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Steve Wozniak was incredibly foresighted when designing the Apple II, to make sure that expansion cards could disable the default ROMs and even disable the CPU, making this kind of thing possible. The article mentions a chunk of memory "used by peripheral devices"; every expansion card got its own slice of the address space, so you could plug a card in any slot and it would Just Work (maybe you'd have to tell software what slot the card was in). I was very disappointed when I "upgraded" to a 386 and suddenly cards had to be manually configured to non-conflicting IRQs and I/O addresses.

I bought an Apple II and then a SoftCard. I was trying to learn 'C' and there was a compiler on CPM (Borland) but not on the Apple II.

It is always hard to go back and understand what it was like before an event. Like the Velvet Revolution. But at the time I was working on an IBM 360, mostly doing Fortran for scientists running anemometer simulations. The center for this activity was the person in charge of the 360 who could dole out time on the computer.

The power dynamic was something I did not really notice, but in retrospect this was frustrating for the mathematicians/scientist trying to run simulations. They had to queue up and wait.

Then one day a mathematician brought in an Apple II running VisiCalc. His own personal computer. He ran his simulations on that.

It was like our small world trembled as the tectonic plates of technology shifted. The power shifted just in that one instant. It was cool - how we saw the world changed in one instant.

Years later. the Apple Dos Compstibility Card (code named Houdini) could do the same thing. It had a 486DX/2-66 and a Sound blaster card on board. By default it shared the host Mac’s memory and you could run both simultaneously. But it wasn’t a great experience on either side. They both ran slower

Alternatively, you could put up to a 32MB RAM SIMM directly on the card.

Now that I think about it, my first Mac did the same thing with the Apple //e card.

Cool post from Raymond as usual!

I’d like to add that the hardware for the SoftCard was designed by Tim Paterson at SCP about the same time he was writing the future MS-DOS

I remember my dad using the Z80 Softcard to run WordStar, which was astonishingly powerful considering how long ago it was king of word processors. I’d be surprised if some of the control keys hadn’t influenced our editors, although as a Vim user I can’t immediately think of any.

From Google

Manufacturing and development process: Although Microsoft developed the idea, the actual engineering and prototyping were done by Tim Paterson at Seattle Computer Products (SCP). Don Burtis of Burtronix redesigned the card, and California Computer Systems manufactured it for Microsoft

I wonder if anyone ever used the Z80 Softcard or one of its many clones to run something different than CP/M?

It was so much easier to do hardware shenanigans with these old-school chips where the pins on these breadboardable chips actually corresponded to memory address bits.

Sounds like the 6502 could have been doing more at the same time as the z80 for a sufficiently careful program.

This is great, I’m building new machines on the 6502 and can use this. Thanks.

Ooh, the Z80 refresh line. You can have a program that writes to the R register in a loop and prevent the refreshes from happening.

One of the biggest disappointments of the 8-bit era was the Commodore 128 not being able to use both the 8502 and Z80 CPUs in some kind of coprocessor setup.

"According to Wikipedia..." aargh Wikipedia is not the source!

Would be cool if Microsoft would focus on engineering instead of blog posts