Does XP see past 2GB without 3GB switch enabled?

Ok, one of my machines has XP on it with 2GB of ram. I want to upgrade to 4GB. Will my computer see past 2GB or not without the 3GB switch being enabled. I am getting a lot of conflicting information about this. Some say it will not see past 2GB others say it will only see 3.2, or 3.5. Can anyone give me a for sure answer on this?
Thanks.

 

it will see nearly all the 4gb (it'll see all, but can't access all). but apps won't. apps will see 2gb.

i think.

 

32-bit OSes can only recognize 4GB but some of that will be reserved, hence the OS will only "see" between 3-3.5GB.

 

What service pack and what HW such as North Bridge?

The 3GB switch is just for applications that can behave nicely when using addresses above 2GB. Without it single applications will be limited to 2GB of linear address but you could possibly have for instance 3 applications using 1GB of memory each to use 3GB of memory between them or in extremely rare cases a single app can use more through AWE.

 

XP is capable of seeing nearly 4 GB after it subtracts whatever your hardware reserves (I'm seeing 3.48 GB of the 4 GB installed on a Latitude E6500). The question is does your motherboard have any limits that will prevent more than 2 GB from showing up, which is why there is conflicting information: it depends on your hardware. You have to check on your specific model to know if it will take more than 2 GB.

 

Thank you folks for the knowledgeable information. I guess the question is then will I really see a benefit from having another 1GB ram in my laptop give or take.
I run an audio setup off my laptop with VST's and samples so there are times when it gets ram hungry depending on what's loaded.
Money may be better spent in putting it towards a new laptop that will come with Windows 7 where the RAM will definitely not go to waste.
What do you guys think?

 

yeah, new laptop will be worth it for audio thanks to the newer cpu, and more ram, and the better memory managing os. so i'd say go for it.

 

When I put 4 GB in my Vostro 1500 when it had XP it showed up as 3.5 GB of RAM. Odd though cause Vista x86 will see 4 GB of RAM but of course cannot address the full amount.

 

this is just how the os interprets it. xp reports what it can see and use. vista reports what it can see (so the customer is not irritated " i bought 4gb ram and it lists 3.5gb!!"), and reports in the taskmanager, what it can use.

 

the OS(and with proper BIOS) can see 4GB though in the last 1GB, there are lots of reserved range so it ends up as 3-3.5G, this applies to XP/Vista/Windows 7. It is only that they report different numbers, I think 4G is reported in Windows 7 and Vista SP1(?) whereas it was 3.x in XP and Vista RTM. The usable address doesn't change though.

The /3G switch is strictly for the OS telling it how to slice the 4G space, default is 2/2, with the switch it becomes 1/3. Note any application can utilize 3G as all 32-bit application can address up to 4G.

For system that supports PAE(i.e. 36 bit addressing) and you have more than 4G physical RAM, special written application can make use of them, the most notable example is SQL server which can use the above 4G space as its own buffer. Though I faintly remember XP doesn't support the PAE related API, only 2003(and may be 2008) server does.

 

but not all apps are stable >2g because of signedness issues when they compute memory adresses. which is why the 2gb limit was implemented by default. there where tons of apps known to crash rather randomly (it's an impossibly annoying to find and fix bug).

it's much better to define the app limit to be memorylimit/2, so they can make the sign errors and are never affected.

and that's why the 2g/3g switch was implemented. 3g was only enabled on server os', where applications are made for big memory usage anyways. the switch on xp is just there for developers to test their server apps.

at least, that was the intention.

 

That unfortunately I cannot tell as we are venture into buggy program arena

You do have a point that many lousy programmers make too much assumption about word length and pointer size conversion. These problems are supposed to be catched by any decent C/C++compiler(though many would ignore the warning).

 

just remember xp was in 2001. yeah, modern compilers catch it. but we're still using 15 year old apps at work. so imagine in 2001, having the need to run THEN old apps.

there was a good reason for the 2gb barrier per app.

 

And there still is. Basically, for any application that is 32 bit and envision that it needs 2G+ space, it would have its own tricks to do it (PAE, its own VM backed by disk etc.) as they have to cater for the 2/2 situation anyway. For those that don't need that, they still would not need that.

So the 3G switch is only helpful in limited situations, the OS can use those memory for cache anyway in the case of 2/2.

Except of course for those that is written in higher level language like Java/.NET/Python etc. that the programmer no longer do these low level memory pointer thing.


Though your point made me wonder, under a 64 bit OS, a 32 bit application now see the full 4GB addressable space as the OS is out of the picture. Does it mean these random error would popup ?

 

for those old apps, yeah, could be that they pop up, then.

but we're about 10 years after xp day one, so i think the amount of such apps is greatly reduced by now. question is, does setting the compatibility mode to xp an app back to the 2gb limit? that would be interesting.

 

What decides if a 32-bit program gets <2GB or up to 4GB on a 64-bit OS is usually the large address aware flag. AFAIK compatibility mode has nothing to do with it.

 

ok. nice to know.