On 2/9/20 2:02 PM, Adam Michlin via vcf-midatlantic wrote:
Ooo.. how could I forget Fairchild? Thanks! The AMD bit slice is new to me. Am I understanding correctly that it is not a discrete CPU but rather parts of a CPU that could be used together? Probably not a candidate for this exhibit, but I'm already having ideas for the next one!
Bit-slice is great stuff. There are many bit-slice chips, but the Am2901 essentially owned the market. It is a four-bit unit. Basically it's a processor building block used to construct a micromachine. You stack them up to whatever bit width you want, and program them with microcode to implement whatever macro-architecture you want. There are companion chips, like the Am2910 sequencer, etc. These are not required but come in handy. The sequencer can implement constructs like a microprogram counter, branches and jumps, etc. A few examples you've heard of: The VAX-11/730 uses a row of eight Am2901s to implement a 32-bit VAX processor, and the DECsystem-2020 uses a row of nine to implement a 36-bit PDP-10 processor. Both use RAM-based control stores, so when they power up they don't speak the VAX/PDP-10 instruction sets until after the microcode is loaded. This is generally the smallest/cheapest approach to build a large processor. The VAX-11/730 and DECsystem-2020 are very small, very low-end members of their respective families. But the bit-slice chips themselves are quite fast for their day, being big hot-running 1970s bipolar chips. It's also possible to use Am2901s (or other bit-slice chips) as processors in their own right. For example, many, many third-party disk controllers for DEC machines use a pair or a quad of Am2901s to implement their functionality. In this application they typically aren't running microcode, but are used as more of a microcontroller with firmware. The distinction is largely semantic, though, of course. It's great stuff. If you want to learn more about how all of this works, I recommend picking up a copy of "Bit-Slice Microprocessor Design" by John Mick and James Brick. This book is/was known in the industry as "Mick & Brick".
I'd love to find a Zilog Z8000, but don't imagine period correct Z8000s are so easy to come by. We have a Z8000 machine in the warehouse, but one of the big rules for this product is that no vintage computers will be harmed to make it happen.
Are you talking about just a Z8000 chip? I can provide that for the exhibit. It will need ESD protection, of course. -Dave -- Dave McGuire, AK4HZ New Kensington, PA