User avatar
ncstebb

Posted Sun Mar 26, 2023 2:26 am

Apologies if this has been discussed already but...
Has anyone noticed this Amiga 1000 on Ebay. https://www.ebay.com/itm/385490630120

Quoting from the ad:
"This machine has 2 meg of chipram with original agnus and wthout expansion board. (See sysinfo photos)
This is proof that commodore was wrong in the maximum memory addressing that an original agnus could handle."


Looking at the photos it seems to have heaps of piggybacked RAM chips. Any ideas what the go is with this?

User avatar
dalek
Australia

Posted Sun Mar 26, 2023 5:18 am

It's not real chip ram. It's 512k chip ram and another 1.5MiB detected as chip but not
truly accessible by custom chips.

User avatar
blindguy

Posted Sat Apr 01, 2023 12:05 am

Guy is local and I went over and looked at it.
Hope the picts look ok.
20230331_185928.jpg
20230331_185042.jpg
20230331_185033.jpg
20230331_184718.jpg
20230331_184600.jpg
20230331_184522.jpg
20230331_184404.jpg

User avatar
nonarkitten

Posted Sat Apr 01, 2023 9:52 pm

To be clear, it is impossible to have more than 512KB of useable chip RAM on the Amiga 1000.

Yes, Kickstart will see any RAM in the $000000-$1FFFFF range as "chip RAM" but Skinny Agnus is only able to access 512KB, period. No ifs, ands or buts. Since Agnus generates the DMA, this means Denise cannot and Paula cannot either. There is 512KB of real chip RAM in that and 1.5MB of "slow fast" in the normal chip RAM region. This could cause compatibility issues if AmigaOS wrongly assumes all of this to be useable and attempts to put any bitplanes, audio samples, or what not into the extra 1.5MB of RAM.

This is based on a fairly well documented hack published in a magazine back in the day. You stacked RAM chips to hijack most of the signals and refresh but then rerouted the missing, higher address signals to use those chips. You got a 1MB system with them double stacked, and clearly, you can go to 2MB with four.

But it is NOT real chip RAM.

The CPU doubler looks like it's based on the work done on the Atari (I forget the name of it off the top of my head). It doesn't quite double the speed since some operations cannot complete any faster. I think it was closer to 50-60% faster, which I guess is still a nice boost.

User avatar
A1-X1000
Toronto, Canada

Posted Sat Apr 01, 2023 10:39 pm

holy mess of piggybanking :shock:

User avatar
McTrinsic

Posted Sun Apr 02, 2023 12:18 am

In the past, at one point I also owned such a system. For the the time back then this was an impressive hack.

Yes it gives more RAM.

No it’s not ChipRAM.

I am not sure but probably is something like RangerRAM / SlowRAM. As slow as the ChipRAM bus but only available to CPU.





Return to “Hardware”