kens

44 ms·

661.
by kens 3y ago
You're describing a "hybrid computer". These were introduced in the late 1950s, combining a digital processor with analog computing units. I don't understand why you and kragen want to redefine standard terms; this seems
662.
by kens 3y ago
The official name for the LVDC's logic is triple modular redundant (TMR). The voting mechanism simply picks the majority, so it can tolerate one failure. The LVDC is a serial computer, which makes voting simpler to implement, since you
663.
by kens 3y ago
It's always been an option to use shielding rather than rad-hard chips or in combination. RCA's SCP-234 aerospace computer weighed 7.9 pounds, plus 3 pounds of lead sheets to protect the RAM and ROM. The Galileo probe used sheets
664.
by kens 3y ago
The Apollo Guidance Computer was the best technology when it was designed, but it was pretty much obsolete by the time of the Moon landing in 1969. Even by 1967, IBM's 4 Pi aerospace computer was roughly twice as fast and half the size
665.
by kens 3y ago
> Apollo 11 spacecraft contains 4 computers Analog computers don't get the respect they deserve. There's one more computer, the FCC. The Flight Control Computer is an analog computer in the Saturn V that controlled the rocket
666.
by kens 3y ago
This is a very interesting article on computer history. There's a lot that I disagree with, though...
667.
by kens 3y ago
The HP Journal article mentions the 9% yield as if they are perfectly fine with it. They were building these chips internally for high-margin gear (as you said), so it probably didn't matter if the chip cost $10 or $100, as long as it
668.
by kens 3y ago
I don't have figures for modern yields. I hope the yield is better. But I think there are fundamental difficulties with matching up the sapphire and silicon crystals that tends to produce faults.
669.
by kens 3y ago
Well, John McMaster was able to do some IR imaging of a chip: https://hackaday.com/2019/06/20/seeing-transistors-switch-in... But in this case, I think it's easier to squint at the die to distinguish the
670.
by kens 3y ago
We didn't see anything obviously wrong with the part. One bit of communication with the microprocessor was flaky, so it was probably a weak transistor. The consequence was that the Z80 attempted to look up a command in a lookup table,
671.
by kens 3y ago
Peregrine Semiconductor makes various SOS products. Here's a random example, an RF digital attenuator: https://www.psemi.com/pdf/datasheets/pe43205ds.pdf
672.
by kens 3y ago
Author here if anyone has questions. A bit of a change from my usual x86 chips...
673.
by kens 3y ago
The 386 has two layers of metal, which makes it an order of magnitude more difficult to reverse engineer. I don't have a good process for removing one layer of metal at a time, so I end up having to puzzle over faint patterns in the me
674.
by kens 3y ago
I was thinking of writing about the self-test circuitry. It doesn't expose things in a JTAG-like way, which came later. The main self-test is that if you boot the chip with the BUSY pin set, it goes through a self-test of all the PLA a
675.
by kens 3y ago
I'd recommend my blog post rather than a Twitter thread: https://www.righto.com/2023/12/386-xor-circuits.html
676.
by kens 3y ago
It sounds like you did some very interesting experimentation with the prefetch queue. Realistically, I'm unlikely to investigate the 386 prefetch queue to that level of detail, but if I do, your tests would be useful.
677.
by kens 3y ago
I've looked at a few higher-power chips, such as the venerable 7805 voltage regulator, but I don't know if that's high-power enough for you :-) There's no high-power secret inside that chip except it uses large transisto
678.
by kens 3y ago
Author here for any questions. Hopefully you're not tired of the 386 yet!
679.
by kens 3y ago
The retrocomputing question mentions the theory that upper case was selected because it would be disrespectful to put "God" in lower case. I remember reading that explanation decades ago on alt.folklore.computers, so the story has
680.
by kens 3y ago
The patent for the 6800 chip reveals some interesting features. Most curious is the slush maker shown in the drawing on the first page: https://patentimages.storage.googleapis.com/be/e4/fa/8e78e82... (The pat
681.
by kens 3y ago
Interestingly, the 8080 and 6800 were also designed more for embedded applications than for general-purpose computing. As late as 1981, Intel was focused on the various products that microprocessors could be designed into, such as clothes d
682.
by kens 3y ago
My view (based on a lot of RISC research) is that this isn't a meaningful question. As computer architect John Mashey said: there are CPUs for which RISC/CISC is probably not a very relevant classification, such as older CPUs or e
683.
by kens 3y ago
Looking at the 386 die, I think the decoded instruction queue consists of three parts widely separated on the die: the 32-bit immediate value stored in the datapath, the instruction fields in the middle of the chip, and the microcode start
684.
by kens 3y ago
rep_lodsb: Do you know what various undocumented things are in the 286 patent? In particular, the block diagram shows PHAM and LCM signals from the microcode, but they don't explain what these are. Maybe PHAM is physical memory? COREQ
685.
by kens 3y ago
Very interesting. The 386 patents (e.g. 4972338) don't have any useful details. I wonder if that's related to Intel's decision not to second-source the 386; maybe they decided to keep as much secret as possible.
686.
by kens 3y ago
Thanks for the comments. SLL and SLR are just my error (assuming that the acronym for Shift Logical Left was SLL); I've fixed the post. I don't know if I'll ever get to the microcode; it would be quite a project to figure it
687.
by kens 3y ago
Author here: what I find interesting about the 386 is that it is a complex chip (285,000 transistors), yet if you look at individual functional blocks, they can still be understood. On the other hand, looking at x86 circuitry makes me appre
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by kens 3y ago
There shouldn't be popups covering the screen. What browser/device are you using to view my website?
689.
by kens 3y ago
One lecture from 2004 discusses the buffered clock tree in the Alpha 21064 (1992), while the 386 (1985) didn't use them, so that gives a time period. As far as two phases, the lecture says that edge-triggered (rather than two-phase) is
690.
by kens 3y ago
I haven't looked at the 186, but maybe if I have time. From a quick look, it looks like the core is similar to the 8086 so the circuitry improvements can't be too major. It would be interesting to compare the microcode. And of cou

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