Amiga OS 3.1 vs 3.5 vs 3.9 system difference

Question

I'm trying to find some resources on different versions of Amiga OS (aka Workbench) especially if there were any major changes to the OS architecture, resource use and drivers (with a goal to make CDTV use full extended RAM and CD ROM at the same time while on TF536 accelerator, known issue with conflicting memory addresses).

Workbench 3.1 was a major revamp to previous versions 2.04 (A600) and 1.3 (A500) both in terms of looks and performance. 3.5 added number of network and utility features, improved look and so on. Then we had 3.9 with boing packs, which included suport for more features, expansion cards, improved look, etc.

What about the underlying calls system makes to devices, drivers, how it manages memory? Is there any major difference there? Since 3.5 and 3.9 are modernised and RAM was more available at the time do they manage memory mappings differently?

Answer 1

One big improvement of 3.5 over 3.1 is the "big drive" native support (by patching ROM calls)

Without a separate NSD patch (new style device) installed, OS 3.1 could not handle drives bigger than 4Gb properly. Everything written after the 4Gb boundary destroyed the existing data by writing on the first sectors instead (the disk position was a 32-bit integer that only goes up to 4Gb, then wraps up to 0...)

So while this patch had to be (prorperly) installed to be able to use big drives on OS 3.1, OS 3.5 fixed that natively and ended hours of frustration.

Answer 2

From what I've read over time, AmigaOS 3.5 and 3.9 do not make any changes to the underlying operating system other than they now requires at least a 68020 processor.

AmigaOS 3.5 and 3.9 still rely on the Amiga Kickstart 3.1 ROMs which is where most of the code lives that handles the bits you're asking about (memory management, etc). The OS could have included patches to the ROM, but I am not aware of anything significant (certainly no virtual memory support).

The key thing is that regardless of the availability of RAM in the mid-to-late-90s versus 1989, the 3.x series ran on the "classic" Amiga hardware and thus hardware created for those machines most likely supported 3.1 if not 2.04. Remember, an A2632 board which came out around 1990 could be loaded up with 112MB which was a ridiculous amount for an Amiga 2000. I believe the PowerPC boards later could hold more, but a PowerPC Amiga is stretching the definition of what a classic Amiga is in the first place.