The Heathkit H11 was available either as a kit or pre-assembled. It never became really popular in the West, but it was one of the most powerful PCs available in 1978. It used the LSI-11 small format of the PDP-11, and came with 4 kwords of memory for $1295. (That is 8 kbytes, but DEC preferred to refer to memory as register size, which was 16 bits.) It could be expanded to 32 kwords. IIRC, the LSI-11 CPU could actually handle up to 128 kwords (using bank swapping and/or memory-tunnel registers), but any memory above 32 kwords would have to be off the motherboard.
I agree with Andrew that the PDP architecture was fascinating and conceptually easy to understand. I used and programmed one at work for many years.
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I apologize to Alex Hajnal and others for using my own terminology, "memory tunnel registers". I was getting tired and chose not to look up the details on something that had very little to do with the question. The PDP-11 family offers several ways to access memory beyond 64 kbytes. One is the traditional memory mapping sort of deal where pages of memory can be mapped into and out of the accessible 64 kbytes. I was not referring to that.
The Q-Bus (used by LSI-11) offered 18 bits of physical address space, spanning 256 kbytes total. (Although Ken Gober indicates that on Heath's H11, the upper 2 bits of addressing were not wired, which would limit that machine to just 64 kbytes. I'm speaking of a fully addressed machine now.) With a linear mapping, the full memory space could still be accessed via 2 bits of the Processor Status register (PS), which provided address bits 16 and 17. Four instructions existed to access the full memory space.
- MTPI -- move to previous instruction space
- MTPD -- move to previous data space
- MFPD -- move from previous data space
- MFPI -- move from previous instruction space
What these instructions would do is push or pop a 16-bit word, accessing full physical memory via R6, the stack pointer (SP).
I didn't remember all the details, just that you get access any memory location directly without using memory management. Since it was one word at a time, the phrase I came up with was "memory tunnel registers". I guess the terminology almost fits, because the action does use both the SP and 2 bits of the PS.
