Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Intel 80386, a Revolutionary CPU

xtof.info

Post reply on HN
Print view View original

71–80 of 180 posts

Re: Intel 80386, a Revolutionary CPU

#71

Post by zozbot234 »

johnklos wrote: post #44

I think the 80386's final design benefitted tremendously from the Motorola 68000, then the m68020. Had Motorola not released a proper 32 bit CPU without compromises, it could be argued that Intel would've had yet another stop-gap after the 80286, which itself wasn't intended to be a proper successor to the 8086/8088. As it is, the 80386 came with a number of compromises. For instance, there was no cache at all beyond…

> There were no atomic instructions (/LOCK wasn't useful for this), which is why many modern OSes support the 80486 but not the 80386.

Does the lack of atomics really matter, given that there was (AIUI) no SMP on the 386? You can always disable interrupts to make your operation 'atomic' in a uniprocessor context.

Re: Intel 80386, a Revolutionary CPU

#72

Post by ngcc_hk »

scrlk wrote: post #12
kristopolous wrote: post #4

They were in big trouble then. The entire company was riding on it being great. It could have easily gone awry as it did for Data General, Honeywell, CDC, AST, Tandy, Olivetti, Xerox, DEC Rainbow, AT&T Hobbit, Wang 2200 and Unisys. Strong survivorship bias on this one. Most of the once Titans are in or near the dustbin now, such as SDS, SDC and Fairchild. Intel's history was primarily as a memory manufacturer. They'r…

Andy Grove moving Intel from memory to microprocessors was an excellent strategic move. > "Business success contains the seeds of its own destruction. Success breeds complacency. Complacency breeds failure. Only the paranoid survive." Something that Intel's leaders didn't pay attention to during the 2010s.

There is even a story plus a term for it.

The story is about what if we all go out off this room and come back like a new guy. What would we do?

"strategic inflection point" ...

They decide to move from a memory company to a CPU company.

No access to Nikon but being just a Leica len maker for Canon (and famously found by DDD and used in Korea War), then move to nikon rangefinder (but strangely follow Zeiss approach more). Then jump ship to SLR by inventing Nikon F (and used in Vietnam War). It is just crazy move, but at least it is related. And "survive" and move on.

Or just like Fujifilm move to cosmetic in one stage as making film has some knowledge that can be re-used there. And survive and move on.

Re: Intel 80386, a Revolutionary CPU

#73

Post by Aloha »

WalterBright wrote: post #64
nxobject wrote: post #57

Earlier quoted context omitted.

Hmm – the smallest, most highly-integrated PDP-11 (-compatible) package ever made was the QFP 1806VM2, with around ~135k transistors; it integrated MMU, UART, parallel interface, keyboard controller, etc, but did floating-point instructions in interpretive microcode. I think that same transistor count was reached by Motorola on the 68020, which would've been around 1984, but would have needed the peripheral controlle…

The FPU for the 8086 was a separate chip, and the IBM PC still required a board full of chips to make a working computer. (If I recall correctly, it wasn't until the 486 that the FPU was incorporated.)

The IBM PC had an advantage in that most of the support parts were IIRC largely jellybean 74 series logic - could a PC-PDP have used similar COTS parts?

The larger issue with DEC was a strong NIH trend (almost as strong as IBM), I dont know if they could have bucked that trend to successfully launch a market winning PC. It probably would have looked like the DEC Professional, which I think looks like market failure.

So the dreams of a 64 bit extension to the PDP-11 might be stillborn ;-)

Re: Intel 80386, a Revolutionary CPU

#75

Post by Aloha »

nxobject wrote: post #57
Aloha wrote: post #53

Earlier quoted context omitted.

Thats an interesting alternative history thought experiment. I wonder how early one could capture the complexity of the full PDP-11 microarchitecture on a single chip? Would it have been affordable? What about the support hardware?

Hmm – the smallest, most highly-integrated PDP-11 (-compatible) package ever made was the QFP 1806VM2, with around ~135k transistors; it integrated MMU, UART, parallel interface, keyboard controller, etc, but did floating-point instructions in interpretive microcode. I think that same transistor count was reached by Motorola on the 68020, which would've been around 1984, but would have needed the peripheral controlle…

I think DEC's strong trend line of NIH (almost as strong as IBM) almost certainly dooms a PC-PDP - IBM only made the PC by effectively creating a skunkworks within the company that was focused solely on 'go to market' compared to the normal IBM development process. I dont know if DEC could or would have done that.

