IBM PC with Zilog Z80A, realistic ?

[Michel Van]

About history of first IBM PC, their different versions:
That IBM wanted Intel 8086 since work with, and cheaper Zilog was own by potential competitor.
Other tell that IBM gave software company free hand to take the CPU, were Microsoft took the 8086.
But Original had Digital Research Inc. todo the Software for IBM5100 with CP/M (with Z80A ?)

Now the Zilog 80A is a software-compatible extension and enhancement of the Intel 8080
And Intel 8086 is internal 16-bit microprocessor, compatible extension of the Intel 8080 .

However is cheaper Z80A option for IBM PC ?
Either unter CP/M or modifed MS-Dos
And how look on long Term, if IBM goes for 16-bit PC?

 

[Dathi THorfinnsson]

No way was the IBM PC ever going to be an 8bit machine using an 8080 or Z80.

The 5100, introduced in 1975, was based on IBM's own PALM processor

IBM PALM processor - Wikipedia

en.m.wikipedia.org

a circuit board filled with lots of discrete logic, not a chip. And it was already partially 16bit.

As I understand it, the available chips looked at were the 8086, the ultimate choice, and Motorola's 68000.
At the time, I thought they picked the wrong one - the 8086 had the infamous 1MB memory limit ( 640K when graphics, ROM and IO spaces allocated). The 68000 had FAR more room for growth.
However, I was told that the 8086 had a drop-in 8087 math coprocessor, while the Motorola equivalent (68887???) required additional glue logic which would have made the computer too expensive.

But, no, no way are they going with an 8 bit processor.

 

[Michel Van]

The 5100, introduced in 1975, was based on IBM's own PALM processor

my mistake PC is IBM5150.

As I understand it, the available chips looked at were the 8086, the ultimate choice, and Motorola's 68000.

So far i know wanted IBM the Motorola 68000, but was not production-ready, as IBM design the PC,
That would match the story, IBM took the Intel 8086 because they had experience with 8080 microarchitecture.
Also why IBM cpu were rejected, due to the design constraint to use off-the-shelf parts.

 

[Anarch King of Dipsodes]

So far i know wanted IBM the Motorola 68000, but was not production-ready, as IBM design the PC,

My understanding is that IBM wanted the Motorola 6809. (the enhanced version of its 8-bit 6800). But they wanted Moto to commit to very large deliveries as a requirement. Moto wanted to reserve production capacity for the upcoming 68000, and declined the commitment. Intel said "Whatever you want, iBM sir!" So IBM went with the Intel 8088 (the 8-bit data bus version of the 8086).

NOTE: while the 6809 had only a 16-bit address space (64KB), it was quite possible to give it more storage with memory mapping. My employer at the time built 6809-based systems with 1M of memory.

 

[Nivek]

My understanding is that IBM wanted the Motorola 6809. (the enhanced version of its 8-bit 6800). But they wanted Moto to commit to very large deliveries as a requirement. Moto wanted to reserve production capacity for the upcoming 68000, and declined the commitment. Intel said "Whatever you want, iBM sir!" So IBM went with the Intel 8088 (the 8-bit data bus version of the 8086).

NOTE: while the 6809 had only a 16-bit address space (64KB), it was quite possible to give it more storage with memory mapping. My employer at the time built 6809-based systems with 1M of memory.

Interesting how would have IBM, Intel and Motorola changed if Moto pushed the 68K to IBM?

 

[Michel Van]

Interesting how would have IBM, Intel and Motorola changed if Moto pushed the 68K to IBM?

Issue was Timing
The Motorola 68K was not ready for mass production, as IBM finalise the PC hardware architecture.

My understanding is that IBM wanted the Motorola 6809.

That's new new to me, most sources say 68K or have they mistook 6800 with 68000 ?

It would have been fascinate senario had IBM took Motorola 6809 for PC and for AT goes Motorola 68000, until Power PC.

 

[Nivek]

Issue was Timing
The Motorola 68K was not ready for mass production, as IBM finalise the PC hardware architecture.

I see