The C128 and Z80 CPU ...or Intel 8088?

[Iggy]

A cheaper 8088 or 8086 processor would have provided CP/M-86 compatibility, and MP/M-86 compatibility with a possible upgrade to Concurrent DOS if CGA/VGA compatibility was implemented via a VLSI.
When the C128 was in its planning stages custom chips were becoming quite common.
While the earlier chips in the C64 and Amiga required a large investment to create, the latter custom chips in devices like the Tandy 1000 and the Color Computer 3 were significantly less costly.
AND as Commodore owned MOS...the C128 wasn't a particularly adventurous design (and for that matter Bill wasn't that great a designer).

[psxphill]

Impossible? Nonsense.
My firm made the PT68K4 PC compatible with a V20 based board.
The Amiga could be made PC compatible with a series of boards that topped out with a '386 based board (and those have a much better resale value than PCs based on the same processors).

In 1985 you would need register level CGA/floppy/dma/irq/serial etc. You couldn't reuse anything from the C64, so it would essentially be a PC and a C64 in the same box (like https://en.wikipedia.org/wiki/Amstrad_Mega_PC).

The Amiga at least could display the video from a PC using it's graphics chip, so a combined hardware and software approach allowed it to work. But to make it compatible with games you had to use an actual ISA graphics card. So it was just an Amiga and PC in the same box, it didn't really save any money and you could get better PC's.

Sure you could stick an 8088 in the C128 and it would have access to 64k at a time. No software would know how to display anything on the screen or access more than 64k. The original PC came with 64k so you could run software that worked on that as long as it only used BIOS and DOS calls to access hardware (which a lot of software didn't).

The Z80 came quite late in the C128 design, so there was never a time when it would have made sense to design something radically different with an 8088 that allowed more than 64k at a time.

Of course everything is possible given enough time and money, but keeping to the C128 selling price and spending very little in chip design and it was impossible.

[glitch]

@Rabbi:

    Thank you for the AmigaZ80 link!  That will be fun too.   I am actually in the process of upgrading the RAM on the Model 4P to 128K.  I am in the process of getting it ready for sale on eBay (shameless plug if anyone is interested...)  and wanted some additional disks to include.  I downloaded some other LS-DOS disk images and even blew the dust off my old high school books and entered some lines of FORTRAN to test out the compiler I found.

I learned FORTRAN on an old PDP-11 - THAT my friends was pain.  Our teacher as brilliant as she was, wanted us to learn to code on cards and enter them with a card reader and output would be sent to the teletype.  We then switched to the terminals - at least that was easier to debug.  After that we switched to the lab full of CBM PET machines.

[Iggy]

In 1985 you would need register level CGA/floppy/dma/irq/serial etc. You couldn't reuse anything from the C64, so it would essentially be a PC and a C64 in the same box (like https://en.wikipedia.org/wiki/Amstrad_Mega_PC).

The Amiga at least could display the video from a PC using it's graphics chip, so a combined hardware and software approach allowed it to work. But to make it compatible with games you had to use an actual ISA graphics card. So it was just an Amiga and PC in the same box, it didn't really save any money and you could get better PC's.

Sure you could stick an 8088 in the C128 and it would have access to 64k at a time. No software would know how to display anything on the screen or access more than 64k. The original PC came with 64k so you could run software that worked on that as long as it only used BIOS and DOS calls to access hardware (which a lot of software didn't).

The Z80 came quite late in the C128 design, so there was never a time when it would have made sense to design something radically different with an 8088 that allowed more than 64k at a time.

Of course everything is possible given enough time and money, but keeping to the C128 selling price and spending very little in chip design and it was impossible.

Ah! My apologies. You guys are frequently good for some education.

"The Z80 came quite late in the C128 design..."

That explains SO much.
I've always blamed Bill for the kludged together nature of the C128.
Its like they tacked a cheap CP/M board onto an existing design, which appears to be what happened.
I'd always thought that was what Bill intended at the outset.
Which should explain my bad attitude about him.
He and Dave must have felt a constant sense of butt hurt dealing with Commodore's management and their perpetual penny pinching.

They probably should have just left the Z-80 out (or the 6502).
If you compare the C128 to something like an MSX system, the C128's implementation of the Z-80 processor comes off looking really lame.

