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Apple IIGS with Turbo->28 boot screen

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michaelsw

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Hi, all

Any one has idea on Apple IIGS ROM03 with boot screen first line "Turbo ->28" rather than "Apple IIGS"? Is it an early ROM03 unit, developer unit or pre-released ROM?
I couldn't find any information from the web and hope to get some help to identify.

Thanks,
Michael
 

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Thanks for the responses.
The boot screen picture was given by the original owner and I am yet to receive the unit. I will post more photos. There are only Disk drive interface, sound card and memory card but no accelerator card.
 
The Turbo->28 could very well be just another internal name for the rom3 IIgs. The IIgs has a 2.8Mhz CPU clock in "turbo" mode.
I had a small talk with one of the IIgs original rom developers who said that early versions of the IIgs ran at up to 14mhz with selected CPUs (unstable). The processor that WDC delivered was not consistent enough to allow more than 4mhz in the series production. Apple used a divider by ten to get the 2.8mhz. But as the ROM 3 has a new FPI (fast processor interface to connect the 1mhz Apple II to the 2.8mhz CPU/RAM) called the CYA (control your apple), there may be more to the rom... or it simply references the speedup due to rom optimization.
You should read the rom Image using a program or a physical device. And look if any chip in the IIgs has a different numbering than expected. Maybe you have a development version with special CYA?
It may be possible that Apple had added options for enabling faster cpu speeds... and never told anyone. It would explain the redesigned FPI->CYA. ... but I doubt that :)
 
I just realized, that the prototype of the ROM3 IIgs was called 'tenspeed' but I remember that turbo28 was also mentioned... I think.
 
rittwage said:
28MHz IIgs? nice hidden feature to the ROM3 if it were true.
Click to expand...

I don't think so. The 65c816 was only sold with speedratings of up to 10mhz at that time. But the early 65816 was a bugged design that tended to get unstable at higher speeds (>4mhz). The later (currently available) redesign of the 65816 in the late 90s is much more stable and allows speeds of up to 20mhz. Apple did not have a 28mhz cpu available in 1989... and 'tenspeed' is most likely just the chosen divider (28/10) 'tenth of 28'. It may be possible that there were tests with higher speeds when the rom3 was in development. The IIgs has an accelerator already installed to get the 'fast' 2.8mhz and also has the fast memory that can be upgraded to 8Mb. The IIgs is basically a IIe with preinstalled cards (graphics, music, serial and floppy) that has an accelerator with additional fast-memory. You could actually build a IIgs compatible IIe with expansion cards ;-) ... you would have to build a custom accelerator card with fast memory though. The IIgs uses shadowing and buffering instead of cache memory like the ZIPCHIP and Transwarp. The FPI (ROM1) has some modes that are very timing dependent (floppy access) but allow the access of 1mhz hardware at 2.8mhz cpu speed without slowdown. This is because one read access takes enough cycles to be buffered onto the 1mhz Apple II bus. The FPI/CYA is the gatekeeper that controls the access from and to the 1mhz bus. Since the Rom3 has the same memory slot as the rom1, many if not all memory cards would not be compatible if the speed of the cpu/fastmem was increased. The 'Mark Twain' on the other hand had tow normal 30pin simm modules and could have easily implemented higher memory speeds. But Apple never released a turbocharged IIgs with more than 2.8mhz, as far as anyone knows. If someone was cloning the FPI/CYA and design a new version, it would be possible to add other speeds. Fast memory could be a problem, since the expansion cards are designed for the 2.8Mhz CPU.

The FAST side has: CPU, fast memory and the FPI/CYA,
The SLOW has: 128k Slowmem, Audio, Video, Serial, floppy, ... everything else :).

The "Turbo ->28" is strange as well but it could simply be that "28" means "2.8mhz".

The higher speed tests i have heard about (4mhz, 7mhz and maybe 14mhz) were in the initial development of the IIgs in 1985. I suspect that the FPI/CYA are hardcoded to allow only 1mhz and 2.8mhz.
BUT ... i hope i am wrong :p

-Jonas
 
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Saying the ||GS is just a //e with other things tacked on isn't exactly right, in my opinion. It's really a whole different machine with a //e tacked on.

Granted most people only used them as a fast //e. At least that's what I saw in the early days. I don't think I ever saw one with a ROM3.
 
KC9UDX said:
Saying the ||GS is just a //e with other things tacked on isn't exactly right, in my opinion. It's really a whole different machine with a //e tacked on.
Click to expand...

