Mike Miller wrote: > On Fri, 26 Dec 2008, Elvedin Trnjanin wrote: > > >>> They also offer the "Intel Core 2 Duo T7250 (2.0GHz/800Mhz FSB/2MB >>> cache)" for $100 more than the T5800, but what is the difference >>> between the T5800 and the T7250? Well, that information is not easy to >>> find for some reason, but it seems that the T7250 supports Intel's >>> Virtualization Technology while the T5800 does not. >>> >>> I want to run Virtual Box with Win XP Pro in it. So how much will the >>> Virtualization Technology help me? I'm guessing that it will help >>> enough to be worth $100. Any opinions? >>> >> The "Virtualization Technology" will not help you at all. VirtualBox by >> default disables them as they are not as efficient as whatever they're >> using - check the FAQ for more information. >> > > Do you mean the VirtualBox FAQ? It is here... > > http://www.virtualbox.org/wiki/User_FAQ > > ...but it does not mention "Virtualization Technology" or "VT". > > > Sorry, it was the User Manual. I recall before Sun took over that it was on the FAQ. Here is the snippet - "By default, VirtualBox uses a technique called “software virtualization” to run a virtual machine on your guest computer. In a nutshell, this means that the code in the virtual machine (the guest operating system and other programs installed in the virtual machine) is allowed to run directly on the processor of the host, while VirtualBox employs an array of complex techniques to intercept operations that may interfere with your host. In those cases, VirtualBox needs to step in and fake a certain “virtual” environment for the guest. For example, if the guest attempts to access its hard disk, VirtualBox redirects these requests to whatever you have configured to be the virtual machine’s virtual hard disk – normally, an image file on your host. VirtualBox has very sophisticated techniques to achieve this without any special hardware. However, modern Intel and AMD processors have support for so-called “hardware virtualization”. • The virtualization technology built into AMD’s 64-bit processors is called “AMDV” (originally referred to with the “Pacifica” codename). In addition, starting with the Barcelona (K10) architecture, AMD’s processors have been supporting nested page tables, which can accelerate hardware virtualization significantly. VirtualBox added support for AMD’s nested paging with version 2.0. • Intel has named its hardware virtualization VT-x (it was originally called “Vanderpool”). Intel will ship support for nested page tables, then called “Extended Page Tables” (EPT), with their new Nehalem processors. These CPUs also introduce tagged Translation Lookaside Buffers (TLBs), which Intel calls “Virtual Processor Identifiers” (VPID) and which reduce the need for expensive TLB flushes. Both EPT and VPID are supported by VirtualBox starting with version 2.1. While VirtualBox does support the hardware features listed above, they are optional: you can enable or disable hardware virtualization individiually for each virtual machine. In fact, depending on the workload, VirtualBox’s software virtualization may even be faster than hardware virtualization. Other virtualization products that require hardware virtualization are usually much less sophisticated and tuned compared to VirtualBox. With VT-x and AMD-V, a special CPU environment has to be entered in order to execute guest code and whenever activity of the VMM is required, this environment has to be left and then entered again. This can be an expensive operation and in many circumstances, the benefits of hardware virtualization may not outweigh the performance penalty. On the other hand side, with hardware virtualization enabled, much less virtualization code from VirtualBox needs to be executed, which can result in a more reliable system. So if you run into problems, you may want to try enabling hardware virtualization." >> The only way that it would be $100 dollars better is if the other >> processor isn't a Core 2 architecture or it is, but isn't nearly the >> same clock speed. >> > > What other processor? Are you suggesting that it is possible for one > computer to run two CPUs with different clock speeds? > I'm suggesting that the $100 price difference means there is a lower end processor that was part of the base version, such as AMD or lower spec Intel processor. > Here is what someone on another list had to say: > > "Intel VT will help quite a bit - it's worth the extra $100. VT (and > AMD's AMD-V/SVM) are essentially hardware-assisted traps for non- > virtualization safe instructions. Virtualbox/VMware/whatever should be > able to treat the virtualized CPU as just a piece of actual hardware, > leaving the emulation of non-virt-safe instructions to the *actual* > hardware. > > "If you ever go the Xen route, and want to run a Windows VM, you'll need > VT or AMD-V. It's well worth the extra dough even if you don't ever touch > Xen or other low-level VM monitors." > > > I suppose saying "will not help you at all" earlier is too extreme; they help, but not an extra $100 sort of help. > Obviously I will be needing more opinions. > > Mike > >