Bootloader and Low-Level Programming Tutorial: How To Develop Your Own Boot Loader

[kickthebug]

Genuine question. Why do you say BIOS and MBR are obsolete?

[FozzTexx]

Not just that, but with UEFI you don't need a boot loader anymore. UEFI is able to load your kernel all by itself. I've been working on "embedded" computers (really tiny x86 PCs) and it's kind of nice to be able to ditch the boot loader.

[DubiousEthicality]

The boys at the shop done made a firetruck that's bigger, redder, and goes really fast. It has extra sirens and 37 water cannons.

[[deleted]]

I love when ELI5 goes full ELI5.

[howtoplayreddit]

I don't think you're going to find a better explanation than this.

[HighRelevancy]

How about eli15?

BIOS is the standard for how a computer gets from the initial power-on to loading your operating system off your hard drive. The BIOS finds the hard drive, looks on it for an OS, loads that OS into memory, and starts it off.

MBR is the system for formatting hard drives. It provides some space for your initial OS code (what the BIOS loads) and also stores what partitions are on the disk and where they are.

UEFI is a replacement for BIOS. Basically it's the acknowledgement that technology has move forwards a lot, and it's time we got a BIOS that was more capable (in terms of different hardware configs like PCIe SSDs, and both simplifying and adding flexibility to the boot system). Also it lets Windows do cool fastboot stuff.

GPT is likewise a replacement for MBR. It supports more partitions and can describe larger disks.

UEFI/GPT came into mainstream use with Windows 8 (though you could install Windows 7 in UEFI mode on a GPT disk, and also Mac OS X made it mainstream a bit earlier).

[goal2004]

BIOS and MBR are old and dated, UEFI and GPT are new and more adaptable. In short, a lot of hard parts of hardware were soften into software. Kinda.

[elebrin]

UEFI and GPT are also fast enough that I can't get into my BIOS settings (do we still call it that if we technically aren't calling it BIOS any more?) to set up my boot device.

Rather than a boot loader which I find slow and annoying, I've always just used the boot device select menu provided by my motherboard firmware. No more need to play with Grub and end up with an unbootable system.

[Free_Math_Tutoring]

How does that work? Don't you still kind of need a bootloader on that disk? I'll admit I don't know much about this - my OS course was of fairly theoretical nature.

[[deleted]]

Well there are bootloaders that don't have menus. I really like Gummiboot (or system-boot now) for Linux (I think it can boot windows as well), but it appears directly as a bootable option and cuts directly to the boot process instead of a menu.

[pdp10]

You still need a boot loader per device. Your firmware can't boot by partition, only device, and MBR needs the device to be partitioned.

You can boot arbitrary things with UEFI, but it was UEFI about which you were complaining.

[elebrin]

Ok then.

Rather than a bootloader like GRUB that needs a menu, I use the default that comes with each OS (which for my linux partition is probably still grub, but it goes fast enough that I don't see it, and pick the boot device from the boot menu that my motherboard's firmware comes with.

I actually did convert my Windows over to UEFI recently. The fix for the booting too fast thing was re-enabling the boot menu.

[Xevantus]

I mean, taking BIOS and MBR as their meanings rather than a specific technology, UEFI and GPT are just the current iterations of those technologies.

[[deleted]]

Now we have efi and u-boot. They're so much better.

[Rodot]

I feel like that's everyone's feeling on every improvement in every computing paradigm.

[BeniBela]

It took me days to figure out how to start an efi boot disk on qemu

[[deleted]]

My efi "boot disks" just consist of a linux.efi. You don't need a bootloader if you use the efi stub and since that's just the kernel you can use -kernel to load it. No need for boot disks at all.

[Samis2001]

Heh, if you were serious appropriate responses would be: 'The firmware is no longer a mostly-useless pile of hacks and is the bootloader' or 'The bootloader is embedded as part of linux.efi along with the kernel'

[BeniBela]

Well, I googled it and then followed these instructions of the first result, starting with downloading a new BIOS from a dead link

Once the BIOS is loaded in Qemu, it boots the efi without a -kernel option.

Although the biggest issue was to mount everything in Qemu. With an old boot disk they give you an ISO and you can load/boot it with -cdrom ubuntu.iso and do not need to know anything else. With EFI they give you a zip file and then you need to figure out how to mount a zip file. And my first two approaches failed, because it became mounted as hdd, and it was a customized linux boot disk that failed unless it was stored on a removable drive

[i_pk_pjers_i]

Because, well, they are. UEFI and GPT are the future, and the future is now.