How many OS?

[nForce]

How many Operating systems can I have on the hdd for multiboot?

Legacy BIOS and UEFI. I don't know why is it called "Legacy".

[Halcyon]

I don't think there is a hard limit, I think it depends on the type of OS and boot loader you're using.

Also, BIOS is "legacy" because it's old technology but is still present in most systems today. UEFI is a modern replacement but not all operating systems support it.

[nctnico]

The limit is probably the number of primary partitions (which is 4 IIRC). But... using a virtual machine is a much better option.

[SeanB]

Generally you will have GRUB as a bootloader, and then you select the parttions you want to boot, and if using Linux you can have multiple kernel versions as well. However typically you have Windows whatever, perhaps another Windows version, Linux in however many flavours you want ( typically Debian, Suse, Redhat or Slackware as the major brands), then you can have all the BSD versions you want ( or Hackintosh if you select the hardware right), but you do need to allocate a chunk of hard drive to each, and while the 'nix's are pretty happy running off almost any partition, your redmond products tend to want to be the primary partition.

Otherwise the route is to install a Hypervisor and visualise all the OS versions you want, and thus you can have multiple ones running at the same time, hardware capability dependant.

Or install basic Debian, install Virtualbox and the extensions, and run however many OS versions you want as a virtual machine on it in fullscreen mode. That is how I tend to run Windows, as making a VM copy is quick to test out things I am not sure of, plus you always then have a snapshot to start over again from in case things go wrong. You get USB passthrough that mostly works as well, for a wide range of hardware as well. Last time I actually booted the Win7 real partition on the laptop was when it was new, to make the recovery DVD's, and then once again afterwards to run Gotowebinar for Starship Sofa's Jerry Pournelle, Larry Niven and Greg Bear live interview. Otherwise it is just extra storage in the leftover space after resize.

[Ampera]

With GPT boot, you can have a theoretically infinite number of partitions, but some implementations do restrict this (128 on Windows)

[nForce]

With GPT boot, you can have a theoretically infinite number of partitions, but some implementations do restrict this (128 on Windows)

GPT uses UEFI, and MBR uses BIOS?

[tszaboo]

Why would you have more than 1? Just have a host and Virtualbox everything else you need.

[Mr. Scram]

Why would you have more than 1? Just have a host and Virtualbox everything else you need.

Going native does have its benefits, though dual booting comes with its own potential problems.

[Ampera]

With GPT boot, you can have a theoretically infinite number of partitions, but some implementations do restrict this (128 on Windows)

GPT uses UEFI, and MBR uses BIOS?

GPT and MBR are partition tables. They get placed on drives in order to organize data within those drives.

BIOS and UEFI are standards for PC compatible firmware. BIOS boots by loading Sector 0, provided it contains a magic number, into memory and executing it (the bootstrap can then load further code)
UEFI boots by detecting an EFI system partition (formatted FAT32) that contains bootloader data to load various operating systems on disc. It finds the right binary to execute based off special strings written to the firmware.

MBR is limited to 4 primary partitions, but you can use MBR, BSD, GPT, and a few other partition tables (I think) to boot using BIOS and UEFI, and you can also have multiple disks, mounted to allow booting to systems on there.

If the question is, how many operating systems can I stuff onto one machine? The answer is you'd probably never reach it, because even though there are limits, they usually can by bypassed in one way or another. You'd likely run out of meaningful drive space and even HBA connectors before you'd ever hit any hard limit.

[nForce]

Thanks Ampera, but I never noticed when installing OS to have an option to choose partition table.

[Ampera]

Thanks Ampera, but I never noticed when installing OS to have an option to choose partition table.

With Windows, I believe it defaults to GPT on UEFI systems since either 7 or 8, and MBR on BIOS systems any time else.

On most Linux distributions where you manually partition a drive, you have the option between GPT, MBR, and I also think sometimes BSD partition tables, same thing with FreeBSD and derivatives.

In practice, there isn't much of a difference. If you only have a few partitions, MBR works as well as GPT on drives 2TB and under, possibly even a bit better. To my knowledge, traditional BIOS booting (IBM compatible) can boot off of literally anything, so long as it has the right magic number and the code is in the right place. You don't even need a partition table, nor a file system, like many old PC booter software didn't, but for modern uses, it's all file systems on partition tables.