AmigaOS 3.9 on A2500?

[PotatoBox]

Hello,

I've recently acquired an Amiga 2500 that has a A2630 (25mhz 030) with I believe ram maxed out considering there is also a A2058 RAM card and 2MB ram on the A2630 itself. Not sure as I have to check the jumpers. How does ram work on an Amiga anyways? So from what I read, there is chip ram and fast ram. Now, what ever ram that is added in to the Zorro slots is fast ram and whatever is in the motherboard is chip ram? This computer also has an A2091 in it too. There is a video toaster in there too and also some other video production stuff I'm but not worrying about that right now.

Would this setup be suffice to run AmigaOS 3.9 smoothly or should I just stick with 3.1?

[Matt_H]

Welcome! It sounds like you are fairly new to the Amiga?

Broadly speaking, chip RAM can be accessed by the CPU or the custom chips. Fast RAM can only be accessed by the CPU. Chip RAM is traditionally used for audio and video data, the things that need to be processed by the custom chips (e.g., sound and graphics) and fast RAM is used for everything else.

Fast RAM is called fast RAM because it's usually faster than chip RAM. But there are actually several different kinds of fast RAM.

So-called "slow RAM" is the same speed as chip RAM but can't be accessed by the custom chips. A very small number of old games are hard-coded to require slow RAM. Only some A500s and early A2000s shipped with slow RAM. Some simple motherboard modifications can turn slow RAM into much more useful chip RAM.

16-bit fast RAM is what's available on the 2058 board (and the 2091 if its RAM sockets are filled). 16-bit RAM is limited to a total of 8MB, via the Zorro II bus. It's usually faster than chip RAM, but not by much.

32-bit fast RAM is where you start seeing serious performance boosts. You can get 32-bit RAM on 68020 and higher accelerator cards. I believe it's limited to 128MB.

The 2630 that shipped in the 2500/30 is a bizarre design in that it uses 32-bit RAM that is mapped into the 16-bit address space. In other words, you'll get 32-bit speed on the 2630, but it will use up part of your 8MB limit.

It sounds like you only have 4MB of RAM in your machine - 2MB on the 2630 and 2MB on the 2058. Technically, that meets the requirements for 3.9, but it's not going to leave you with much RAM left over. I recommend sticking with 3.1 on such a setup. I run a similar rig with 4MB on the 2630 and 2MB on the 2091. Resources are tight, so I'm happily keeping it on 3.1.

[Oldsmobile_Mike]

I would get the full system specs and compare them to the list of minimum and recommended requirements for 3.9 (just saying that since you seem to not know exactly what is installed).

http://os.amigaworld.de/index.php?lang=en&page=8

Also someone else just posted a similar thread on this yesterday: http://www.amiga.org/forums/showthread.php?t=72504

Some good info in there already. Good luck!

[psxphill]

So-called "slow RAM" is the same speed as chip RAM but can't be accessed by the custom chips.

The hardware reference manual 3rd edition calls it slow.

http://amigadev.elowar.com/read/ADCD_2.1/Hardware_Manual_guide/node00D3.html

Fat agnus was changed to support 1024k of dram, but they didn't change the address register widths in the dma engine (probably to save time/cost). I believe it was a way of trying to stop Jay Miner going on about the ranger prototype, where the additional memory 1mb ram was actually fast (I'm not exactly sure where it was mapped). In the Amiga 3000 memory map they label the 512k area @ c00000 as Ranger RAM.

The 2630 that shipped in the 2500/30 is a bizarre design in that it uses 32-bit RAM that is mapped into the 16-bit address space.

It's not the bizarre. RAM was still expensive and having it possible to DMA into your 32bit RAM from another ZorroII card is pretty useful. I don't think 32bit memory moved out of the 24bit address space until the A3000 brought Zorro III.