Hacker News Reader

Comment by nielsbot | Hacker News Reader

> “A microcomputer is a computer whose processor is a microchip: a single integrated circuit containing the whole processor.”

Small thing, but to have that finally explained after all these years… I never knew the explicit difference between a minicomputer and microcomputer for some reason.

View on HN

It was a bit more than that. At the time, chip technology wasn't at today's level; you couldn't put a 32-bit (or, originally, even 16-bit) system on a single chip. So micros were much less capable than minis. A mainframe was a computer that could run a company, with both the price and the performance to match. A mini wasn't that costly or that powerful, but it could run a department. A micro wasn't powerful enough to even do that, but it was much less expensive.

So, yes, it was "single chip CPU", but that correlated with a bunch of other things...

Yeah - and when the first single-chip CPUs were made, they were extremely cut-down. Forget about TLBs and operating modes - the intel 4004 didn’t even have hardware interrupts! They had to dispense with any kind of interrupt-driven IO and instead had to poll hardware.

It was a big challenge getting an entire CPU on a single chip back then. Arguably, every single microprocessor from the 4004 to the 386 was just restoring features that the minicomputers originally had.

Yeah, it wasn't that clear cut. After all, earlier micro CPUs like the 8088 had optional external floating point units. In general, memory management was integrated with the CPU early on in micros whereas it was a separate chip in mid-80s mini designs I'm familiar with. I/O was pretty separated out in both cases at that time as well.

The distinction is probably more around Andy Grove's horizontal stack of "commodity" microprocessors, OSs, etc. vs. the vertical stack of the micros where one company mostly made everything.

> In general, memory management was integrated with the CPU early on in micros whereas it was a separate chip in mid-80s mini designs I'm familiar with.

Memory management didn't make it into micros until the 386 generation. (At least on-chip memory management didn't.) In terms of this discussion, that's pretty late.

I’ll disagree because the 286 systems have quite a capable MMU - capable of running demand paged 286 System V Unix. Not that 64K segments were ultimately that useful as systems grew. But a better MMU than any PDP-11 for sure.

But as a separate chip, right? It wasn't on the same die as the 286, was it?

My understanding is the 286 had a limited MMU on board, with memory protection based on 64K segments. Some other CPUs, like the Motorola 68020, did require separate MMUs.

Yes, the 68020 had a separate MMU; the 68030 had it on-chip.

It was on the same die. Just segmented though, not paged (I was incorrect), though it did run protected Unix and Xenix quite well.

Reply on news.ycombinator.com