Windows 7: XP x64 in VirtualBox on Win7 x64 optimum setup

VMs don't work the way some folks think. You're not "dedicating" cores to a VM; you're simply saying that the VM instructions will be allowed a thread path to the host machine cores. The host processor doesn't care what instructions it's executing or where they're coming from since they're all coming through the same pipes. It's no different than running a bunch of programs at once on the host alone. If you have the power like most 8-core (thread) processors do today, I doubt you'd see any difference in drag. You'd be surprised at just how little the cores are used for most apps.

I ran all eight cores when I had the Windows 8 preview loaded on Oracle VM. I even gave it a 100% cap and had no problems switching back and forth to the host. And I'm just running a "old" i7-2600. What really bogs a system down is I/O. Plant the VM disk on a SSD and it will rip!

I sure thought that I was doing when I set this on the host:



And the XP VM only had one CPU simulated within it.

Keep in mind that this was many months ago when I was using an XP host with two physical cores. The CPU scheduler in XP doles out time slices in a round robin fashion... which means if the VM is maxed out, then each CPU is running at about 50%. The host was noticeably slower if I did not "dedicate" one physical core to the multiple VMs. Sure the host still could make requests of that same physical core. I did not work thru each process and force them to use the second physical core. Had I done that, then one physical core would have been dedicated to the VMs.

I realize that the OP is talking about a Windows 7 host with an AMD CPU with 8 physical cores and that the Windows 7 CPU scheduler is different than XP's... but, even within Windows 7, you can "dedicate" a CPU to a VM. It might not be wise, but it can be done and might be best for some setups.

Nope, sorry. Cores are NOT dedicated in VM. If that were the case, my Windows 7 would have stopped completely while I was running Windows 8 in VM since I assigned all eight cores at 100%. It didn't happen. Windows 7 was happily retrieving email, playing music through WMC and running IE-8 with info pages while I was browsing with IE-9 and experimenting with different settings on Windows 8 VM. And there were some file copies from Flash Drives in there too. I was running Eight in windows mode and flipping back and forth to read instructions about Windows 8 on Seven (host). I even had parts of Seven on my second display so I could watch processor activity and keep an eye on temps while watching for email. I should have saved the HWiNFO logs from that test to show you proof. As I recall, all four cores (eight threads) hit turbo at various times but never at same time (they don't anyway) and processor utilization never got above around 80%.

You can't compare a 2-core XP machine to an 8-core Windows 7 machine. It will get smoked every time.

Then what would you say the affinity setting does on the host os?

Affinity "restricts" what cores a program can use on the host. Normally, the settings for all programs will indicate all cores are usable. If you reduce the cores or allow just one core, the program will run slower because all it's instructions have to be run by that core. If the core is busy, the program waits. Affinity does not dedicate a core to the program. The core can still be used by other programs and it will be used. The program that has a core affinity has to wait in line for the core.

The settings in VM are the same in that reducing the cores reduces the amount of work you're allowing the processor to do with the VM instructions. Lower cores means lower work paths and slower work. And if you lower the "Cap", you're further restricting the amount of work passed to the processor. There's no benefit in restricting execution to fewer cores. If there were, we'd all still have 286 processors.

If a core is available, use it!

As I mentioned, "I did not work thru each process and force them to use the second physical core. Had I done that, then one physical core would have been dedicated to the VMs." I was not attempting to dedicate as much as I was attempting to restrict. The only explanation that I have as to why the VMs performed their task just as well when restricted to one CPU as they did when given access to all CPUs is the task was highly repetitive - perhaps sticking with CPU1's cache made a difference.

Since the thread is about Windows 7 hosts - I changed a VirtualBox W7pro64bit VM to use 4 CPUs and ran wPrime. Now the host is noticeably slower with all 4 of its CPUs maxed out. The host's mouse movements are jerky and the host's screen repaints crawl. I don't have a 64bit XP VM on this box or I would test that.

Thanks for your time on this. I don't want to hijack the thread. I'll leave it to those more knowledgeable than me to advise the OP on this setup.

Just because you assign it does not mean it will be used. When I first got this computer, I downloaded and ran a load test that put all 8 cores at 100% load. After watching it for a few minutes, I decided to see what would happen if I opened a browser window, and my surfing was just fine. I even did a youtube vid and that was smooth.

Like I said, After XP gives me the taskbar, core loads drop to almost zero if both OSs are running nothing else on the desktop

I'd run it just like Indianatone said. 4Cores, 8GB of RAM. Both 7 and XP should be fast and stable.

That is understood. Right now, I'm debating about 4, 2, or 1 core, but this conversation has become [to me] more about the efficiencies of running it, and I'm trying to learn, so I keep asking and hoping to find somebody else that has looked into it.

I would expect so.