ZorOS Boot Manager

ZorOS is a boot manager that hides/shows partitions at boot time and allows to boot up to 10 primary partitions per HD


This is a little project, written in assembly (nasm), that perform a simple idea: boot several Operative Systems in fully separated disk spaces.
ZorOS is only a boot manager: it loads and execute only boot sectors. Further bootstrap operations are left at systems loaders.

Some features

ZorOS boot code is installed in MBR and in some sectors of track 0, beginning from sector 51 to 59, so this boot manager does not overlay other boot mangers. In absolute sector n.51 are stored 12 partition records and these partitions may be mapped in MBR, in any order, at boot time. With a reference text file, user-administrator can define partition size, boot order, menus, and real MBR partitions table shown at selected boot entry
A special feature performs a boot of etherboot ROM code, installed in track 0 (sect.4 to 50) and also a simple boot password is implemented.

How it works

As other boot managers, MBR code load additional code using standard int13 bios call. The full code is then relocated and executed. The program performs some check, adjust partitions table (only if necessary), load, check and exec boot record as defined in reference file. For partitions allocated beyond cyl 1023, the program uses extended disk bios call, of course, so disks up 2TB are supported.


Latest release is 2.6 (update: Mar 03 2009), available here to download  md5sum


03/03/2009 - first public release of software
02/28/2009 - improved installer, .asm sources, so size of binary code is reduced below to 4k

How to install

To configure and install binary code, an additional program "zorox" that integrates a simple text editor, is used to calculate partitions values, insert menu items, timeout reference and other user-parameters in boot code; "zorox" program is also a fdisk-like tool and binary disk editor.

Missing features, known bugs

- At this time "zorox" installer will only work with standard disks (255 head, 63 sectors), so old disks and small size USB-stick may be not well supported
- Integrated editor may not work properly in some circumstance; you can use external editor instead "zorox" installer
- In reconstruction of ZorOS partitions stored in track 0 and next recompilation may occur some errors in partitions sizes, due numeric round. Pay attention in this case and check results before install.


The development work will proceed to improve installer, change boot interface, and implement some additional features as boot from CD.
To join this project, please contact the project administrators of this project, as shown on the project summary page.


Boot messages are now available in English or Italian, but ZorOS may be full configured regards messages. Using only standard ascii text, there are some limits to implement messages with accented chars.