In recent weeks I've been implementing the full range of Acorn System machines. These are basically a collection of Eurocards each for CPU, RAM, VDU, etc. on an Acorn Bus backplane.
Acorn System 2 (acrnsys2):
This system consists of 6502 CPU, 8K RAM/ROM, cassette, and 40 column VDU cards. This is a cassette only (Cos) machine. It should also contain a 4K BASIC ROM but is currently MIA, though I hope to find this during an Acorn meetup at Centre for Computing History in September.
Acorn System 3 (6502 CPU) (acrnsys3):
There are very few floppy images out there for these machines, though this appears to be the System 3 Utilities disc containing Floating Point BASIC to run from RAM.
I've made each card a slot device, and this System 3 has 2x8K Static RAM boards, 40 column VDU card, and a FDC. Each 8K card also has two ROM slots for extensions such as BASIC, Econet. I currently only have Econet ROMs which will be softlisted for these slots.
The memory boards have links that determine where RAM/ROM is addressed.
Acorn System 3 (6809 CPU) (acrnsys3_6809):
This was already in MAME but has been rewritten as a collection of slot devices, and added a FDC to the system to run FLEX. I've renamed a6809->acrnsys3_6809 to match other machines in the range. The 40 column VDU card cursor was incorrect, and is now rendered by the 6845. The FLEX floppies are currently MIA but again hope to get them imaged in September.
Acorn System 4 (acrnsys4):
Basically the same as System 3 but with more slots and comes with 2 floppy drives as standard.
Acorn System 5 (acrnsys5):
The System 5 was the last in the range and had some improvements with a 6502A (previous were 6502), 32K RAM boards, 80 column VDU, etc. It seems it was also used to develop what became BBC BASIC, and we have an image of it.
The 32K RAM boards also have links to select where they are addressed. The 80 column card can also be re-mapped for use in a 6809 system.
The System 5 would usually contain an Econet card and be used as a File Server, and this is handled too.
The Acorn Atom has two Acorn Bus expansion ports (internal/external) so am also moving it's floppy implementation to slot devices, and adding other expansions.