Fair enough, a cable was involved. They didn't lower it to the ground on a cable. They didn't lower it while in powered flight hovering above the ground. They did it to separate the rover housing from the descent stage so it would have room to deploy the airbags. Compare to the Curiosity EDL and the operation is quite different.
Alpha designers worked on Alpha at HP -- they produced several variants of the EV7 there. And the servers based on those chips performed better than HP's Itanium offerings, which was rather awkward for them.
Dirk Meyer went to AMD long before that. It was still DEC when he left. Dirk was the lead architect of the K7 (that success being a big part of how he ended up in a position to become CEO) which came out while Compaq was still making new Alphas.
But you're right that a great many jumped ship from Compaq.
You're being completely revisionist.
No, just uninformed about the extent of the embedded use of these chips. By the time I heard of them (e.g. Playstation/N64, and much more recent uses of SPARC) their heydey was over. I had no idea there was a SPARC-based camera in the mid 90s. Obviously I was much more in tune with their traditional business side.
Some of these ISAs found new life, but MIPS and SPARC were for SGI boxes running Ultrix and Sun boxes running SunOS/Solaris respectively for many years. It's only once the original business models collapsed that they became otherwise.
NT on Alpha was contemporary with the ISA's hey-dey, though all it really did was demonstrate that you shouldn't count on Microsoft for the success of your non-x86 server platform. I did know someone who used such a box though. Four processors, baby!
Oh and yeah, the 68k is awesome. It was used in so much stuff besides machines running Unix, though, that "Unix processor" isn't an accurate historical metaphor.
Yeah, even some of the new parts weren't that new, though doing aerodynamic flight in Mars atmosphere counts as fairly new if not unprecedented.
The Viking's last stage of descent was done entirely with retrorockets on the lander itself. The MER rovers used a rocket powered descent stage that then dropped the rovers in their airbag-lined shells only the last 10s of meters. MSL was closer to the MER rovers in this sense, however the Sky Crane part was still completely new.
Spirit and Opportunity were dropped from their "sky cranes" (yes, they had them too, but they weren't called sky cranes at the time) from several storeys up,
They had a rocket-powered descent stage, but it wasn't a "sky crane" because it didn't lower them on a cable, ala a crane, thus why it wasn't called one.
Yes. If anything, Curiosity had it easy. It was placed ever so gently on the surface.
Easier on the rover by design/necessity, though more complicated for the EDL team. Not ridiculously so like everyone thought, but definitely a source of complication and stress.
I didn't realize it when I was watching the EDL stream live, but later learned that they had agreed that, largely due to the public watching, they had to be careful how they called out the steps of the landing. Specifically they said "TD nominal" when telemetry said the wheels were on the ground rather than "Touch Down" because they didn't want to get the public excited when the next thing telemetry told them could have been that Curiosity was being dragged across the surface of Mars by the descent stage after a failure to release the cables. They waited until they were sure Curiosity wasn't moving before declaring "Touch Down Confirmed."
Oh man, still gets me a little thinking about those words. Hehe.
Heh. What I like about the MSL pessimism is that most people didn't realize that literally the only new parts of the landing procedure were the sky crane at the end, and aerodynamic flight before parachute deploy.
It's like they think Spirit and Opportunity were just dropping onto Mars from orbit and some measely air bags absorbed all that energy.
But that's how Mission to Mars showed it, so I guess that's legit!
I suspect that part of the reason Intel invented Itanium is that a totally new and very weird architecture means a new set of patents for the core stuff that you need to make a processor which can run user mode code written to the standard ABI.
Patents with a fresh 17 year expiration date and not covered by licensing agreements with AMD et. al... Yes, I'm quite certain you are correct.
Heh. Given the intimate relationship between the proprietary Unix vendors and their proprietary RISC chips it's not completely bonkers to call em that. I mean did a PA-RISC chip have any purpose besides running HPUX? And did HPUX have any purpose besides being the Unix you got when you bought your PA-RISC systems?
That's an honest question; I've never seen a machine that had one without the other. I'm sure someone runs NetBSD or Linux on it but as far as market presence...
The writing was on the wall for the proprietary RISCs already as x86 ate their lunch from below. The main thing that was different in this respect was the amount of silicon they threw at Itanium. Give Xenons giant caches (and a non-shit bus) and they would have had the same effect of just completing the process that had already started.
The big wild card is HP. Itanium thoroughly killed Alpha because the half of the Alpha team Intel got obviously wasn't going to work on Alpha, while the half HP got was still doing good work but HP's commitment to Itanium meant they were actually down-playing the performance of their own Alpha servers.
I am pretty sure that Intel did not intend for Itanium to fail in the market, but in retrospect the outcome for Intel has been close to perfect.
Kinda true, but not really. As a consequence of the time wasted pursuing IA-64, AMD was able to beat them to market with 64-bit extensions to x86 making excluding them from the future of the x86 market impossible, while simultaneously jumping ahead in desktop and x86 servers, slashing the margins for Xenon.
Certainly it's not all downside for Intel. But it was a misstep and nothing like what they planned. If it weren't for their illegal business dealings that limited AMD's ability to take advantage, it would have been a disaster for them.
And now x86 machines are RISC too. IIRC all the x86 chips translate the x86 instructions into RISC instructions, with a little bit of optimization for their own RISC instruction set. The x86 instruction set, in some ways, simple allows for convenient optimization into the RISC instruction sets, and the option to change them in the background as use priories change.
