question about 64bit guests on 32bit hosts

[goodcooper]

i know it can be done with a machine (cpu + bios) capable of VT, but what about memory addressing...

can a 64bit guest address the >4GB that the 32bit host cannot?

 

[Christopher]

No, the virtualization software running on the 32-bit host operating system can only use as much ram as the host OS can give it.

 

[lopoetve]

Not true Since you're passing the cpu through, you can use the full 64bit range.

 

[dbwillis]

?
So if I have a 12gb box with XP 32bit on it, windows seeing 3.25gb when booted up, I can make 2 other Vista64bit guest with 4gb each?

 

[dr.stevil]

I suppose that you could, but that doesn't make a lot of sense to me since the host OS, afaik, is still telling vmware/virtualpc/etc what kind of hardware and such is installed. For instance, I can't connect my iphone to a guest OS unless I have itunes/bonjour installed on the host to pass it through to the guest.

the real question is, why would you run 12gb of memory on a 32bit os?

 

[lopoetve]

I suppose that you could, but that doesn't make a lot of sense to me since the host OS, afaik, is still telling vmware/virtualpc/etc what kind of hardware and such is installed. For instance, I can't connect my iphone to a guest OS unless I have itunes/bonjour installed on the host to pass it through to the guest.

the real question is, why would you run 12gb of memory on a 32bit os?

And VMware is ignoring the host OS and talking directly to the CPU

ESX 3.X is a 32bit operating system, for instance, too

 

[dr.stevil]

And VMware is ignoring the host OS and talking directly to the CPU

So would this be the case on a non-vt enabled chip as well? How does it determine how much memory to save for the host? My experience with virtualization is limited to basic/home stuff

ESX 3.X is a 32bit operating system, for instance, too

I stand corrected lol

 

[lopoetve]

So would this be the case on a non-vt enabled chip as well? How does it determine how much memory to save for the host? My experience with virtualization is limited to basic/home stuff



I stand corrected lol

Non-VT won't be able to run a 64bit guest on a 32 bit system

 

[Christopher]

Not true Since you're passing the cpu through, you can use the full 64bit range.

Yes, a 64-bit guest running inside of a VM on a 32-bit host can use 64-bit addresses for memory access. However, that address space has to map to physical RAM somewhere. In a hosted system such as VMWare workstation or Server, the host OS manages the mapping of the VM process to physical RAM. Thus, the VM process can only physically address a 32-bit address space.

 

[dr.stevil]

Yes, a 64-bit guest running inside of a VM on a 32-bit host can use 64-bit addresses for memory access. However, that address space has to map to physical RAM somewhere. In a hosted system such as VMWare workstation or Server, the host OS manages the mapping of the VM process to physical RAM. Thus, the VM process can only physically address a 32-bit address space.

so if I understand you correctly, as long as the (32bit) host can use tricks to address all of the memory space, then you can run a 64bit VM with no memory limitations, but if you're using something like XP as the host, you'd still be bound to the 4gb limit?

 

[lopoetve]

sec...

edit: Yep- this is one of main advantages of VT- it lets the VM use the CPU's memory adressing range, regardless of the host OS. I just built, installed, and ran a Vista64 guest with 6gb of RAM on my XP32 machine. It saw, identified, and used all the memory without an issue. In VMware workstation.

like I said - VT lets you ignore this limitation - it passes the VM process through the host OS straight to the hardware, letting you ignore those limitations.

 

[lopoetve]

so if I understand you correctly, as long as the (32bit) host can use tricks to address all of the memory space, then you can run a 64bit VM with no memory limitations, but if you're using something like XP as the host, you'd still be bound to the 4gb limit?

If you have VT, there is no limit for your VMs.

 

[dr.stevil]

oh ok, thanks for the clarification it's good info to know

edit: sorry op

 

[Xaero_toast]

Non-VT won't be able to run a 64bit guest on a 32 bit system

Non-VT won't run a 64bit guest on anything.

I tried to run a 64bit guest on a 64-bit host, without VT.

It are not work.