The Bellmac-32 was pretty amazing for its time - yet I note that the article fails to mention the immense debt that it owes to the VAX-11/780 architecture, which preceded it by three years.
The VAX was a 32-bit CPU with a two stage pipeline which introduced modern demand paged virtual memory. It was also the dominant platform for C and Unix by the time the Bellmac-32 was released.
The Bellmac-32 was a 32-bit CPU with a two stage pipeline and demand paged virtual memory very like the VAX's, which ran C and Unix. It's no mystery where it was getting a lot of its inspiration. I think the article makes it sound like these features were more original than they were.
Where the Bellmac-32 was impressive is in their success in implementing the latest features in CMOS, when the VAX was languishing in the supermini world of discrete logic. Ultimately the Bellmax-32 was a step in the right direction, and the VAX line ended up adopting LSI too slowly and became obsolete.
I read through its instruction set manual, and found an instruction with unusual behaviour: Its 'ASL` (arithmetic shift left) instruction.
It shifts all bits except for the sign bit, leaving it unchanged.
I have read many ISA's manuals and not seen this elsewhere.
Most ISAs don't have separate arithmetic and logic left shift instructions.
On M68K, which does, the difference between `ASL` and `LSL' is only that the former sets the Overflow flag if any of the bits shifted out is different from the resulting sign bit whereas the latter clears it.
The article handwaves over why the chip wasn't a success, which makes my first thought of "how much did each chip cost" all the more relevant. This is such an uplifting story until you think about how the 8086 is just about to wipe it off of the map.
Bellmac-32 went 32-bit CMOS when everyone else was still twiddling 8-bit NMOS, then got shelved before the afterparty. IEEE giving it a milestone in 2025 is basically a lifetime achievement trophy for the domino-logic DNA inside every phone SoC today late, but deserved
> With no CAD tools available for full-chip verification ... the team resorted to printing oversize Calcomp plots. The schematics showed how the transistors, circuit lines, and interconnects should be arranged inside the chip to provide the desired outputs. The team assembled them on the floor with adhesive tape to create a massive square map more than 6 meters on a side. Kang and his colleagues traced every circuit by hand with colored pencils, searching for breaks, overlaps, or mishandled interconnects.
This is the main thing I wanted to know, the last section heading in the article, and not explained by the remaining text. AT&T choosing someone different is a lame excuse (others could have bought in, like how Apple got ideas from Xerox PARC), and the rest is padded out with a restatement of how the Bellmac-32's ideas shaped future chip development.
If you were a CS student at UIUC in the late 80s your sophomore weed-out class in C and assembly language coding was on this processor. It was a lot more fun to write for this core compared to Intel.
And it was the only processor I ever used that had a STRCPY opcode.
> “Ma Bell” had dominated American voice communications, with its Western Electric subsidiary manufacturing nearly every telephone found in U.S. homes and offices.
When others do it, they call it communism. When they do it themselves, they call it good business.
32 bits that changed microprocessor design
(spectrum.ieee.org)136 points by mdp2021 22 May 2025 | 53 comments
Comments
The VAX was a 32-bit CPU with a two stage pipeline which introduced modern demand paged virtual memory. It was also the dominant platform for C and Unix by the time the Bellmac-32 was released.
The Bellmac-32 was a 32-bit CPU with a two stage pipeline and demand paged virtual memory very like the VAX's, which ran C and Unix. It's no mystery where it was getting a lot of its inspiration. I think the article makes it sound like these features were more original than they were.
Where the Bellmac-32 was impressive is in their success in implementing the latest features in CMOS, when the VAX was languishing in the supermini world of discrete logic. Ultimately the Bellmax-32 was a step in the right direction, and the VAX line ended up adopting LSI too slowly and became obsolete.
We really could use a place like that today.
It shifts all bits except for the sign bit, leaving it unchanged.
I have read many ISA's manuals and not seen this elsewhere. Most ISAs don't have separate arithmetic and logic left shift instructions. On M68K, which does, the difference between `ASL` and `LSL' is only that the former sets the Overflow flag if any of the bits shifted out is different from the resulting sign bit whereas the latter clears it.
This is the main thing I wanted to know, the last section heading in the article, and not explained by the remaining text. AT&T choosing someone different is a lame excuse (others could have bought in, like how Apple got ideas from Xerox PARC), and the rest is padded out with a restatement of how the Bellmac-32's ideas shaped future chip development.
And it was the only processor I ever used that had a STRCPY opcode.
This is the real first, more significant than anything else. Hardware design catering to the C language started here.
When others do it, they call it communism. When they do it themselves, they call it good business.