I want to Install Ubuntu Server 21.10 as dual boot system of

[TheFu]

Because this PC is very old, and Windows 10 Home 64-bit, I think Hyper-V Not supported, but ONLY VirtualBox is supported as of running VMs…

This is intel core 2 quad 64-bit, DDR2 8GB RAM, HDD Windows 10 Home 64-bit

BIOS And Not UEFI
MBR and Not GPT

Default boot OS can be configured...? If yes, this depends on OS installed lastly...?

Windows has to be installed first, if you insist on dual boot. I think dual boot is an abomination. Use virtual machines. Your CPU and RAM will easily support multiple VMs. Easily. Linux-based VMs can boot with either UEFI or legacy BIOS emulated. I'd bet that whatever hypervisor Win10 provides (or vbox or VMware $$$ Workstation) can as well. I haven't kept up with Windows hypervisors since about 2011 when I stopped putting Windows on physical systems.

Linux doesn't have artificial limits on using GPT only with UEFI. 32-bit, 64-bit, BIOS/UEFI, MBR/GPT ... doesn't matter. Any combination should work fine. I've BIOS booted an AMD E-350 APU from a GPT 4TB drive long, long, ago with no problems.
MSFT added arbitrary limitations to force new hardware, EFI deployment, secure boot, and a few other things that were issues for Windows, but not Linux. EFI booting is recommended by the Linux Foundation, as is using Secure Boot, for the most secure Linux system. Read more here: https://www.linuxfoundation.org/blog...cybersecurity/ But by dual booting, all the systems on that hardware are just a little less secure because the entire device cannot be encrypted.
I'm bad and don't use UEFI or Secure Boot on my systems, except for 1 laptop. Many of my systems don't have GPT boot devices, but if they have more than 1 storage device connected and that device was added since around 2012, then it has a GPT partition table. This is regardless of size. 32GB or 8TB ... they are GPT. That 4TB HDD from the E-350 has been moved forward to 2 newer systems and 3 replacement HDDs, but I've never changed the partition table to GPT over all these years. The OS has been upgrades, not installed fresh all these times.

Core2 Quad supports VT-x, period. https://ark.intel.com/content/www/us...6-mhz-fsb.html All Intel Core2 CPUs support VT-x. It is more than sufficient to run multiple virtual machines with hardware acceleration. The hostOS can be Windows OR Linux. Generally, people choose the OS where they want the best GPU performance as the hostOS. Then there are people like me who always choose Linux. Always. That completely removes hardware compatibility issues from Windows - so my really old printers and scanners which haven't been supported by Windows since before Vista can still be used.

Think I've posted most of this earlier in this thread. Everything the other posters here are saying is all true too. This is the superstar team trying to help.

[lsepolis123]

Can you reply this: Can practice in a UEFI/GPT hp Z440 Workstation system, but inside VM in Vmware Workstation pro 15.x setup And the VM be as BIOS/MBR OS...? This because after Testing i will try in an old system BIOS/MBR this... process... can I make this testing...?

[lsepolis123]

So, the answer is
YES I, CAN TEST BIOS/MBR FROM UEFI/GPT Host:/VM:BIOS/MBR...
So review, Vmware docs or search Google or Vmware forums...correct?

[MAFoElffen]

Yes. For many VM Hosts, when you create the VM Guest, you can choose with BIOS firmware type you want to simulate.