User:Johnburger/Demo/Pad/ISO/Catalog

This Sector is where the "magic" happens. It defines the very first Sector on the CD as the default Boot Sector, and for the BIOS to treat the CD as a Floppy Disk.

It is only because ISO 9660 treats the first 16 (2 kiB) Sectors as "reserved" that this trick works: since the BIOS looks for the Primary and Boot Volumes from the 17th Sector, we can put whatever we like before it:

• This Demonstrator;
• A complete OS;
• A loader for the rest of the CD, perhaps with an ISO driver;
• Anything! Over to you...

Demo/Pad/ISO/Catalog.inc

;
; Pad/ISO/Catalog.inc
;
 
; This file defines the Boot Catalog Sector for the ISO image. This basically
; points to the first sector, which is where the standard boot sector is anyway.
;
; Note that ISO.Boot.Default.Media has been set to Floppy.1440. This option
; works for VMware, VirtualPC and VirtualBox. Other options work for VMware only
 
%define         ISO.Catalog.ID          Version.Author
 
ISO.Sector.Catalog   EQU                ISO.Sectors
%assign              ISO.Sectors        ISO.Sectors + 1
 
ISO.Boot.Catalog:
 
; Add Validation entry, and calculate Checksum for us
ISO.Boot.Validation ISO.Validation      ISO.Catalog.ID, ISO.Boot.Platform.x86
 
ISO.Boot.Default:
.Bootable       DB              88h
.Media          DB              ISO.Boot.Media.Floppy.1440 ; HardDisk ; NoEmulation
.Load           DW              0000h   ; This could be 7C00h. 0000h defaults it
.System         DB              00h
                DB              0
.Count          DW              1       ; You can use this to load MORE!
.LBA            DD              0       ; Start sector to load
.Reserved       TIMES           (1Fh-0Ch+1) DB 00h
 
ISO.Boot.Catalog.Padding EQU    ISO.Sector.Size - ($ - ISO.Boot.Catalog)
                TIMES           ISO.Boot.Catalog.Padding DB 00h