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* Posts by John Airey

8 publicly visible posts • joined 15 Aug 2006

Line up for parallelism

John Airey

Yeah but, no but

Parallel computing is a brilliant idea let down by one tiny problem. Humans. The trouble is we may have this really amazing brain (although you do meet people from time to time that cause you to question this) but we think in serial.

I used to do OCCAM programming of the Transputer. My head hurt trying to parallelise computations. In fact I'm probably still traumatised from the effort now, and that's about ten years later.

So unless we can raise a breed of programmers who think in parallel faultlessly then parallelism is pretty much doomed. We can't even get programmers who can write a perfect program in serial. Imagine the damage they could do in parallel!

I guess we could make a machine to do it, but how would we program it? Perhaps we should just build Skynet and have done with it?

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What is the purpose of tickling?

John Airey

Does tickling have anything to do with touch

My eight year old son will laugh uncontrollably if I put my hand close to his bare foot. I don't even have to touch him (although I'm holding his foot with my other hand). Try to explain that one, folks.

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Why do your hands turn white when you wash the dishes?

John Airey

Now I see

So basically, the idea that skin is waterproof is wrong. However, being the largest organ I think it's handy stuff. In fact, I wouldn't choose to live in anything else right now.

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What conditions disqualify you from donating blood?

John Airey

Explanation of Q12 NBS

I've been a blood donor for about twenty years, but I've made over 180 donations (including plasma and platelets). Question 12 has been around ever since AIDS cases first hit the news and relates to the historical fact that more homosexuals caught HIV than heterosexuals. This is no longer the case, but the question remains as an anomaly.

Now please don't scream homophobia because it's not pleasant to be as anti anti-gay as anti-gays were some years ago. In other words, it makes you a hypocrite. Also, homophobia is a made up word and criticising homosexuality (and for that matter, heterosexuality) isn't illegal. To be absolutely clear, inciting violence against anyone *is* illegal.

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The trouble with rounding floating point numbers

John Airey

Don't feed the trolls

Especially when they change their story from one post to another.

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John Airey

Paradox?

Eric, you have stated that the processor uses the HLT instruction, not the NOOP instruction. That's an instruction that it still has to process.

So what does it do after that? The next instruction of course.

And after that? The next instruction. And so on.

Were it to actually stop, how would it start again? This is not a marathon runner that has to stop for drinks every now and then, it's a CPU! The only processors I've ever seen stopping have been those affected by the F00F bug or faulty ones. I haven't even mentioned the processing of interrupts, which of course would be impossible if the CPU had stopped for a tea break.

First you said that the processor would get hotter, then you say it doesn't get hotter because your cooling is working. Which is it to be?

I suggest studying Computer Science would be most beneficial.

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John Airey

What - there are hotter instructions?

The anonymous poster above is one who clearly doesn't understand how PCs work. The "system idle" process is simply a "no operation" instruction being run by the CPU. It has not stopped processing at all. It's simply processing a "do nothing" instruction over and over again (which is a total waste of electricity). Only the F00F bug (or similar) actually stops the processor.

It's an important part of testing that all the instructions produce approximately the same amount of heat. Were there really instructions that made the CPU hotter then I could write a virus to set a computer on fire (some of the old commodore pets had a bug in their CPUs that allowed you to do something like this).

I've been running this mersenne prime code for over four years across numerous systems. I do not observe the CPUs are any hotter than when this code is not running. The only processor I have observed as being hotter was in fact a faulty one. The actual fault was only detected by using the software as it passed all other diagnostics. I only realised that it was running too hot when I saw how much cooler the replacement ran.

Please stop posting nonsense.

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John Airey

Automatic assumption of accuracy?

It has been assumed here that all CPUs are equally good at calculating floating point decimals to the accuracy we'd expect. However, if you have a faulty CPU it will not be able to add up correctly anyway. The first Pentium bug was as readers will recall was floating point problem.

Since the CPU itself cannot be trusted, the best solution for checking the accuracy of the CPU that I have found is using the Mersenne Prime code. Not only does this work as a constant test but you can use it to find memory and CPU problems. It costs nothing in terms of processing as the code takes the place of the "idle" process. (Sadly there are people who think that CPUs do not run all the time, which means they do not understand the Von Neumann architecture).

Details at www.mersenne.org.

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