[matthey]

The C= 128 should never have existed as late as it was (less than 1 year before the Amiga in early 1985). C= should have put a SID chip in the Amiga and paid to have a highly optimized C64+6502 emulator written in 68000 assembler. Perfect upgrade path to the Amiga plus the SID adds new sound synthesizing functionality to the Amiga.

[psxphill]

The C= 128 should never have existed as late as it was (less than 1 year before the Amiga in early 1985). C= should have put a SID chip in the Amiga and paid to have a highly optimized C64+6502 emulator written in 68000 assembler. Perfect upgrade path to the Amiga plus the SID adds new sound synthesizing functionality to the Amiga.

I love SID tunes, but I'm glad that the Amiga had Paula. A full speed C64 emulator with decent compatibility on a 68000 Amiga is impossible..

The C64 lived on for another 7 years, so there was definitely a market for an 8 bit computer. The C128 just turned out too expensive and not enough people cared about C128 or CPM mode.

He and Dave must have felt a constant sense of butt hurt dealing with Commodore's management and their perpetual penny pinching.

I'm not sure that Bil was that bothered about the penny pinching, he seems to quite enjoy the challenge. The problem at that time was marketing, the 8563 chip designer and his boss who cancelled the C128 because it was taking too much time. If Jack had stayed then these problems would have resolved themselves with much less impact to the C128 schedule.

Without Bil you would have got this instead http://www.floodgap.com/retrobits/ckb/secret/d128.html An evolution of the P500 that was dropped because commodore needed as many VIC and SID chips as they could make to stuff in C64's.

The C128 with just a z80 would have been a disaster. After the C128 shipped someone worked on an upgraded design that could run the Z80 faster. I don't know if that ever survived and whether it would be practical as a retro-fit.

[matthey]

I love SID tunes, but I'm glad that the Amiga had Paula. A full speed C64 emulator with decent compatibility on a 68000 Amiga is impossible..

Paula and SID both are possible without too much overlap in functionality. It is very easy to throw an FPGA SID (or 2) in an FPGA Amiga motherboard now days if it would sound acceptable as all digital. SID in an Amiga back then would have probably required lowering the voltage more but that was happening with later revisions of the C64 anyway.

I believe the 68000 could have emulated the 6502/6510 CPU o.k. but the chipset emulation would have been difficult at full speed. The Amiga has its custom chips to offload the 68000 so maybe it would have been good enough. Perhaps the biggest hurdle at that time was the buggy AmigaOS. Different size and capacity of floppy drives didn't help either.

The C64 lived on for another 7 years, so there was definitely a market for an 8 bit computer. The C128 just turned out too expensive and not enough people cared about C128 or CPM mode.

I would have continued to manufacture the C64 until demand dropped too much. Developing and marketing the C128 was a waste of resources which could have been used for the Amiga.

[psxphill]

I would have continued to manufacture the C64 until demand dropped too much. Developing and marketing the C128 was a waste of resources which could have been used for the Amiga.

According to google, in 1985 the C128 was $300 and the A1000 was $1295.

There was room in the market. If anything they should have stopped selling the C64 and cost reduced the C128 (which they started doing but then cancelled it and kept selling cost reduced C64's instead).

[Iggy]

I am not sure I would not have favored a 2MHz 6509 with no Z-80.
Faster operation just makes sense.

For that matter, if you eschew compatibility,  Commodore could have used a 2MHz 6809 which has a lot of advantages over a 6502 based CPU.

One of my primary reasons for favoring the Amiga is that system's use of a decent Motorola processor.
I have never been that impressed with MOS' cut rate offerings.

[psxphill]

I am not sure I would not have favored a 2MHz 6509 with no Z-80.

Accessing memory with the 6509 was a nightmare, the C128 can run the 8502 at 2mhz so you didn't lose anything. Ideally they should have made an 80 column VIC. It would need to fetch multiple bytes per clock so that the CPU didn't get starved of bus activity. But at least then you could run faster than 1mhz without turning off the screen.

A 6809 would have at least doubled the price. I like the 68000 but it's the only Motorola CPU that is really any good, if it hadn't been so good then commodore wouldn't have paid the premium.