Re: Intel 80386, a Revolutionary CPU

#76

Post by dboreham »

WalterBright wrote: post #34
kristopolous wrote: post #4

They were in big trouble then. The entire company was riding on it being great. It could have easily gone awry as it did for Data General, Honeywell, CDC, AST, Tandy, Olivetti, Xerox, DEC Rainbow, AT&T Hobbit, Wang 2200 and Unisys. Strong survivorship bias on this one. Most of the once Titans are in or near the dustbin now, such as SDS, SDC and Fairchild. Intel's history was primarily as a memory manufacturer. They'r…

The DEC Rainbow would have been fine if they didn't do things like require special floppy disks that cost $5 each. DEC should have packaged the LSI-11 into a consumer machine. They had all the software, which was top shelf. I had an H-11, it was a great machine.

I'm a big pdp-11 fan but this wouldn't have worked because 128K address space isn't enough even in 1975. Listen to Dave Cutler talk about this in the 3h long interview.

Re: Intel 80386, a Revolutionary CPU

#77

Post by dboreham »

nxobject wrote: post #57
Aloha wrote: post #53

Earlier quoted context omitted.

Thats an interesting alternative history thought experiment. I wonder how early one could capture the complexity of the full PDP-11 microarchitecture on a single chip? Would it have been affordable? What about the support hardware?

Hmm – the smallest, most highly-integrated PDP-11 (-compatible) package ever made was the QFP 1806VM2, with around ~135k transistors; it integrated MMU, UART, parallel interface, keyboard controller, etc, but did floating-point instructions in interpretive microcode. I think that same transistor count was reached by Motorola on the 68020, which would've been around 1984, but would have needed the peripheral controlle…

68020 is much more complex than any pdp-11.

Re: Intel 80386, a Revolutionary CPU

#78

Post by WalterBright »

Aloha wrote: post #75
nxobject wrote: post #57

Earlier quoted context omitted.

Hmm – the smallest, most highly-integrated PDP-11 (-compatible) package ever made was the QFP 1806VM2, with around ~135k transistors; it integrated MMU, UART, parallel interface, keyboard controller, etc, but did floating-point instructions in interpretive microcode. I think that same transistor count was reached by Motorola on the 68020, which would've been around 1984, but would have needed the peripheral controlle…

I think DEC's strong trend line of NIH (almost as strong as IBM) almost certainly dooms a PC-PDP - IBM only made the PC by effectively creating a skunkworks within the company that was focused solely on 'go to market' compared to the normal IBM development process. I dont know if DEC could or would have done that.

I was a DEC-head in the 70's and 80's, and along with my fellow DEC-heads anxiously awaited DEC's entry into the PC arena. Everyone was excited to see the rollout of the Rainbow, sure it would be a killer machine like other DEC machines. After the presentation, we were all in shock. It did not play to any of DEC's strengths, and was just a crummy, proprietary x86 insult.

That was the end of our love affair with DEC. Very sad.

Re: Intel 80386, a Revolutionary CPU

#79

Post by Gibbon1 »

Aloha wrote: post #73
WalterBright wrote: post #64

Earlier quoted context omitted.

The FPU for the 8086 was a separate chip, and the IBM PC still required a board full of chips to make a working computer. (If I recall correctly, it wasn't until the 486 that the FPU was incorporated.)

The IBM PC had an advantage in that most of the support parts were IIRC largely jellybean 74 series logic - could a PC-PDP have used similar COTS parts? The larger issue with DEC was a strong NIH trend (almost as strong as IBM), I dont know if they could have bucked that trend to successfully launch a market winning PC. It probably would have looked like the DEC Professional, which I think looks like market failure.…

I read an essay by a guy that worked on project to produce a DEC minicomputer using ECL logic. And there was yet another group working on the DEC Alpha. At the time the main group was using most of the companies resources betting the company on dethroning IBM in the main frame arena. And was trying to stab the Alpha and Minicomputer group in the back.

So probably not.

Suspect IBM's skunk work project was done as a hedge and anti-trust reasons. Personal Computers were going to take some business away from them they wanted it to be their product not someone else. Anti-trust also meant it needed to use off the shelf stuff.

Re: Intel 80386, a Revolutionary CPU

#80

Post by bonzini »

StillBored wrote: post #66

I really wish people would stop applying the "flat 32-bit" revisionist history to the 386. That wasn't its obvious target, but rather picking up the important "capability" arch features which were seen as the future before unix/c/risc/single supervisor/ideas destroyed the previous 30 years of mainframe/minicomputer OS research in things like security. So, what this article fails to really clarify is that the segment…

> Pointers (capabilities, aka selectors) can have not only a base address, but a hardware enforced limit

There are only 8k possible pointers in the LDT, plus 8k in the GDT. The x86 segmented model isn't really suitable for implementing capabilities.

Post reply on HN