Please create an account to participate in the Slashdot moderation system

 



Forgot your password?
typodupeerror
×

Comment Re:What am I missing? (Score 2) 255

See, I think they should fall up. Antiparticles are predicted by the negative energy solutions of the Dirac equation.

But they still have positive energy. (Think of them as "holes" in a sea of negative-energy electrons; kick an electron out of that sea and you get a positive-energy negatively-charged electron and a positive-energy positively-charged "hole", i.e . a positron.)

Comment Re:I must be stupid (Score 4, Informative) 255

However, this is not how we have traditionally defined anti-matter; the original definition was actually due to the fact that the universe has significantly less mass than it should, and "anti-matter" was hypothesized as an explanation.

Actually, the original modern definition of anti-matter was "Dirac's relativistic equation for the wave function of the electron had negative energy states as well as positive energy states, which was a bit weird, so it was proposed that all the negative energy states were filled, and if you knocked an electron out of one of the low-energy states, a "hole" would be left behind, and that hole behaved like an electron, except that it has a positive charge". It was later seen in the real world (particles moved in a magnetic field as if they had the mass of an electron and a +1 electrical charge). See, for example, the Wikipedia article about the positron.

Comment Re:Oh, good (Score 1) 219

Correlation does equal causation, both statements are true. Just missing some conditions there. Say you repeatedly hit your head with a hammer, it would be right to correlate it with the pain in your head. But if your were walking, saw a shooting star and felt a pain in your left knee, no that does mean the shooting star caused it.

"Repeatedly" is the key word there. A one-time incident with a shooting star and a pain in your left knee doesn't give much of a "correlation"; you need a few more data points for that.

And a more precise version of what should be meant by "correlation is not causation" is "if A and B are correlated, that, by itself, is insufficient to suggest that A causes B, given that the same correlation would show up if B caused A or if C caused both A and B". The "conditions" in your first example are what let you conclude that "A causes B" is the most likely case.

(If somebody were able to make their headache go away by hitting themselves on the head with a hammer, that might be a case of "B causes A" there, but that would be a case of the pain coming first and the hitting-yourself-on-the-head coming later; if somebody were to have a neurological disorder that 1) caused pain in the head and 2) caused an impulse to hit himself or herself on the head with a hammer, that would be a case of "C causes A and B", but, in that case, the pain would probably happen before he or she hit himself or herself on the head.)

Comment Re:Whatever! PowerPC been doing 64-bit (Score 1) 332

Opteron ought to be compared to POWER, not PowerPC, given the target markets.

Presumably referring to, as per the distinction I drew in "Both POWER (all-caps) and PowerPC refer both to instruction set architectures and brand names used on processors that implemented them.", POWER and PowerPC the brand names used on processors, not POWER and PowerPC the instruction set architectures.

Also, in the Windows world itself, you had 64-bit MIPS and Alpha based workstations that ran NT...

...which was a 32-bit OS, so it didn't provide 64-bit computing on those 64-bit processors.

Comment Re:Whatever! PowerPC been doing 64-bit (Score 1) 332

Seeing as the PowerPC 970 ("G5") was the first 64-bit PowerPC (not POWER, though) processor, even the Opteron came out before the first 64-bit PowerPC.

As I said in an earlier post in this thread, "Both POWER (all-caps) and PowerPC refer both to instruction set architectures and brand names used on processors that implemented them."

If "the first 64-bit PowerPC" refers to PowerPC-the-brand, yes, the first one (other than the 620, which wasn't made in large quantities) was the 970.

If it refers to PowerPC-the-instruction-set, the first one was the POWER3 - it implemented the full PowerPC instruction set (as well as the POWER2 version of the POWER instruction set).

Comment Re:Did it really work? (Score 1) 332

I suppose it depends on how you look at it. If you view the page directory as a bank select then it is a sort of segmentation.

If you view the page directory as a bank select then any form of paging with more than two levels of page table is a sort of segmentation, including x86 paging without PAE (all the way back to the 80386), and the form of paging on just about every modern processor.

Comment Re:Whatever! PowerPC been doing 64-bit (Score 1) 332

And how many people actually owned a SPARC, POWER, or Itanic for that matter?

Well, some of the masses might have had G5 iMacs (PowerPC 970, 64-bit), but, yes, it took AMD to bring 64-bit to most of the masses.

At least one comment claims that the original title of the article was "64-bit Computing Reaches 10th Anniversary", which, if true, means the article came out with a bogus headline (there's more to "Computing" than stuff that runs on a mainstream desktop or laptop machine, and DEC OSF/1 came out in 1993, so it's been at least 20 years); if the original comment was posted before that, I can see his complaint (and the complaint of the person who pointed out that the MIPS R4000 came out before the first 64-bit PowerPC processor). Complaining about "64-bit x86 Computing Reaches 10th Anniversary" neglecting other 64-bit architectures, however, is silly.

Comment Re:Did it really work? (Score 1) 332

64-bit binaries are larger and might run 103% at the speed of 32-bit if you're lucky.

Maybe there is a lot of software written in C that uses int or unsigned when it should have typedef'd a size appropriate for its needs.

Software that's written in C, in all of the environments I know of for x86, has 32-bit ints (signed or unsigned) whether compiled 32-bit or 64-bit, so you're presumably not saying that those programs suddenly get 64-bit ints when compiled 64-bit. They will get 64-bit longs on UN*X (but not on Windows), and will get 64-bit pointers in either case.

Comment Re:Whatever! PowerPC been doing 64-bit (Score 2) 332

POWER != PowerPC

Both POWER (all-caps) and PowerPC refer both to instruction set architectures and brand names used on processors that implemented them.

The PowerPC ISA took the POWER ISA, added some stuff such as general-register-based multiply and divide instructions, and removed a few instructions (and didn't add in the ones used in the POWER2 processor).

POWER3 was a 64-bit processor that implemented the union of 64-bit PowerPC and POWER; I don't know whether any subsequent POWERn processors implemented the POWER ISA-only instructions or just the current version of the PowerPC/Power (not all-caps) ISA.

Slashdot Top Deals

Nothing happens.

Working...