reminds me of the days computers had a "turbo" button and a LCD read out of the clock speed on the case. "66Mhz" => "90" ... now we're cooking
Examining the silicon dies of the Intel 386 processor
11–20 of 64 posts
Re: Examining the silicon dies of the Intel 386 processor
#12One of my greatest treasures as a young computer nerd was a bare 386(I think) chip that I received after sending away for it via an Intel ad I found in Byte magazine. I just had to cut out part of the page and mail it in. Several months later I get a package back with the naked processor glued to stiff card along with a low powered magnifying glass to scope it out with.
I really wish I still had that thing.
Re: Examining the silicon dies of the Intel 386 processor
#13Author here. I've been looking at the 386 if anyone has questions. This post was inspired by userbinator's discussion on HN a couple of weeks ago about how many transistors there are in the 386.
Love the post! Some DOI and Bitsavers links are broken (linking to righto.com or 404s). Also, where can I find "Automatic Place and Route Used on the 80386"? DDG only contains one result: this post.
There was some discussion of the automatic placement in this panel interview.
If I remember correctly, the software that performed the placement was written by a graduate student who debugged it from a terminal at his dormitory. It was one of many project decisions on the i386 that management would have absolutely stopped had they been made aware.
https://www.computerhistory.org/collections/catalog/10270201...
"386 is a complicated processor (by 1980s standards), with 285,000 transistors..."
Interesting that ARM1 was only 25,000 transistors. Did the i386 really have additional features that justify an order of magnitude?
One thing is certain in retrospect: Intel should have bought Acorn, not Olivetti.
Edit: Wow, there is even more detail on the placement software in the Righto article; the software was "Timberwolf" written by Dr. Carl Sechen.
Edit2: It appears that later versions of Timberwolf were sucked into Yale's licensing.
...Sechen served as an expert witness in the Cadence/Avanti trial in 2000 and 2001... "I had a chance to examine a great deal of the code in question when I was an expert witness on the trial. It was amazing – I even saw my own TimberWolf code in their tool, where only a single line of code had been changed. And I don’t mean the earlier, far-inferior version of TimberWolf available from Berkeley. The version I found in Avanti’s suite was a far more state-of-the-art version that had somehow been ‘acquired’ from Yale."
http://www.aycinena.com/index2/index3/archive/uw%20-%20seche...
Edit3: Graywolf is a fork of the last free version of Yale's Timberwolf.
Re: Examining the silicon dies of the Intel 386 processor
#14Author here. I've been looking at the 386 if anyone has questions. This post was inspired by userbinator's discussion on HN a couple of weeks ago about how many transistors there are in the 386.
Love the post! Some DOI and Bitsavers links are broken (linking to righto.com or 404s). Also, where can I find "Automatic Place and Route Used on the 80386"? DDG only contains one result: this post.
Thanks! I've fixed the links, so let me know if you see any other broken ones.
The "Automatic Place and Route Used on the 80386" article is from Intel Technology Journal, Spring 1986, p29-34. I don't think you can find it anywhere; Pat Gelsinger sent me a copy. Email me (ken.shirriff@gmail.com) and I'll send it to you.
Re: Examining the silicon dies of the Intel 386 processor
#15Could the “C” in 80C386I stand for CMOS? Wasn’t that pattern used for the 80C88, for example?
All Intel 386s were CMOS though, so the added C on the die-shrink shouldn't mean CMOS.
Re: Examining the silicon dies of the Intel 386 processor
#16Author here. I've been looking at the 386 if anyone has questions. This post was inspired by userbinator's discussion on HN a couple of weeks ago about how many transistors there are in the 386.
Total amateur here: does a 386 have “cleverness” or optimizations or does it just quite literally chug through a stream of instructions, adjusting registers and memory? I guess by this I am thinking about how newer processors do all kinds of stuff at the microcode level that mean you cannot anticipate precisely what instructions are being executed in what order.
Well, yes and no. The 386 is chugging through the stream of instructions sequentially, unlike modern processors. There are various clever optimizations, though. First, there is some pipelining, so the microcode for the next instruction can execute while the previous one is finishing. Second, the CPU has 16 bytes of prefetching, so instructions are fetched from memory asynchronously from their execution. So you know what instructions are executed and in what order, but the timing is fairly unpredictable.
I should mention that microcode in the 386 is pretty different from micro-ops that modern processors run. They both break machine instructions down into smaller steps. But microcode runs sequentially, while micro-ops are sort of tossed into the CPU and run independently through a dataflow engine, with everything sorted out at the end to look sequential. Confusingly, modern processors use "microcode" to hold the micro-ops for complicated instructions that can't be handled by the regular instruction decoder; this is sort of like old-style microcode, but not exactly.
Re: Examining the silicon dies of the Intel 386 processor
#17Author here. I've been looking at the 386 if anyone has questions. This post was inspired by userbinator's discussion on HN a couple of weeks ago about how many transistors there are in the 386.
About what rough area percentage (or some other metric if you think there's a clearer comparison) of a 386DX is standard cells versus hand layout?
Looking at the die, I'd say roughly 1/3 of the die is standard cell. I think some of it was standard cell but with hand layout, rather than automatic place and route. About 1/4 is the datapath, which is highly optimized. Maybe 10% is the microcode ROM.
Re: Examining the silicon dies of the Intel 386 processor
#18Author here. I've been looking at the 386 if anyone has questions. This post was inspired by userbinator's discussion on HN a couple of weeks ago about how many transistors there are in the 386.
Great post! Any idea how the turbo button worked? It seems like, given the transistor difference between the 8086 and 386, that merely decreasing the clock frequency wouldn't be enough?
Re: Examining the silicon dies of the Intel 386 processor
#19Earlier quoted context omitted.
Love the post! Some DOI and Bitsavers links are broken (linking to righto.com or 404s). Also, where can I find "Automatic Place and Route Used on the 80386"? DDG only contains one result: this post.
Thanks! I've fixed the links, so let me know if you see any other broken ones. The "Automatic Place and Route Used on the 80386" article is from Intel Technology Journal, Spring 1986, p29-34. I don't think you can find it anywhere; Pat Gelsinger sent me a copy. Email me (ken.shirriff@gmail.com) and I'll send it to you.
You can always upload it to Archive.org if you feel so inclined
Re: Examining the silicon dies of the Intel 386 processor
#20Today I learned that the "s" in SX means "single" and "d" in DX means double. The DX has double the data bus width of the SX (32-bit vs 16-bit).