32-bit guest on pure 64-bit host

[Segfault]

Can I run 32-bit guest on a host which has no 32-bit support?

[BillG]

Yes. no problem.

[mpack]

Moved to "Linux Hosts".

[Segfault]

Yes. no problem.

Thanks! Will clean out the 32-bit stuff from my box now.

[mpack]

Just curious, but why? Is the ability to run code faster in the same space now seen as a negative? Also, afaik even in the Linux world the vast majority of projects are 32bit, since most don't need the additional memory of a 64bit app.

[socratis]

Can I run 32-bit guest on a host which has no 32-bit support?

The host support has absolutely nothing with what's running inside a guest VM. The only thing you care about is VirtualBox. Otherwise you'd never be able to run DOS in a VM.

[Segfault]

Just curious, but why? Is the ability to run code faster in the same space now seen as a negative? Also, afaik even in the Linux world the vast majority of projects are 32bit, since most don't need the additional memory of a 64bit app.

You are misinformed. There are no OSS projects 32-bit only. Only some proprietary software is 32-bit. I think Skype and Acroread maybe. Linux went 64-bit in 2003 (if I recall correctly) and the progress was rapid.
Memory above 1 GB cannot be handled properly in 32-bit mode. Why should I keep 32-bit support in my box if none of my applications needs it?
Read here (it is Linux man speaking, but the limitation is not OS specific): (cannot post links)

[mpack]

Memory above 1 GB cannot be handled properly in 32-bit mode.

In that sentence I object to the terms "1 GB", "cannot", "properly" and "mode".

"1 GB": a 32bit application using a flat memory model can handle up to 4GB, not 1GB. In any case most applications use memory in the x*100MB range, so even if 1GB was the limit it would be way more than enough for all but a tiny minority of apps (*).

"mode": 32bit is not really a "mode", it is a compile option for the app. Of course running a 32bit app does require the host OS to present a 32bit API. Considering all the other crap built into the kernel is this such a big deal? Presumably this API can be loaded on demand, so the cost is just a small amount of disk space.

"cannot"/"proper": On Linux hosts even a 32bit app can use >4GB, i.e. it is not actually restricted to a flat memory model. Whether you consider that "proper" or not is something of a value judgement. If the host OS (as opposed to the app) is 64bit then the app's flat 4GB allocation can occur anywhere the host OS's physical address space, so I've no idea what that "cannot use memory above 1GB" assertion means.

On the other hand a 32bit app doesn't need to preserve the upper half of 32bit registers when you do a context switch, and it only needs to push and pop half as much data for a function call (for those args not exclusively passed in registers), i.e. 32bit apps will go faster.

(*) 1GB is a huge amount of memory. Consider a spreadsheet app which allocates a generous 32bytes on average to each cell. 1GB of RAM would be enough for a spreadsheet with 33.5 million non-empty cells.

[Segfault]

Done. Directories /lib32 and /usr/lib32 are gone, I even recompiled the kernel without IA32 emulation. VirtualBox works as nothing happened. Thanks again.

Re: memory usage. My OS takes 47 MB of RAM, with GUI loaded with all bells and whistles 107 MB is used. Probably it would be a little less if I was using 32-bit OS, but should I care? In return I have direct access to all of my 8 GB.