EDX, where does BIOS put it.
Posted: Mon Aug 19, 2002 5:28 pm
This is just something I noticed while browsing through the intel processor docs.
Following a hardware reset, the EDX register contains component identification and revision
information (refer to Figure 8-2). The device ID field is set to the value 6H, 5H, 4H, or 3H to
indicate a Pentium? Pro, Pentium?, Intel486?, or Intel386? processor, respectively. Different
values may be returned for the various members of these Intel Architecture families.
I seem to remember that BIOS fills DL with the boot drive number, and all the interesting processor ID bits are stored in DX, so that makes it useless, but does BIOS store it anywhere? I think it's primarily to give information to a ROM chip if what I'm reading is right, but if it's stored it would seriously cut down the pain of detecting the processor family etc.
Tried to find it in HelpPC, but couldn't. Anyone got any ideas?
***
Just my luck, 2 seconds after I post I find a reference
.
Although it brings up a whole new problem. Is the value stored at F000:FFFE the family and model code from EDX or from a seperate BIOS detection routine?
Following a hardware reset, the EDX register contains component identification and revision
information (refer to Figure 8-2). The device ID field is set to the value 6H, 5H, 4H, or 3H to
indicate a Pentium? Pro, Pentium?, Intel486?, or Intel386? processor, respectively. Different
values may be returned for the various members of these Intel Architecture families.
I seem to remember that BIOS fills DL with the boot drive number, and all the interesting processor ID bits are stored in DX, so that makes it useless, but does BIOS store it anywhere? I think it's primarily to give information to a ROM chip if what I'm reading is right, but if it's stored it would seriously cut down the pain of detecting the processor family etc.
Tried to find it in HelpPC, but couldn't. Anyone got any ideas?
***
Just my luck, 2 seconds after I post I find a reference
. Although it brings up a whole new problem. Is the value stored at F000:FFFE the family and model code from EDX or from a seperate BIOS detection routine?