It isn't that much of a different machine. You can remove the FPI/CYA and put a 6502 CPU directly onto the MEGA2 Chip. It would function as a Apple iie with a fancy graphics- and sound card. The GS is a true Apple II.

The funny thing ist that the Apple IIe graphics modes are still generated by the mega II and are fed to the VGC via a 4bit data stream. The VGC converts this into the video output. You can grab the original Apple II video (1bit data stream) from the Meag2 and add composite sync to get the original Apple IIe NTSC :) The VGC generates its own video modes that are fed through the memory refresh cycle. The funny thing is that the VGC is 'hardwired' to a fixed bank of 64k of the slow memory (//e side). This is the reason why the IIgs has only a single video page.

If you look into the shematics, you can easily see the separate parts of the IIgs. The CPU and fastmem are a separate entity from the rest of the system. The IIgs is a fancy //e with a built-in accelerator. It is maybe more close related to the //c if you look at all the pre-installed hardware. The IIgs is very different from a programming perspective, though. There are a lot of softswitches and registers present in the IIgs that are unique to this machine. The FPI/CYA maps several functions of the slow part of the computer into the fast part in a very efficient way. Some parts of the slow-mem are mapped into the fast-mem and even the floppy can be accessed without slowing down the cpu, even though the floppy is on the 1mhz part of the computer... Apple did a good job to integrate the old system with the new CPU. But this method of designing the IIgs has led to the problem, that the graphics access is actually very slow. The typical read-modify-write cycle is much slower than if the VGC were located in the fast part of the Igs

-Jonas
 
Any ideas as to why Apple did that for the system? Was it for 100% Apple II compatibility? Tying the IIgs's video RAM to fastram would have made the IIgs more pleasant for action gaming had they done so.

Wait, didn't they map the Ensoniq to 64K as well? IMO that really hobbled what you could do with the chip, and it's not like they had any Apple II compatibility to worry about...
 
retrogear said:
Probably a rom made during the development of the ROM 4 Twain which never went to market. Notice the similarity in the top header of the rom 04 source code which I assembled about 5 years ago.
https://www.callapple.org/vintage-a...iigs/analysis-of-apple-iigs-prototype-rom-03/

Larry G
Click to expand...

@retrogear: Very interesting :)
The 28 of the turbo ->28 could be the release number... -> Apple IIgs 'turbo' ROM release 28 maybe the ROM03 is actually ROM release 30 ? :p

@Trixter: I don't understand the thought process behind these decisions at apple myself. Maybe the IIgs was derived from bits and pieces Apple had already developed for the never released Apple IIx?

But I would suspect that the IIgs was designed to be able to access all the added functionality even in 8bit 6502 emulation mode since very few developers could actually program 65816 code at the release of the IIgs. This would allow software written for the //e to access all the added functionality of the IIgs without breaking the 64k boundary. You could use all the available development software for the A2 with the IIgs without modifications. But maybe a IIgs compatible graphics solution for the //e was planned (there was the Video Overlay Card in 1988 ) and maybe even an ensoniq sound card? Apple was always very secretive about these kind of decisions...

-Jonas
 
Also one of the design goals of the GS was to make sure it didn't outshine the Mac.
 
Trixter said:
Any ideas as to why Apple did that for the system? Was it for 100% Apple II compatibility? Tying the IIgs's video RAM to fastram would have made the IIgs more pleasant for action gaming had they done so.

Wait, didn't they map the Ensoniq to 64K as well? IMO that really hobbled what you could do with the chip, and it's not like they had any Apple II compatibility to worry about...
Click to expand...

The Ensoniq DOC's RAM was never directly addressable, everything with that chip is done via the Sound GLU chip. Don't know why the VGC's RAM was mapped to slow RAM. I guess it was to keep fast RAM completely free for 16-bit applications (remember this machine shipped with only 128k fast memory and 128k slow memory). There are some speed up tricks one can do with shadowing the VGC's RAM, but it can only do so much. The whole RAM shadowing thing was to keep onboard fast RAM contiguous with any expansion RAM, but allow timing sensitive 8-bit software to still run in the slow RAM and expect it at page 0 and 1.
 
I took some pictures of the unit. It is a ROM3 board with two hand-made ROMs, housed in a Woz limited case but without the label at the bottom. Most of the IC datecodes are 883X, and the latest is 8911. Will this just a hobbyist unit built with parts from multiple sources? or a developer unit?


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