Virtual machines

[ppppenguin]

Anyone with experience of VMs? I'm looking for guidance to avoid silly mistakes and a bit of hand holding as I venture out into the world of VMs.

I've had a first dabble, using VirtualBox. Using W7 64 bit as the host OS I've successfully created XP and W2K VMs. It feels weird the first couple of times you instal an OS on a VM but it seems to work.
https://www.virtualbox.org/

Vbox is free and pretty comprehensive but there are many other VM packages up to the full industrial strength stuff from VMware. Most of VMware's stuff is paid for and aimed at enterprise level computing but they have some free stuff too. Such as a bare metal hypervisor http://www.vmware.com/uk/products/vsphere-hypervisor

This brings up the question of what sort of VM. Bare metal or hosted? Vsphere is a bare metal hypervisor. This means it's installed directly on the hardware with OS's runnng under it. Vbox is a hosted hypervisor which requires a host OS.

What am I trying to achieve with VMs? First and probably most important is when I fiinally move away from XP to W7 or elsewhere I will still need to run software that needs XP. Some software I run would probably be happier under W98 than XP so I could create a VM with W98. Second is security. I can clone a VM for some experiments and discard it at the end without risking anything. Third is portability. I can copy a VM to a memory stick and run it on another PC.

I'm not really a software and PC enthusiast, they're primarily tools for me but I've had to learn a lot more about them than I ever really wanted to.

[Nick]

I can help a bit if you want. One of the teams I run manage a few 100 VMs (and a lot of other stuff) , mostly under Hyper-V  and more recently VMware..

[ppppenguin]

I suppose the first real question is whether to go for the complexities of a bare metal hypervisor. I've looked at the installation notes for Vsphere and there's stuff about setting IP addresses, DNS etc that look pretty irrelevant to the kind of desktop virtualisation I want to do. Also there's licensing to be done, even though it's free.

On this basis, Vbox seems more than adequate. It's released under GPL and getting started is very simple. I've also played with it a little and it seems like it will do the job for me. So is there any reason not to use it? Host OS will be W7 64 bit, guests will be, at least initially, XP and possibly W98.

If I wanted one or more W7 guests under the W7 host I presume that the licence for my host OS won't work for the guests. How do you solve that problem? Apart from illegally.

[Radio Fixer]

I bought W7 Professional as it was supposed to run legacy XP programs on a VM.  When first installed it did work but what I never solved was printing from the application.  This was an old version of Quark, a page layout program, that I had used for many diagrams.  I asked various PC magazines how to solve it but they never came up with an answer.  Eventually I just gave up and used it just for reference on screen.

Now as time has moved on I don't use it at all and I'm not sure it even opens.  I shall probably delete the XP option and recover the disc space on my SSD.

I have a feeling that VMs always have bugs and drawbacks compared to the proper hardware the software is supposed to run on.

Gary

[ppppenguin]

AFAIK the legacy XP facility in W7 pro isn't wonderful. So far, running XP in Vbox has allowed some older software to run OK for me. I don't think I'll be needing this sort of functionality but the fun comes when getting the VM to talk to external ressources. I think that network and printer virtualise pretty well. Sound not quite as well and if you want W98 style direct access to parallel ports then it's probably not going to happen.

[Mark Hennessy]

and if you want W98 style direct access to parallel ports then it's probably not going to happen.

More like "definitely"...

NT-based systems have the HAL (hardware abstraction layer) sitting between the hardware and the software. To my knowledge, virtualisation software cannot bypass the HAL, so has to pass IO via the HAL plus any other abstraction that might be happening as part of the virtualisation. I'd love to be wrong, but as far as I know, that's the case.

Here, we tend to do hosted VM for quick non-critical stuff and hypervisor when it matters. If you host, you have a whole OS that can fail, causing the VM to go wrong. Against that, the ease and flexibility of a hosted solution might be worth that risk. Horses for courses, etc...

[ppppenguin]

In theory I suppose the VM could trap any direct hardware access instructions and pass them through a virtual device driver. Probably not easy. I suspect that Dosbox (a VM for DOS) has to do something like this to get older games to work.

[Nick]

The HAL was so NT could run on differing hardware platforms, i.e. other than Intel. Specifically, this was targeted at the DEC Alpha AXP chip line - I still have an Alpha AXP/433 NT 4 box in my office somewhere - this was NT natively compiled for AXP, not an emulation. At one time DEC had a huge number of s/w engineers on the Microsoft campus at Redmond specifically engaged in doing this parallel port to simultaneously support Intel x86/AMD i586 & AXP architectures. This all ended with NT 4 - later versions did not support AXPs and DEC killed the line - they were bought by Compaq who in turn were bought by HP.

As has been mentioned, hosted VMs rely on an underlying OS e.g. IOS, Linux, Windows etc. to run normally - I/O for the VM has to be shepherded from the hardware through the host OS to the VM - this makes this sort of VM pretty slow and there are many layers that normally fast stuff like disk I/O has to go through.

Real, production, VM systems like Microsoft's Hyper-V and VMware rely on a very thin & fast "hypervisor" that virtualises the underlying hardware for each VM - in the case of Hyper-V, there is a controlling O/S, also confusingly known as a "host O/S", that is also a VM (known as the primary VM) - you can login to the primary VM and control the other VMs via a tool known as the Hyper-V Manager.

Certain chipsets have hardware virtualisation support to make the running of efficient hypervisors possible. AMD call this AMD-V and Intell call their's VT-x - interrupt handling support for VMs is also now on chipsets - AMD call theirs AVIC and Intel's is APICv.