use more than 3gb with pae on xp 32bit?

[jmar83_the2nd]

hi at all

i use virtualbox with 32 bit xp host & guest.

i have 4 gb ram, 300mb will be used for the graphics; but i use win xp 32bit, so i only can use 3 gb.

my question: can i use "pae" (physical address extension) to use more memory of these 3 gb for my win xp 32bit guest?

"pae" is activated on both systems (in boot.ini in the host and in the virtualbox settings for the guest...)

thanks for feedbacks!


regards, jan

[mpack]

No, your guest is allocated memory by the host and hence the guest cannot receive more memory than the host knows how to allocate, and in fact on a 4GB Windows host that will be substantially less than 3GB available to the guest, because you must leave enough for the host. Probably the guest can have no more than 1.5GB RAM.

Also, it is pointless allocating too much graphics RAM to a guest, since the guest doesn't have a GPU. All of the actual graphics work is carried out on the host. The guest should have enough simulated VRAM to cache a few full screen images, and that's all. Go with whatever the VM settings dialog recommends.

[jmar83_the2nd]

thanks for your anwser.

what i if i use a 32bit xp guest in a 64bit winxp or win7 host? can a 32but guest use more memory on a 64bit host? (max 3 gb, i know)


regards, jan

[Rootman]

Yes, in the case of a 32 bit guest on a 64 bit host it CAN allocate more than 3GB ram - PROVIDED that the HOST has more than 4 GB, preferably like 8 or more. If I remember right it seems that with the BIS that VBox provides the guest can see about 3.2 GB. You can allocate 4 and look at the PCs properties and see how much RAM it is actually seeing and then shut the guest down and set it at that much.

Another issue is does the guest really NEED that much RAM? Unless you are doing something that requires a LOT of RAM on the guest allocating a lot of it is just wasteful and prevents the HOST from using it.

[mpack]

A typical XP 32bit guest runs very sweetly with 512MB. It was designed to require far less.

[Rootman]

Yep, UNTIL you add an antivirus program, and a modern browser with a bunch of addons, an Office suite, and etc. Apps have gotten out of hand and there may very well be a NEED for more RAM than 512mb, my advise is only allocate as much as you MUST have for adequate performance.

[mpack]

My own XP VMs all happily run the latest Firefox in 512MB, I don't use resident antivirus on either guest or host so I can't tell you what that requires. No matter, if the host can afford 1GB then there's no reason not to go with that.

[jmar83_the2nd]

now i use win xp x64 as host, and win xp 32bit as guest - my host system has 4gb of ram, so now i use 2.0 gb for my guest. (on the guest, i use some servers - apache, mysql etc.)


the guest now seems to be faster, this is VERY STRANGE. i thought it must be slower, because of 32bit emulation on the host system? i cannot explain that - somebody can?

thx for feedbacks!

[mpack]

2GB is IMHO too much for a VM on a 4GB host, and simply not necessary for an XP 32bit guest. Go with 1GB as already suggested.

The reason 32bit emulation doesn't seem slower is because there is no 32bit emulation. Code runs natively on the host CPU, as always. A 64bit CPU is able to run 32bit code (obviously: otherwise you wouldn't have a choice of 32bit or 64bit OSs on the same host PC).

[michaln]

guest now seems to be faster, this is VERY STRANGE. i thought it must be slower, because of 32bit emulation on the host system? i cannot explain that - somebody can?

There simply is no penalty for running 32-bit code on a 64-bit host OS. There is no "emulation", an AMD64/Intel 64 CPU can run 32-bit code just as well as it can run 64-bit code.

[jmar83_the2nd]

sure, i know that the 64 bit x64 cpu's are able to execute 32bit applications / operating systems ("x86")

but if i use a 64bit windows with 32bit applications, the cpu is not 100% in 64bit mode? that means in a 64bit windows, 32bit applications will be executed DIRECTLY in a 32bit mode on the cpu?