5 ms·
Interesting that it had roughly the same number of transistors as the 286 but appeared three years later but on a larger node size (so bigger die).
by klelatti 4y ago
Interesting that it had roughly the same number of transistors as the 286 but appeared three years later but on a larger node size (so bigger die).
- chasil 4y agoThe VAX was a 32-bit CPU with an mmu, the 286 was not. UNIX variants on the 286 had severe limitations (64k max program size). VMS was built for a much bigger machine than a 286. The fab was also in-house. "It is DEC's first single-chip microprocessor implementation of the VAX ISA and DEC's first self-fabricated microprocessor... "The MicroVAX 78032 contains 125,000 transistors on an 8.7 by 8.6 mm (74.82 mm2) die that was fabricated in DEC's ZMOS process, a 3.0 µm NMOS logic process with two layers of aluminum interconnect."
- Koshkin 4y agoThe 286 was a curious little beast. It did have a sort of an MMU, and, according to Wikipedia, The CPU was designed for multi-user systems with multitasking applications…
- dfox 4y ago286 and for that matter even 386 has the segment-based memory protection mechanism that is somewhat reminiscent of Burroughs mainframes, GECOS and maybe AS/400. There are two giant issues with the idea: it does not work that well on 16b word system and it is totally incompatible with what most of existing code written in C expects. So with 386 Intel had combined that mechanism with traditional MMU and somewhat hack-ish method to turn all that of (reportedly because Microsoft wanted that for Windows/386)
- retrac 4y agoA few operating systems, mostly UNIX clones, did exist that specifically took advantage of 286 protected mode. The 286 has user and supervisor modes, and could address up to 16 MB of physical memory. In protected mode it still used 8086 style segmented addressing, but the segments were virtual.
- Eleison23 4y agoThe bittersweet fact is that when the 80386 came out, OS designers dispensed with segmentation altogether, because it was conceptually so much easier to just flatten out a single vast address space. So despite the fact that i386 was now capable of really useful and intricate segmented memory architecture, it was the unsegmented, flat virtual address space that won the race.
- klelatti 4y agoYes my first reaction was that the VAX would have been a much better architecture but Intel's manufacturing lead meant that it could churn out 286s (and of course 386s in 1985) at much lower cost. Interesting to compare them both with the ARM1 which was 32 bit (no MMU) but only used 25k transistors on a 3 µm process - and which was more powerful than VAX 11/780. So both powerful and cheap to make.
- chasil 4y agoI really don't understand why Acorn wasn't purchased outright as soon as the samples were back from the fab. I think DEC was the first third-party implementation with StrongARM. https://en.m.wikipedia.org/wiki/StrongARM https://en.m.wikipedia.org/wiki/StrongARM
- klelatti 4y agoYes I think you're right on StrongARM which was the most powerful ARM CPU for a long time. Eventually made its way to Intel I think. I think everyone eventually had their own RISC - IBM, HP, AMD, Intel (i960) plus MIPs and SPARC of course and a few others. Arm eventually got traction because of the business model and because they intentionally didn't go head to head with the Intel x86 juggernaut. It wasn't obvious for a long time that their model would work though.
- KerrAvon 4y agoIIRC, StrongARM was the basis for XScale, which Intel foolishly spun off. They could have had a good chunk of the smartphone market, or at least a viable path into it.