In article <44ec609a$0$16660$ l>,
Michiel <> wrote:
>But i am just wondering...
>Like Windows XP when you insert an additional 256MB on the installed 256MB
>the system is running smoother... is that also what will happen with the
>PIX...?
hehe... Or is it purely depending on the amount of memory free...
>for example if the memory reaches below 1MB the system is slowing down...?
On the PIX, if you have enough memory for everything that is
currently active, then more memory does not speed things up.
On many operating systems (not PIX, but I don't know about XP), once
you have enough memory to handle everything this is running simultaneously,
adding more memory just changes the point at which you could run
even -more- simultaneously. I say "not PIX" because PIX allocates
all the memory it needs for the OS at the same time, and then more
memory mostly just controls the number of connections (and translations)
you can have simultaneously.
It is true that if you are -very- short on memory then with most OS's
(including PIX), operations slow down as the OS has to look harder to
find free memory for whatever it wants to do. Usually, though, a few
hundred Kb is more than enough.
There is a way that XP could potentially run more smoothly with
extra memory. I don't know if XP does this, but I know SGI's IRIX
operating system does. If you have extra memory hanging around, then
the operating system can take it and use it as a disk cache, storing
the most-used files completely in memory, so that the next time they
are requested they do not have to be fetched from disk. I have not
seen any evidence that XP does this, but I am not an XP expert by
any means, so I might have been looking in completely the wrong place.
On the PIX 506E, there is something that extra memory can help with.
If you have the memory, then you can use "turbo ACLs" (compiled ACLs).
That is a mechanism that the PIX can use to figure out in a short
sequence whether or not any particular packet matches an access
control list. When compiled ACLs are not used, the PIX must start
at the beginning of the list and go through each step in sequence
until it finds the step that matches (or gets to the end);
with compiled ACLs, it can do it without having to search the list.
The PIX 506E allows ACLs to be compiled if the ACL contains at least
19 lines (below that it is faster to search the list sequentially.)