Maximum amount of RAM for a 32-bit Amiga

[redblade]

I read on https://retrocomputing.stackexchange...a-or-commodore that the maximum amount of memory is 1024MB using 4 Zoro III expansion slots each with 256MB RAM on a big box amiga? Is this the maximum out of 4096MB? I know Kickstart takes 0.5MB RAM, Custom chips take so much...

Is it possible to design a 32bit cpu i.e a 68EC030 to use 3 or 3.5GB RAM?

Do you have to run a

setpatch

to modify exec.library to modify the RAM memory lists?

I know you must be wondering what you would have in a 3.5GB RAM amiga, maybe in the old days you would store a WAREZ BBS there so if you got busted all the evidence would go. Or maybe you would just use it for look up tables for programming, I don't think the sine/cosine table took up much RAM for the old 3D cubes. (less than 4k??)

Maybe this type of memory would allow faster INT calculations compared to Doubles/floats as you would have more memory to play with
Thanks.

[a/b]

Going over 2GB means that the "negative" $80000000-$ffffffff range is accessible and that would break a lot of software, including ROM. Next, you have exclude the hardware and special purpose regions under $10000000, that's another 256MB.
So down to 1.75GB (plus chip memory and a little extra you could stuff into Zorro2).
Then you have to consider the number of slots for memory sticks, eventual constraints related to that, etc. to see how much you can actually fit.

[thebajaguy]

The Amiga memory map, as defined in the OS design, does not use the upper 2GB for any address. Think of it as the limit of a signed 32-bit integer, with the Most Significant Bit equaling negative values, and off-limits for programs.

There is the hardware Z3 AutoConfig detection 'slot' up at the top of the memory map, but any card which appears there will be assigned to the Z3 AutoConfig pool in the legal space.

Technically, your only option for 'more' memory to run things is to look into Virtual Memory (which is really RAM swapped to disk). The program(s) get a large memory model that would technically overlap if all were in use. Performance impact would certainly apply, too.

[Hedeon]

Expansion.library limits stuff from 0x40000000 to 0x80000000 for Z3 autoconfig too, I believe

[Toni Wilen]

At least 3.1 and earlier didn't have any limit checks and allowed Z3 RAM over $80000000 limit. This config can be created in WinUAE without any unexpected side-effects. Later KS versions (not sure if 3.1.4 or only 3.2) restrict it like OS4 which is annoying

[tomcat666]

real A1200 with pistorm32 and rpi4 with 4Gb of ram (amiga limited to 2Gb) :

[mschulz]

Originally Posted by Toni Wilen

At least 3.1 and earlier didn't have any limit checks and allowed Z3 RAM over $80000000 limit. This config can be created in WinUAE without any unexpected side-effects. Later KS versions (not sure if 3.1.4 or only 3.2) restrict it like OS4 which is annoying

There is at least **ONE** function in exec.library which will break if there is more than 2GB of RAM available - AllocEntry. The problem with it is, that AllocEntry is using the most significant bit to report a failure. There are probably other places which could misuse the MSB in similar manner. For example, ExecBase->ResModules is using array of pointers to Resident structures instead of regular list. The arrays are chained together in a way where the MSB indicates if the pointer is to Resident (MSB==0) or a pointer to another array of pointers (MSB==1).

This is very unfortune, because otherwise there would be no problem with having more than 2GB of memory classic AmigaOS...

The sad thing is, both cases would be non-existing if AmigaOS creators would have picked the LSB instead of MSB. That would not harm at all because:
a) All memory allocations are aligned to 8-byte boundary (size of MemChunk struct) anyway
b) An array of pointers to Resident has to be aligned on 2-byte boundary since 68000 cannot read LONG from odd-aligned address.

[Toni Wilen]

I know. But that can be worked around easily enough (if you get bit 31 set, use some other way to allocate it) without bothering everyone with "too much" memory.

[Lord Aga]

Originally Posted by redblade

Is it possible to design a 32bit cpu i.e a 68EC030 to use 3 or 3.5GB RAM?

I see someone decided to finally make a decent Final Fight port

[Don_Adan]

For me exec.library in Amiga OS 3.3 or Amiga OS 3.4 can be extended (new LVO's) to support memory from $80000000-$ffffffff range, even if it will be special memory, used only for data streaming/handling. WinUAE can be used for tests. Same for support files bigger than 2GB. Old LVOs can be updated for checking ID (f.e "48bt" or "64bt") in D1 (word or highword) or new LVO's can be added. And new created programs can handle big files.

[meynaf]

Originally Posted by redblade

Is it possible to design a 32bit cpu i.e a 68EC030 to use 3 or 3.5GB RAM?

You don't need to change anything cpu wise. 68030 itself can access 4GB with no problem (actually it would be even more if its FCx pins were used).
The limit is really the OS (and not a big part of it).

[redblade]

Thanks guys, was just wondering if there were going to be RAM accelerators with 1GB or 2GB RAM sticks

[qz3fwd]

Originally Posted by redblade

Thanks guys, was just wondering if there were going to be RAM accelerators with 1GB or 2GB RAM sticks

I read somewhere that the accelerator card bus/slot specifications limit CPU accelerators to 128 MB local RAM?

[Daedalus]

The A3000/A4000 memory map allocates a maximum 128MB for the accelerator slot, and no accelerators back in the day exceeded this, even when their A1200 counterparts did (Blizzard A1200 accelerators support 256MB). However, I believe the upcoming TF4060 goes beyond 128MB by allocating extra RAM above 128MB as Zorro-III RAM instead.

Realistically though, so long as it's cheaper or easier to not fit or support multiple GB of RAM, I can't see why any accelerator builders would do so. The time of heavy serious use that would need that much RAM is long past, so other than having a bigger number in the title bar, I can't see how there would be any significant demand for 1GB or 2GB accelerators.

I had 256MB in my A1200 (which was my main computer well into the '00s), but downgraded it to 192MB many years ago and never bumped into that limit.