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

[psxphill]

I've never heard that story from either Bil or Dave.

From On The Edge:

To fix the problem, Herd required the C128 to start at memory address zero, but the 8502 started elsewhere. "One night, everybody left and it was broken," says Herd. "During the night, I said, 'I have no way to fix this, unless we startup by not starting at that address.' I said, 'Hey, Von. The Z80 chip starts from zero, doesn't it?' He said, 'Yup.' I said, 'Cool. I need somebody wire wrapping tonight.'"
The hour was too late to purchase a Z80 chip, so Herd looked elsewhere. "Everybody had doorstops that were actually Sinclairs," he recalls. "I went and tore open my doorstop because we didn't own a Z80 chip in the place."


I don't believe they re-used the Z80's in production models though. After hearing about how the C64 was put into production for Christmas however, nothing would surprise me

Putting in an 8088 would likely have not helped much as making the computer MSDOS compatible to any real degree would have been impossible. An NEC V20 would have been better as it could run CPM in it's 8080 mode, but you can also run 8086 software. It lacks the extra Z80 instructions but most CPM software is compatible with 8080 anyway (Z80 is an 8080 clone with added instructions). It might not add much, but you also wouldn't really lose anything.

The C128 was like the A3000. Both were based on custom chips from a previous design, but with extra glue around them because there was no time/money/inclination to improve them. If the C128 had an 80 column VIC that could work when the CPU was running at 2mhz then it would have been a worthwhile upgrade & much closer to the C65 but still C64 compatible.

The C65 was designed during the time when AAA was in development hell, I can understand why in that environment the C65 project would have made some sort of sense and it probably would have sold if it was cheap enough. Another couple of engineers also went off and pushed through the Pandora project, which turned into AGA.

[Rob]

Thanks for quoting that.  I gave away my copy of On The Edge some time ago and didn't remember exactly what was written.

[psxphill]

Thanks for quoting that.  I gave away my copy of On The Edge some time ago and didn't remember exactly what was written.

I still have mine, but I forgot where it was written anyway. I only found it by googling:

c128 z80 doorstop

[motrucker]

The c128dcr had a built in 71, Both commodore and CMD made mice for the c64/128
Lt Kernel(SP?) and CMD made hard drives.

The z80 was chosen on purpose not for just cpm, but it was a necessary chip to make all 3 modes live together,iirc it used the z80 for its early startup.

This is the way I remember it too. Using an 8088 in the C-128 makes little to no sense at all.

[psxphill]

This is the way I remember it too. Using an 8088 in the C-128 makes little to no sense at all.

It might have made sense to design it in at the start, although an NEC V20 would make more sense as you could still run CPM on it. However you would want either want to increase the MMU address space or connect it on the other side of the MMU so you could address all the memory from 8088 mode using segments.

The magic voice startup problem was solved because the Z80 doesn't start by fetching the same address as the 6502, but neither does the 8088/V20. So it should have been an equally good workround, except I doubt anyone at commodore was using an 8088 computer as a doorstop at the time.

[RobertB]

From On The Edge:

To fix the problem, Herd required the C128 to start at memory address zero, but the 8502 started elsewhere. "One night, everybody left and it was broken," says Herd. "During the night, I said, 'I have no way to fix this, unless we startup by not starting at that address.' I said, 'Hey, Von. The Z80 chip starts from zero, doesn't it?' He said, 'Yup.' I said, 'Cool. I need somebody wire wrapping tonight.'"
The hour was too late to purchase a Z80 chip, so Herd looked elsewhere. "Everybody had doorstops that were actually Sinclairs," he recalls. "I went and tore open my doorstop because we didn't own a Z80 chip in the place."

Heh, I will reconfirm with Bil.  As Bil and Leonard Tramiel said at CommVEx, the Brian Bagnall book(s) is/are not entirely accurate.

Truly,
Robert Bernardo
Fresno Commodore User Group
http://www.dickestel.com/fcug.htm

[psxphill]

Heh, I will reconfirm with Bil.  As Bil and Leonard Tramiel said at CommVEx, the Brian Bagnall book(s) is/are not entirely accurate.

If you watch all of Bil's talks back to back you should detect some inconsistencies. It's no wonder the book is not accurate.

[jj]

The Amstrad CPC 6128 also shipped with CP/M.  I never used it much either than for disk work.   Think did have a spread sheet prog I used to use on it occasionally.  Always  preferred Amstrad BASIC

[Iggy]

CP/M 3.0 was only 2 years old when the 128 came out and there was a huge library of software available for it including business and productivity software that was seriously lacking on the C64.

