From: muta...@gmail.com   
      
   On Saturday, October 23, 2021 at 3:22:14 PM UTC+11, JJ wrote:   
      
   > > For PDOS-generic, I will be doing BIOS calls to a special   
   > > BIOS that supports fread/fseek-like calls, and treats a   
   > > hard disk, or hard disk image, as just a flat file.   
   > >   
   > > It occurred to me that I should be able to point the BIOS   
   > > to an ISO CD image and allow the OS to fread/fseek over   
   > > that too.   
   > >   
   > > Is that something that a BIOS would be technically capable   
   > > of doing dynamically with a real CDROM?   
   > >   
   > > Thanks. Paul.   
      
   > Loading/booting an ISO file is the job of an OS. Not the BIOS.   
      
   I think we are talking cross-purposes, so I'm not sure if   
   El-Torito is relevant.   
      
   Let me try again.   
      
   Let's assume we have a real CDROM and a real hard disk   
   and a real BIOS, but I'm writing the real BIOS and I'm making   
   up my own specs for the BIOS, which OS vendors will need   
   to comply to.   
      
   Hard disks and CDROMs will be less than 2 GiB in size.   
      
   Rather than expose the OS to the concept of sectors, I'm   
   going to make everything byte-oriented. If you want to read   
   512 bytes, then do a bios->fread of 512 bytes, don't ask for   
   a sector. Sector size may not be 512 bytes anyway.   
      
   With bios->fopen, bios->fseek and bios->fread I am confident   
   that an OS will be able to call my BIOS and implement a FAT   
   file system.   
      
   With those same functions above, I am not sure whether an   
   OS will be able to read a normal/real CDROM.   
      
   I'm willing to add/subtract metadata on the fly in my BIOS,   
   but I'm still not sure a file system can be implemented. I'm   
   not sure if the OS authors will insist that they need a   
   bios->skip_to_track and bios->read_variable_sector or who   
   knows what else functions.   
      
   BFN. Paul.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)