I recently got away from partitioning for Linux operating systems ans
installed virtualbox with with win 7 as host. What an extremely innovative
process. I would really appreciate some super literate user to explain me a little of how it works.
The short answer Virtual Box creates a software interface to emulate hadware (including monitor, network card, ram, hard drive, etc).

And I figured out events on VirtualBox can effect your host. This ranges from soft ware events (shared folders) to hard ware events.

But to what degree does it effect host?

1. Lets say you are installing Debian which I have and I gave 20GB to VB and
accepted all minimums like ram etc.
2. Then I loaded Ubuntu using same 20 GB
My basic question is if I continue in this fashion like an extended partition
with multiple Linux Partitions when I exceed that 20GB doe it not need unallocated GB on HD or can it or will it capture some of that 300 GB I have of NTFS.
Probably explained this wrong, but hope someone understands and thanks

If you create a 20GB disk for a VM, the disk size will not automatically grow. This is not to be confused with the feature that allows you to create a 20GB disk and have it only use as much physical space on the host drive as necessary, up to 20GB. If you want to increase the size of a drive that you originally created at 20GB, you can use the VBoxManage modifyhd command to resize the disk.

Would you be so kind as to elaborate on underlined. And I do not mind starting over as I have no earthly use for that 300GB NTFS. I seldom use windows.
Guess what I am curious about is to be able to use VB same as I used Linux partitioning i.e. give each OS the GB before the fact. Gad I hope I am making
sense. My 80 year old mind may be showing. Thanks really appreciate reply

Short answer from a 66 year old mind: yes.

Sorry (only 34), but that is plain wrong. A virtual harddisk will not automatically grow if it is used to its full extent, you will simply get out of space messages.

@80yearold: Keep in mind that you don't have to use dual-boot in a VM if you want more then one distribution. I prefer to set up a new VM for every distribution I want to try. This way I can simply suspend a VM at any given time and use a different distribution in a different VM without the need to reboot the first WM. It is also easier this way to compare something in different distributions (just run two VMs simultaneous ) and it is possible to set up a virtual network for trying different servers or similar.

VBox is on the host's (Windows 7) 300 GB NTFS partition, the question I was answering was: will the guest OS's use bits of that or unallocated space?

My on this:

There is a way you can allocate more virtual disk space than you have physical hard disk space in VirtualBox: just use a dynamically expanding image. This creates an image that is actually only physically a few tens of kilobytes when first created (may be a bit more; I don't remember exactly ), but it grows in size as the VM writes to it. The only disadvantages to this scheme (that I can see) are possibly slightly reduced disk I/O performance, and you'll have to be careful how much virtual disk space you use in your VMs (since you don't want the VM disk images to expand to completely fill your physical hard disk ).

EDIT: This doesn't mean you can have a virtual disk image of infinite size, BTW; it just means you can allocate a virtual disk image that's bigger than your physical hard disk, or have multiple VDIs that (virtually) add up to an amount larger than your physical storage space.

But that was not the question the OP asked. He asked what happens if the 20GB virtual disk gets full by installing more distros on it. At least as I understand it. If I got that wrong I apologize.
May be the OP can clarify.

I took it to mean would it use another chunk of the host's NTFS partition, or somehow use unallocated space. But, after rereading the original post, he was asking about installing two or more distros on the same virtual HD. I've never tried that.

You are correct that is what I stated, rather poorly probably

I have never attempted a dual boot on a VM and see no reason to. Just create additional VMs.

I've installed multiboot in a VM precisely to test out what happens with GRUB in different versions and how you can recover from errors (especially corrupted partition table errors).

But for testing and learning distributions, yes, separate VMs is the way to go.

Some thoughts - this is not very complete:

Disk space

Normally a VM tool like VirtualBox will create dynamically sized virtual disks, so you could create lots of VMs with disks that are theoretically 20GB but only take about 5GB on the host (after initial installation of the "guest" operating system, for example). As you add data within each guest, the virtual disk will take up more space on the host - up to 20GB but never more. But all the time, the guest OS will see that it has a fixed-size 20GB disk.

So if you make 5 VMs and they are each about 5GB full to start with they would take about 25GB of your host 300GB partition. Over time, they may grow and use up to 100GB (5 × 20) of your host partition. So it might seem as though they are eating up host space, but this is within a strict limit

Access to files and folders

Yes, with shared folders the guest system can access some of your host (Windows 7 in your case) files and folders. If you allow write access anything that happens in the guest could affect any of those files on the host.

Performance and memory

Each guest will use CPU cycles almost as if they were running natively. If you run several guests at once, your computer will be busy, just as when you run several active programs. But when guests are powered on but not doing anything, all the CPU is available to the host or other guests.

Memory (RAM) is a bit different. If you have 2GB of RAM in your hardware, you have to allocate a lower amount to each guest. And if you run 4 guests with say 1GB of RAM each at the same time, your host will run out of RAM and will start having to use "swap" or paging space quite actively, and on most computers this slows down everything quite badly, because it requires disk access.

But having lots of guests that aren't powered on doesn't matter at all - these ones will only use disk space and not have any effect on performance. If you only run one guest at a time it will usually be fine.


Does this help?