Yes to the first part (the AC is correct in that it's technically microcode and not x86-anything, but you do have the gist), not so much the second. See, most compilers/programmers use a very RISC-like subset of x86. Most of the micro-arch optimization is thus of the kind you'd do in a RISC isa too -- like if you have 256-bit vector FP in your ISA, but only 128-bit functional units, you'd split the one inst into two micro-ops in either case.
The one big exception is REP MOV. This basically gives the architects the ability to write the best copy algorithm they can for that particular microarchitecture. Which is nice to have.
It's been a long time since I dug into Linux kernel internals, but I remember seeing a routine at start-up that would try various memcpy algorithms, including on x86 rep movs. At the time (late 90s) I don't think much effort was put into optimizing the microcode for REP MOV, and linux would (on my machine) always choose something else. I wonder if this is changed and REP MOV is consistently winning, or if other instruction-level algorithms can do better in some cases.
ARM is a really nice design, very extensible and very RISC
It has fixed instruction length and load/store architecture, the two crucial components of RISC imo, but doesn't go "very" imo. The more I learn about ARM, the more delirious my laughter gets as I think that this of all RISC ISAs is the one that is poised to overturn x86.
For example, it has a flags register. A flags register! Oh man, I cackled when I heard that. I must have sounded very disturbed. Which I was, since only moments before I was envisioning life without that particular albatross hanging around my neck. But I guess x86 wasn't the only architecture built around tradeoffs for scalar minimally-pipelined in-order machines.
Well whatever. The long and short of it is that ISA doesn't matter all that much. It wasn't the ISA that made those Acorn boxes faster than x86 chips. The ISA is limiting x86 in that the amount of energy spent decoding is non-negligible at the lowest power envelopes. In even only somewhat constrained systems it does just fine.
Oh and on the topic of Intel killing x86 -- they don't really want to kill x86. x86 has done great things for them, with both patents and it's general insane difficulty to implement creating huge barriers to entry for others helping them maintain their monopoly. Their only serious move to ditch x86 in the markets where x86 was making them tons of money (as opposed to dabbling in embedded markets) was IA64, and the whole reason for that was that then AMD and Via wouldn't have licenses to make compatible chips.
Causality means that any transmission of information from event A to event B means that event A must precede B in time. An example would be an electron emitter emitting an electron, and a detector detecting an electron. If the detector went off before the electron was emitted, that would be a violation of causality.
Relativity of simultaneity does nothing to prevent such a global evaluation, it only restricts the sets of events that could possibly be causes of other events.
As long as events A and B are separated by a time-like distance, then while individual observers may disagree on the exact timing of A and B, all will agree on their ordering. It's only when A and B are separated by space-like distances that different observers will disagree on their ordering. And therefore, if it was possible to send information that could get outside of your future light-cone, then that information could be relayed around between several reference frames and back to you, arriving before you sent it in the first place according to all observers, creating a paradox.
This is the foundation of the argument against FTL information transfer, the Paradox in the EPR Paradox. It's why it's important for maintaining QM's consistency with Special Relativity that quantum entanglement is not capable of sending information.
The circumstances that allow time paradoxes in Special Relativity while allowing FTL communication are somewhat exotic. If we just allow retrograde causality in any given experiment then it should become trivial to create a paradox. Alice conducts and experiment that transmits information Bob. After receiving the result, Bob conducts his experiment which sends information in the opposite time direction back to Alice prior to her conducting her experiment. As per their previously agreed upon protocol, if Alice receives information from Bob she does not conduct her experiment. Paradox.
There's no requirement that one direction in time be singled out as special, but whichever way you go everything else should be going in the same direction. If you time reverse the evolution of the solar system everything works, but not if you only reverse time for the Moon while the rest of the solar system evolves in the usual direction. Can anything but our experience/the 2nd law say that one is the "future" and one the "past". No, but if you picked one by arbitrary convention, then everyone else would have to agree.
If there's a form of retrocausality that allows it to occur with respect to other forward-causality events without allowing for paradoxes, that'd be quite interesting.
Schrodinger wasn't making a point about quantum theory, just the copenhagen interpretation.
The ridiculous result he posited only applied to the Copenhagen interpretation, but parts of how he arrived there, which he was also pointing out as problems, applied to QM in general. Like the concept and exact point of "measurement" being poorly defined.
If you looked at his thought experiment today, you'd say that the point where the detector either registered a hit from the radioactive decay, or didn't, was a measurement that collapsed the wave function. Interacting in a way that can influence an experiment is a measurement -- avoiding doing so until the desired time is a big part of the challenge of quantum computers.
Part of the unintended but sad legacy of Schrodinger's Cat is that by depicting a scenario where measurement by a device, release of a cloud of chemicals, interaction with the metabolism of a cat, and the death-throws of the cat do not count as measurement, but a researcher opening up the box of the cat does, it's led to the idea that "measurement" means only "observation" which can only be done by an "observer" which is a sentient human being and not a cat. Thus resulting in so much of the Woo-woo that bastardizes QM.
Anyway, I don't see what's so absurd about the Copenhagen Interpretation. It's basically taking the sum-of-histories method of calculating the predicted result of a quantum measurement and saying that, yes, the particle really followed all those histories. Apparent self-interference is the consequence of actual self-interference.
You've given this silly scene far more thought than most sane people.
Ah, see, that's the secret. Sanity is crutch that's also a shackle.
"A car is just a big purse on wheels." -- Johanna Reynolds
