In 1999, David Zimmerli wrote an article in EDM/2 in which he inaugurated the project aiming to replace OS2LDR, OS/2 operation system loader. He wrote a stub program which was loaded by the boot partition MicroFSD and tested the use of its routines. The project was not finished until osFree project in 2003 has taken its sourcecode as a starting point of osFree kernel loader implementation. We left the name of the project as is because it resembled the name of osFree project, is free and opensource, and used Zimmerli's program as a base. It was rewritten, so none of original code remained in it, but we decided leave the name as is. It's primary goal is to load L4 microkernel, but we decided to make it as general purpose as GRUB, and to fix some GRUB's misfeatures and continue its general concepts, like multiboot compliance and OS-neutrality history. We make our loader more modular and extensible. And, we developing support for kernels, other than multiboot ones. Loading of Linux-like kernels and support for chainloading unsupported kernels were moved to separate loader modules too. They were implemented as a separate multiboot kernels. The multiboot kernel for loading OS/2 is being implemented now. WinNT can be loaded by chainloading the NTLDR. We decided to leave only multiboot support in base loader. Now L4, FreeDOS32, ReactOS and other multiboot compliant kernels can be loaded too.

The first FreeLdr programmers were Sascha Schmidt and Yuri Prokushev. They were planned to combine MicroFSD routines with GRUB's Multiboot specification, to allow L4 microkernel to be booted by FreeLdr. L4 uses GNU GRUB as default bootloader, and uses its features extensively. This time nobody of us was skilled in assembly language, and a FreeLdr project was stalled for a while because of one problem with MicroFSD functions.

Then, the boot project was dreaming, and development continued in other fields.

After some time, in summer of 2005, a new team member, Valery Sedletski (aka valerius) joins the project. He had a little experience in assembly, so, the problem was resolved soon. In the beginning of 2006, the FreeLdr can load multiboot-compliant kernels, and L4 microkernel was loaded. This time FreeLdr remains to be 16-bit. It uses native OS/2 MicroFSD routines directly. GRUB's multiboot routines were ported to 16-bits as well.

But then it was realized, that the 16-bit internals make more difficult implementing the loader extensions and access the whole machine physical memory. The 64k limitation makes it hard to use more than 64k in loader executable. We were planned to use MSDOS style executables first. As our bootloader was written in C with small amount of assembly code, the 64k could be reached soon. Then we decided to switch to FLAT 32-bits memory model and protected mode, and take GRUB scheme as a sample.

Then, in the beginning of 2007, the new 32-bit protected mode loader was started, almost from scratch. We were still reusing GRUB routines for base multiboot support. The GRUB filesystem support code was recomposed to be loaded as separate loader plug-in modules. (GRUB has all FS support code compiled-in. We decided to move it to a separate “blackboxes”). Also, we proposed to introduce the new kinds of blackboxes to support different transparent decompression algorithms (GRUB had ungzipping on-the fly support, which was compiled-in too), terminal access, executable formats support etc.

history

Which means that the loader is abstracted from OS boot sequence details.