What Needs to be done for a NeXT Emulator

[andreas_g]

@rory040
Thank you for pointing me to that potential issue. I will fix it with the next release.

I wonder if we could artificially increase the RAM size on Previous. I think it's currently limited to the maximum ram of both the motherboards chip density of its time on both the computers and NeXTdimension.

I think the current maximum is 128MB.

Is doubling that amount a problem?

I know NS 3.3 and OS4.2 could do more than that under intel. Not sure if there is some kernel limitation on black hardware?

Unfortunately this is not possible. There is just not enough address space in black hardware. The 4 GB address space is split into 16 parts of 256 MB each. Theoretically black hardware could consist of 15 boards on the NeXTbus and one shared space. Of course there is no hardware supporting this, but the logic has been designed that way.

The 256 MB address space of a single board needs to hold ROM, RAM, VRAM and device addresses. Therefore it is not possible to use the full 256 MB for RAM only. 128 MB is the maximum on Turbo systems, 64 MB is the maximum on non-Turbo systems and early NeXTstations are limited to 32 MB through the amount of accessible memory banks.

[cuby]

Would it be possible to build a NuBus memory board for Cubes? There were a number of memory boards for NuBus Macs, but it seems these were mostly used as RAM disk:

https://68kmla.org/bb/threads/daystar-nubus-ram-expansion-board.19909/

The MacIvory (Nubus-based Lisp machine) seems to use a NuBus memory board, but I'm not sure if this was exclusively used by the Lisp CPU and not the 68k:

https://www.typewritten.org/Projects/Symbolics/463.html
https://github.com/jaoswald/ns816-declrom

[ZombiePhysicist]

As far as I know in theory it should be possible. The nubus was supposed to be a dumb bus allowing any combination of full on motherboards. In someway we had that. You'd cut the trace on the nubus and put in an 030 board with your 040 board and run them in parallel. Hook them up via ethernet and DPS remote into the other machine. Bit of a kludge but you could use Zilla with it. 

Let's see there were DSP boards, one that had 5 on it. 

NeXT dimension which really was it's own coprocessor with ton of video ram and the bus was 'fine' for moving stuff across (was a bit laggy slow but it's old tech).

I forget what other kinds of cards were available, I know a few more, but I think they were more scientific.

TLDR yea, the NeXTdimension kind of did this already. Not clear how you map the addresses across the NuBus without some kernel hack though.

[itomato]

Check Appendix A of NextBus_Interface_Chip_Specification.pdf:

Figure A-1 shows a schematic of the sample memory board implementation. An underscore in front of a signal denotes active-low. Note that this schematic is provided as a sample only; the memory board has not actually been built and tested.

[celluloid]

On August 16th 2010 a user named cjbriare started a thread with the same title in another forum. This is where the story of the first NeXT Computer emulator "Previous" began.

hey, it's me, cjbriare

I am completely amazed that this thread lives on. No idea my post out of pure curiosity as a teenager would bloom into something alive. Absolutely love this community and its growth + Previous' growth!

Thanks for the shoutout and thank you all for your contributions.

Also, is this where the NeXT nerds hang out now? is nextcomputers.org still active?

[Rhetorica]

@celluloid We'll keep on NeXTing to the end of time, yes we will! It's great to have you here.

This is a bit off-topic but it deserves to be recorded here as much as anywhere else, so...

Unfortunately the old forums had to be abandoned after a series of dictatorial moves by the administrator there made it clear he didn't care about the health of the community nor even the integrity of the historical record. At least three people got banned and our posts subject to damnatio memoriae without warning, for crimes including, "attempted to organize a chatroom," "linked to pictures posted on Imgur instead of using forum attachments," "shared too many betas," "attempting to archive the site," and, worst of all, "protesting that someone got banned," which was the nail in the coffin that led to the entire development history of Previous being deleted.

The official reasons given for these actions were half-truths at best, and accompanied by furiously adding new rules like "don't make overly long posts" that seemed to be purpose-built to provide excuses for further arbitrary verdicts—and in case there was any doubt about the freedom of speech on the forums, they were then put into moderation mode, requiring administrative approval for each post. Understandably this was poorly-received, and the membership of the aforementioned chatroom ballooned as a result.

nextcommunity.net was founded in the aftermath with the promise that we would do everything possible to keep it pluralistic, inclusionist, high in bus factor, available as a hosting service, and willing to adopt new tech and culture as needed to serve and celebrate the hobby. There's still a long way to achieve all those goals (e.g. the site still has a bus factor of one) but we do at least have multiple forum admins and an open sign-up policy, which is a lot more than the old site had, as far as I know.