ar> wrote:
Hi,

im migrating to QNX 6 and I see that there is again some sort of virtual
memory.... I'd like to know how the OS works with this memory and mantain
the realtime capabilities.
Thanks in advance, and sorry for my english.

Virtual memory is not the same as page/swap to disk.

Basically, we use MMU hardware to supply protected virtual address
spaces to processes -- but all processes are always resident in
RAM. So, virtual memory is, essentially, only used as a translation
for physical addresses.
I'm going to be pedantic :-)

Virtual address == translation of process address to physical address
Virtual memory == swapping / paging to secondary storage.

When using the terms, decide what is "virtual" about the noun; in the
case of the address, it's a virtual address 'cuz it's not a real,
physical address. In the case of virtual memory, the memory is virtual,
meaning that it's not really there (and hence is "faked" by paging).

Sorry, just one of my buttons :-)

Cheers,
-RK

--
[If replying via email, you'll need to click on the URL that's emailed to you
afterwards to forward the email to me -- spam filters and all that]
Robert Krten, PDP minicomputer collector http://www.parse.com/~pdp8/

Christian G. Charette

Re: Memory administration

Post by Christian G. Charette » Fri Oct 31, 2003 1:49 pm

Thanks to all!!!!, that's just the explanation I was needing..

"Robert Krten" <rk@parse.com> escribió en el mensaje
news:bns5j8$n3c$1@inn.qnx.com...
David Gibbs <dagibbs@qnx.com> wrote:
Christian G. Charette <cgcharette@argencard.com.ar> wrote:
Hi,

im migrating to QNX 6 and I see that there is again some sort of
virtual
memory.... I'd like to know how the OS works with this memory and
mantain
the realtime capabilities.
Thanks in advance, and sorry for my english.

Virtual memory is not the same as page/swap to disk.

Basically, we use MMU hardware to supply protected virtual address
spaces to processes -- but all processes are always resident in
RAM. So, virtual memory is, essentially, only used as a translation
for physical addresses.

I'm going to be pedantic :-)

Virtual address == translation of process address to physical address
Virtual memory == swapping / paging to secondary storage.

When using the terms, decide what is "virtual" about the noun; in the
case of the address, it's a virtual address 'cuz it's not a real,
physical address. In the case of virtual memory, the memory is virtual,
meaning that it's not really there (and hence is "faked" by paging).

Sorry, just one of my buttons :-)

Cheers,
-RK

--
[If replying via email, you'll need to click on the URL that's emailed to
you
afterwards to forward the email to me -- spam filters and all that]
Robert Krten, PDP minicomputer collector http://www.parse.com/~pdp8/

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