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AmigaOne - SLB

SLB is an abbreviation for Second Level Booter, and is code that is executed on completion of the U-Boot process to provide dual-booting and other options, including loading the kick-start process for the OS4 system. For this reason it is sometimes referred to as the "A1boot loader".

On a Classic Amiga, the Kickstart ROM contained the basic libraries such as Exec, Dos, Intuition, etc and this made it possible to boot using a disk with no Operating System installed. Booting without the Startup-Sequence still allowed you to use a basic Shell to do "first aid" on your system.

On the AmigaOne U-Boot initialises the hardware and boots an operating system but it doesn't have all of the libraries needed to boot the AmigaOS. It doesn't allow you to boot without Startup-Sequence like on the Classic. It does, however feature key components such as ExecSG, FFS2, etc which are stored on disk and must be stored in the SYS:Kickstart directory. The advantage of this system is that it's now possible to update the OS just by updating one of these modules. On the other hand it is easy to break your boot partition leading to a non-bootable OS with a wrong library version, missing module, etc.

We have read that the SLB makes use of GPL code for the ext2/3 reading routines (taken from GRUB), but is a bit smarter as it isn't just using routines from GRUB, although it is based around the same idea. Having said that, the SLB itself has no GRUB code to load Ext2 or anything else. The GRUB code lies within UBoot and SLB simply calls it. That is why when upgrading, you must upgrade both, otherwise bad things will happen.

It is currently only useful if you use RDB partition maps, but technically it could reside in an MBR as well, but it isn't very useful without U-Boot, because it has to know where to find it. It is smarter than GRUB, because it understands both Amiga and Linux filesystems, and will merge the two menus together so that you only need to edit the Operating System's own menu file to update one of them. Add a Linux kernel, and Debian can edit the Linux menu file. Add a new OS4 kernel, have Installer edit the AmigaOS menu file. A lot more flexible than most dual-boots on x86.

Disclaimer: Amiga Auckland have prepared the above information for the use of its members based on our experiences and as such is subject to revision at any time. Amiga Auckland cannot guarantee any of the information and cannot be held accountable for any issues that may result from using it.


Copyright 2005 Amiga Auckland Inc. All rights reserved.
Revised: September 26, 2005.