WIN XP and DOS Emulation

This supports my contention that most BIOS's setup the machine to look like a basic PC (actually about AT class) before trying to boot the machine from disk.

Many BIOS's such as the one I'm using right now work more like the PC XT to get the boot done. It uses the "game cartridge" detection by searching for IIRC A5A5(IIRC)[1] at the start of a memory page. It finds the PROM of the video card to get the video started and strangely enough part of the very same PROM that is doing the searching to get the first version of the disk operations going. =A0

The first version of the disk code is just smart enough to load the master boot record that then gets GRUB started. Only after GRUB has started the OS is the whole disk seen. During booting, it is confined to the first 1024 tracks because the BIOS code uses a 10 bit value for the track.

My XT machine supports external ROMs. The documentation (which I finally found online, and is quite well specified) states:

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The ROS checks for external ROMs between addresses C0000 and F4000 in 800h (2k) byte increments. An external ROM which conforms to the following specification will be initialised by the ROS:

1. The first two bytes contain the hexadecimal value 55AA.
2. The next two bytes contain the size in 512 (1/2K) byte increments.
3. The next byte is the initialization routine entry point.
4. The LS byte of the byte sum of the ROM is zero.

When a ROM conforming to this specification is located then the initialization entry is called.

If the checksum test fails then an error message is displayed and initialization is not called.

The IGA BIOS ROM conforms to above standard and if it is enabled, it is entered (at C0000)...

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So the ROS (Resident Operating System, i.e. the BIOS startup code) initializes whatever's found (which, in my case, includes the hard drive controller's BIOS and the IGA (Internal Graphics Adapter, which is high resolution EGA with a whopping 256k RAM)). I could, in principle, burn an EPROM that conforms to these specifications and run my own programs instantly on startup.

Tim

w.

I am going to give that dosemu program a try. My understanding is with linux you can get a fast response to interrupts IF you own the port. That means either running a root or chowning the device. [No first hand experience here, just what I read.]

Or save yourself a lot of hassle and buy an ASUS mobo. Oh wait, it just boots to linux and you may not want that.

ASUS makes XT mobos that boot to linux? Cuz that's what I thought we were talking about. ;-)

Tim

I think so. See this also:

have fun.

Doesn't look XT to me.

Tim

If they had been in the business back then, it would have to load it from hard disk. I had my i teeth crossed.