I think there were actually 68000 transistor positions. In the ROMs and PLAs not every potential transistor is populated but the missing ones were counted as well. But the number of actual transistors is only slightly smaller so it doesn't really matter.
I do not remember the exact number of transistors in MC 68000, but I think that it was less than 40000, so not just slightly smaller. In any case, it had more than twice as many transistors as Zilog Z8000, which was super-optimized for size (a very bad decision of Zilog, which lead to a too long time-to-market and to many initial bugs), and slightly more than 4/3 times as many transistors as Intel 8086.
The 68000 transistors number claimed by the Motorola marketing was close to what you get by dividing the die area to the area of one transistor, so it did not correspond to actual transistor positions.
The MC68000 die had large areas occupied with microprogram ROMs, and there as you say only a part of the array of transistors are active, depending on the stored bits. Nonetheless, a significant part of the die was occupied with random logic, where all the physical transistors are used and a part of the area does not have any transistors.
One chip that could be used as a memory mapper for the 9900 (but wasn't in the TI99/4A) was the 74LS670, which was used in the IBM 5150 PC to allow the 8237 DMA chip to access more than 64KB (a limit that wasn't a problem when used in a 8080 system).
Note that RISC5 [1], a project created as a target for Wirth's Oberon compilers, is a different project from RISC-V [2], a project created at Berkeley which became what is currently the most popular open source ISA.
We were stuck with 33MHz PCBs for a long time as people kept trying and failing to get 50MHz PCBs to work. Then Intel came out with the 486DX2 which allowed you to run a 50MHz processor with an external 25MHz bus (so a 25MHz PCB) and we started moving forward again, though we did eventually get PCBs to go much faster as well.
The Transputers (mentioned in other comments) had already decoupled the core speed from the bus speed and Chuck Moore got a patent for doing this in his second Forth processor[1], which patent trolls later used to extract money from Intel and others (a little of which went to Chuck and allowed him to design a few more generations of Forth processors).
> We were stuck with 33MHz PCBs for a long time as people kept trying and failing to get 50MHz PCBs to work.
What is the current best symbol rates we get on PCB traces? I know we’ve been multiplexing a lot of channels using the same tricks we used with modems to get above 9600bps on POTS.
The naming of processor sizes is the subject of debate. I call a "pure 8 bit processor" one that has 8 bits for both data and addresses. Like the Kenbak-1. But these are so rare and educational rather than practical that it is very reasonable to call hybrid 8 bit / 16 bit processors just "8 bit".
This use of sloppy terms shouldn't make us forget that they are using an address extension trick, just like all those 16 bit processors that wanted to go beyond 64KB (for byte addressed such as the PDP-11, Z8000 or 8086) or 128KB (for word addressed, like the Xerox Alto's modified Data General Nova model).
Michael J. Flynn, best known in the computing world for his taxonomy of parallel computing (SISD, SIMD, MISD and MIMD), passed away on December 24, 2025
Most people are not aware that after the failure of the PS/2 attempt to control the PC market, IBM tried a third time using 7 patents it had for the PC AT (they didn't have any on the original PC or the XT). In the first half of the 1990s they went after the chipset makers (mostly in Japan at that time) and in the second half of the 1990s they went after the PC makers themselves all around the world. The would threaten to sue for all machines made up to that point unless they licensed not only the 7 AT patents (which would expire in 2001) but also a bunch of other unrelated patents that were much newer. As far as I know everybody signed the deal, which meant that IBM could make money without actually making any PCs themselves.
This is true, but the patents were all RAND-licensed, so the press reported that IBM made about $5 per PC. Which isn't nothing, but IBM had no ability to restrict PCs market segments (like they had with Microchannel). So we soon saw "commodity" PC servers and even midrange systems, stealing IBM's bread+butter.
reply