As far as I know, MSinfo will report the TOTAL amount of ram from the BIOS.
System Properties will report the amount of RAM available after Video, BIOS
and device Caching takes effect. You can confirm this by changing these
values in the BIOS. Do this as a temp measure cause it will affect
performance. But you will see these numbers change (albiet slightly). Also
remember, that everytime an app is switched or minimized, the OS has to
virtual the Adapter Memory to accomodate a repaint (for want of a better
word) of the video data to be presente on the monitor.
Task Manager reports the amount of memory available for all processes and
services that are loaded (sounds bizaare, but read on). If you add these
values up reported by TM, and then subtract the amount, you should come
close to the amount that SYS prop is reporting. For example 4.0 - 3.25 = the
amount of ram used by services etc reported by TM (or quite close).
We should keep in mind that the WOW64 (and WOW32 as well as WOW16 - also
called WOWEXEC) bit subsystem (these are the ones that allows us to run CMD
and the like) require spurious amounts of ram to support network, cd rom and
related file systems from a DOS (YUP it's still around, we jsut call it:
cmd/command) prompt. That's how we can still access these resources even if
it is a 16 bit app (I know, not a lot of these around - but there are an
awful lot of POS systems that do this - Pickel Point etc.).
If you look at autoexec.nt and config.nt in %winroot$\system32 you can see
what values are "Standard/Normal" in there to support CMD and/or Command.
You can tweak them (not really recommended). When NT (i.e. NT4/NT5) fire up,
the OS loads these files, parses them and configures ram to accomodate them.
Each time you run an installation app (MSI or CMD etc) the ram specified
(and related settings) are allocated to the OS cache. In some cases (for
example SQL installs) yoy may see a little DOS type window pop up. This is
part of the WOW layer and uses additional ram as identified by the above .NT
files and the OS parsing of same.
Sorry, WOW stands for Window On Window - comes from the NT 3.5x days and is
still around.
The OS "SERVICES" and "SVCHOST" preocesses also continullay grab and discard
memory based on the state of the system at any given moment. In addition,
the OS will periodically ananlize application performance (in terms of APP
and DATA ram requirements) and adjust itself accordingly.
Another consideration; every network connection (either LAN/WAN or WEB) uses
small amounts of ram to retain and manage PSP (Program Segment Prefexes) and
Cache to assist the OS in manageing these FILE systems. Each Pipe (Named
Pipes etc) require REAL RAM to function properly and efficiently.
Then of course there are the DLL (Dynamic Link Librabries and DCOM)
critters. Look at Internet Explorer -> Tools -> Programs -> Manage Add-ons.
You will see some DLL (or activex) controls loaded. Search for these on your
system, the use something like Dependancy Walker to see how much ram these
bad boys take. These critters ARE NOT reported in TM!!! Yet, these jammers
are fired up with the OS!
There are essentially two types of memory available to NT:
1) RAM: I call this "REAL ACCESS MEMORY" - that's what the Prop Page
reveals,
2) RAM - Random Access Memoroy OR Virtual RAM: This is PRETEND memory!. Even
though you may have 4GB or RAM (see #1), the OS will still create Virtual
Instances of the machine to allow 4GB of RAM (flat address space) to
applications. These apps run in an NTVDM (NT Virtual Machine). They don't
really have 4gb RAM (even though it's there) because the OS has to SWAP the
entire context of an app (including things like CPU state and Registers)
in/out of RAM to the swap file or another area of ram.
And last but not least, if you go to System, Properties, Performance, then
Advanced and TWEAK the setting there, the values above will change. Again,
it's part of the OS's way of trying to optimize memory uses.
I realize this may seem rather strange and obtuse, but if you read some
articles on UNIX based memory management (which is basically where NT gets
it from), it may be clearer.
Here are some links that detail this far more expertly and specifically than
this:
http://www.ittvis.com/services/techtip.asp?ttid=3346
http://www.brianmadden.com/content/content.asp?id=69
A Thread as well:
http://www.tsgserver.com/pipermail/list_tsgserver.com/2005-April/006141.html
Sorry for the rambling, just trying to fill in the blanks.
