From: noemail@basdxcqvbe.com   
      
   On Tue, 13 Jul 2021 15:56:12 -0700 (PDT)   
   "muta...@gmail.com"  wrote:   
      
   > But there is such a thing as an "option ROM". I'm not entirely   
   > sure what that is, but do even 10% or 1% of computers allow   
   > me to flash one of those?   
   >    
      
   This is just an extra ROM that comes on a insert-able expansion card.   
      
   It's inserted just like any other card, e.g., video, network, mouse,   
   com, etc.  It has a ROM with code on it, like the BIOS or Video BIOS.   
   Of course, the card will need the correct edge connector for your   
   generation of motherboard, e.g. ISA, MCA, PCI, PCI-EX, ...   
      
   For example, in the mid 1990's, there were option ROM cards which   
   extended or updated the BIOS, such as providing Enhanced Int 13h BIOS   
   ROM support or upgrade the BIOS for IDE drives.  You can also get them   
   for remote booting via the LAN.   
      
   IIRC, the BIOS detects a AA55h signature on a 2K boundary in the   
   address space for ROMs (Video, BIOS, Lan, etc) and calls a function   
   to initialize the hardware associated with the ROM.   
      
      
   From an old post of mine in 2012:   
      
   RP> PS/2 technical reference defines the use of the 0xAA55 signature   
   RP> for expansion ROMs.   
      
      
   From an old post of mine in 2009:   
      
   RP> As for 0xAA55 signature on 2k boundaries required for ROM's, network   
   RP> devices, PnP, etc., there numerous specifications that require that:   
   RP>    
   RP> "Microsoft Extensible Firmware Initiative FAT32 File System   
   RP> Specification", Microsoft Corporation, V1.03, Dec. 6, 2000   
   RP>    
   RP> "BIOS Boot Specification", Compaq Comp. Co., Phoenix Technologies   
   RP> Ltd., Intel Corp., Jan 11, 1996 V1.01   
   RP>    
   RP> "Plug and Play BIOS Specification", Compaq Comp. Co., Phoenix   
   RP> Technologies Ltd., Intel Corp. May 5, 1994, V1.0A   
   RP>    
   RP> "PhoenixBIOS 4.0 Revision 6", Phoenix Technologies Ltd., June 22,   
   RP> 2000   
   RP>    
   RP> "Novell Boot Rom Developer's Guide for DOS Workstations", July 9,   
   RP> 1992, V. 1.0   
   RP>    
   RP> Some of these also make changes to Int 19h and Int 18h boot order.   
      
      
   This old post of mine lists all the specifications I knew of at the time   
   which modified and extended the BIOS, especially Int 13h, 15h, 18h,   
   19h, and 28-bit or 48-bit LBA etc:   
      
   https://groups.google.com/g/alt.os.development/c/DTnX-lYbTHA/m/xrcQinFLEGkJ   
      
      
   --    
   The Chinese have such difficulty with English ...  The word is not   
   "reunification" but "revenge".   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)