Questions for someone who knows some about ram and roms...

[zektor]

I don't know why I didn't notice this until today. Some time back I popped my 1.3 kick rom out of my A500 (rev 6a) and popped in a 3.1 kick rom. It was a great update and I specifically did it for two reasons. One being the ability to boot from external drives, and the second was the ability to easily switch to PAL mode.

Well, I have been messing around with the old demos I loved when I was a kid, and played "Vision Megademo 4" the other day after years. Today I was cleaning up and removed my Supra Ram 500RX (which has 2MB onboard) and ran the demo without the ram. The system itself has a 512k ram expansion in the trap door of course. Well, the demo would not run (booted to the decrunching stage and stopped)

I then booted into workbench and realized that chipram is reported as 1MB and other mem (fastram) is reported as 0. I popped the ram expansion back on and of course the demo works fine.

This is obviously because of the rom upgrade. I know I ran this demo without the SupraRam in 1.3. I just want to make sure that this is normal. I never went past the default 1.3 on my old A500, so this was sort of a new venture for me. I guess 3.1 rom just NEEDS more memory than the 1MB (512k + 512k trapdoor) that most A500's usually had?

[zektor]

Aha. This must be it. So, either keep my good old A500 and SupraRam with 3.1, downgrade back to 1.3...or get a stronger machine I'm fine with what I have now, but a new machine is in my sights.

[zektor]

Yeah, but this particular demo works fine in 3.1....as long as the fast ram is present. It is just odd how 3.1 applies all of the internal and trapdoor memory on the A500 to Chipram. You know, I tried to kick down to 1.3 and then boot workbench...and it only shows 512k of memory. I know that is off topic, but still kind of odd.

Basically, as soon as 3.1 was installed, all of the memory inside of the machine became chip memory, with no fastmem present. The demo must need some fastmem, which is why it only works with the SupraRam side expansion adapter in place.

I have another A500 and another 3.1 rom I will test tomorrow and see if it reacts in the same way.

EDIT: I think I have partially found my answer...from Wikipedia:

"All versions of the A500 could have the trap door RAM configured as Chip RAM by a simple hardware modification, which mainly involved fitting of a later model of AGNUS chip."

Apparently the 3.1 rom I had installed has "moved" my trapdoor ram to Chip ram without any other hardware modification otherwise. I did not replace the AGNUS however.

[zektor]

Well, that reply does not help. If you say it is not possible, WHY is it not possible? Possible or not, this is exactly what has happened on my end.

This is the setup btw:

Amiga 500 rev 6a
MicroMegs 512k ram expansion in trapdoor
1.3 rom swapped out with 3.1 rom pulled from an A2000
SupraRam 500RX w/2MB onboard

Only thing(s) I ever did to the system were replace the clock battery on the MicroMegs and install the newer kick rom.

I would guess that Daedalus hit the nail on the head with 3.1 applying the memory to a different address. It seems like a logical explanation.