All of it text based with no graphics or sound.
Still a step backwards.

[glitch]

Oh yes, I'm not trying to stir up any which OS is better argument - I was just thinking of what if the 8088 was used instead and what different path MAY have unfolded - had they perhaps made the C128 into some PC compatible too.

I remember seeing the DEC Rainbow and thinking it was cool as well.

[Iggy]

Oh yes, I'm not trying to stir up any which OS is better argument - I was just thinking of what if the 8088 was used instead and what different path MAY have unfolded - had they perhaps made the C128 into some PC compatible too.

I remember seeing the DEC Rainbow and thinking it was cool as well.

Glad to meet someone else that remembers that system.
It was pretty cool, but really expensive for a PC clone.
Also had the first AND processor I had ever seen inside.

[psxphill]

I was just thinking of what if the 8088 was used instead and what different path MAY have unfolded - had they perhaps made the C128 into some PC compatible too.

It would have been impossible to make it PC compatible. Using the 8088 would also not have solved the issue why the Z80 was put in there to start with. In most of Bil's videos he says it was because the CP/M cartridge exceeded the amp budget and the decision to start the Z80 first instead of the 6502, to fix magic voice autostart, came later.

Bil learnt what C64 compatibility meant when they built the C128. IBM learnt what PC compatibility meant when they built the IBM PCjr. A C128 with an 8088 would have been less compatible than the PCjr, which itself was a failure.

PC compatibility never helped the Amiga either.

CP/M was more suited because of hardware fragmentation, each manufacturer made hardware to their own design and so applications had to go through the OS. While there was some fragmentation in the MS-DOS market to start with (Chuck Peddles Victor/Sirrius for example) by 1985 the market demanded that every piece of CGA/DMA/floppy/hard disk/sound hitting software would work.

An NEC V20 on the other hand would have allowed CPM-80 and CPM-86 applications to run & we could even have seen a port of GEM rather than GEOS.

[Iggy]

It would have been impossible to make it PC compatible. Using the 8088 would also not have solved the issue why the Z80 was put in there to start with. In most of Bil's videos he says it was because the CP/M cartridge exceeded the amp budget and the decision to start the Z80 first instead of the 6502, to fix magic voice autostart, came later.

Bil learnt what C64 compatibility meant when they built the C128. IBM learnt what PC compatibility meant when they built the IBM PCjr. A C128 with an 8088 would have been less compatible than the PCjr, which itself was a failure.

PC compatibility never helped the Amiga either.

CP/M was more suited because of hardware fragmentation, each manufacturer made hardware to their own design and so applications had to go through the OS. While there was some fragmentation in the MS-DOS market to start with (Chuck Peddles Victor/Sirrius for example) by 1985 the market demanded that every piece of CGA/DMA/floppy/hard disk/sound hitting software would work.

An NEC V20 on the other hand would have allowed CPM-80 and CPM-86 applications to run & we could even have seen a port of GEM rather than GEOS.

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).
Of course a system could have been built with both PC and C64 compatibility.

And the PCjr's video modes lived on in the Tandy 1000 series.
So that machine did have some significance.

GEOS and GEM? Almost as ugly a solution as CP/M.
MS-DOS and Windows compatibility have far more utility.

Most of your post appears to be unsupported opinion, unless I am reading it wrong.

[Rabbi]

@Glitch:

A far better choice would've been an NEC V20 or NEC V30 chip, as it would've allowed MS-DOS in addition to CP/M, but you have to remember those chips probably cost significantly more than a Zilog Z80A at that time the C= C128 was introduced in January 1985 (according to Wikipedia).  C='s choice of a Z80A was a cheaper CPU chip then an 8088, V20, or a V30.  The C128 was already more expensive than the C= C64 computer.  Price was a big thing back then.  Also, don't forget that there was most likely licensing fees for MS-DOS, too, and that would've added to its final cost, as well as the C128 development team needing to get MS-DOS properly interfacing on the C128.  Hindsight is always 20/20.

On another note, why don't you install AmigaZ80 from AmiNet instead of testing CP/M on a TRS-80 Model 4P?  I uploaded that file to AmiNet.

[Iggy]

CBM did make the desktops, like the Commodore Colt, PC-10, PC-20, PC-30, (and more), and 286, 386, and 486 laptops.

Truly,
Robert Bernardo
Fresno Commodore User Group
http://www.dickestel.com/fcug.htm

So if you consider those projects, wouldn't a C64 expansion card have made sense?

[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).