How The 360 Works

The always informative How Stuff Works site has an article today entitled How the Xbox 360 Works. From the piece: "The other interesting thing to note about the Xbox 360 CPU is that each core is capable of processing two threads simultaneously. Think of a thread as a set of instructions for a program's job. The core processes these instructions and does the heavy lifting to get the job done. A conventional processor is traditionally capable of running a single execution thread. Because the Xbox 360 cores can each handle two threads at a time, the 360 CPU is the equivalent of having six conventional processors in one machine."

I thought it _didn't_ work?

[cryptoz]

I thought something like 15% of Xbox's *didn't* work. Source? Slashdot. Surprise, surprise. It's funny. Laugh.

Wht makes Xbox run

[Gilzors]

4 words: A wizard did it.

Re:Wht makes Xbox run

[Mad_Rain]

4 words: A wizard did it.

bloodninja: Oh yeah, aight. Aight, I put on my robe and wizard hat.

sigh, what is this, TV ?

[DrSkwid]

"Because the Xbox 360 cores can each handle two threads at a time, the 360 CPU is the equivalent of having six conventional processors in one machine."

No it isn't.

Re:sigh, what is this, TV ?

[drinkypoo]

OK, smartass, but at least explain _why_ it isn't.

Why? Because most processors are already superscalar, because there is a single data path for all three cores, and because a single processor has a single context (unless it's hyperthreading, and has two contexts) and multiple processors have multiple contexts.

Am I a whore yet?

Re:sigh, what is this, TV ?

[panth0r]

Am I a whore yet?

Yessa. But on an otherwise unrelated note, I heard there was this Target store that was opening up at 7:30 AM this morning, and they only had four of the damn things, and the store decided not to tell anyone in line of this fact, as a matter of fact, when the line was up to around 10 people, they explictly told the employees not to tell them this, and this was at 10:30 at night. They also didn't offer any sort of rain cheque or anything, if you weren't the first in line, you di

Re:sigh, what is this, TV ?

[jmcneill]

That's hilarious. A cow orker was telling me today about one of the local EB Games stores in the city. Rumour has it that they had received 18 consoles, and at the end of the first day they still had 13 left!

Put a smile on my face when I heard the news this morning; not that I plan on buying one, but it appears that at least in this area, either people didn't buy the hype or we're completely bass-ackwords :)

Re:sigh, what is this, TV ?

[Poltras]

What exactly is a cow orker?

Re:sigh, what is this, TV ?

[bonhomme1]

In Soviet Russia the whores have multiplecontexts

Razor blade star NUMA NUMA yay

[tepples]

All the CPUs have to share access to memory, especially if one CPU is locking part of the cache for a big signal processing job. The bottleneck at the memory controller keeps SMP (symmetric multiprocessing) from reaching its theoretical throughput.

In order to get true performance out of a multicore system, you have to use NUMA, which is not just part of the hook from a Romanian pop song [wikipedia.org]. It stands for non-uniform memory access [wikipedia.org], and it refers to associating a physical memory chip to each CPU. It's "non-uniform" because it takes longer for a CPU to read or write another CPU's memory than to read or write its own. But running threads that don't need to communicate too much and putting their memory on separate cores does ease up on the memory controller bottleneck.

Re:Razor blade star NUMA NUMA yay

[oliverthered]

but isn't one of the benifits of running multiple threas per CPU that while one thread is waiting for memory another can be executing, helping redress the ballence without NUMA

So that makes it....

[Anonymous Coward]

...A CELL!

More like 3.90 processors

[acidrain]

Because the two threads in the chips share arithmetic and floating point units and whatnot, they get best case throughput of 1.3x a single threaded chip. This is according to Sony who has the same PPU on their PS3.

Re:More like 3.90 processors

[iota]

> Because the two threads in the chips share arithmetic and floating point units and whatnot,
> they get best case throughput of 1.3x a single threaded chip. This is according to Sony who has the same PPU on their PS3.

I don't mean to be too pedantic here, but you are not correct.

The Cell PPU unit and the XBOX360 PPC unit are not the same. They are related by the fact that they are both PPC designs, but that is as far as it goes. The XBOX360 PPC has two fixed-point, two floating-point and two VMX units per core - thread switching is done on fetch stalls. The Cell PPU has two register files but only single fixed-point, floating-point and VMX units - threading is accomplished by switching between the register files. The branch prediction units are also different, and the caches, and the memory mapping. As a matter of fact, the only thing the two processors share is an instruction set and an IBM invoice.

The number you (mis-)quote originally came from a lecture in an SCEA conference. You apparently don't understand the context under which it was said, and thus why it makes no sense to discuss here - nor do you appear to understand the NDA which, if you heard this directly from SCEA, are under. Although much of the Cell design and tools are public knowledge, it is necessary to keep confidential that non-public information which you have access to if you wish to continue to have access to it.

How Websites Make Money

[Saeed al-Sahaf]

Wonder if How Things Work got paid for that?

Re:How Websites Make Money

[Keeper]

Sure they did. Probably the same way Slashdot gets paid for posting a link to it.

Really?

[oahazmatt]

That's how it works? And here I thought it was just the latest console using Hype technology.

Re:Really?

[FidelCatsro]

I believe the Xbox 360 can perform 3.6 MHpF (Mega-hypes per fact ). The marketing team sat for the last 6 months optimising the performance of the facts ..The new technology breakthrough was thanks to an unprecedented runaway budget and an amazing amount of bullshit performance optimisations

Worthless site

[scot4875]

After reading the how the XBox 360 works, I checked out a couple other systems.

None of them had any details about how any of the systems actually worked; it was just a list of marketing bullet-points and features published by the manufacturers.

How does knowing the system's launch lineup help me know how it works, anyway?

As for things that were flat out wrong about the 360...

9 billion dot products per second? Are they claiming that each core can compute a dot product at nearly every cycle? And if so, how is that number helpful? You still have a ton of other stuff to do in a game engine besides just computing dot products.

1 teraflop? Each thread on each core can calculate 166 billion FLOPS? Oh wait, you mean that you're also counting GPU performance in that number, which accounts for probably .999 teraflops?

500 million triangles per second... With how many textures applied? How many light sources? Oh, zero textures, using flat shading, with no light sources? And all 500 million triangles are part of a single triangle strip and are each 1 pixel in size? And that's just the theoretical maximum anyway?

What a worthless site. I feel dumber for having read it.

--Jeremy

Re:Worthless site

[grahamwest]

The Xbox360 core does have a dot product instruction with 1 cycle of throughput so technically the article is correct about that.

Your wider point is well made, however.

Micro$oft at it's best!

[Electr!c_B4rd_Qu!nn]

I swear, Bill Gate$ and his cronies are definately pulling all the propaganda strings on this one. I'll admit, I'm a fan of the XBoX, but not of it's 360 counterpart. I believe that the console was rushed out the door as fast as possible with enough marketing pusking behind it to possibly sell it as the next Messiah of console. The damn thing CRASHED when it was released, I don't care how wowie-zowie it is. That means one thing to me, it's broken on delivery. Now sadly, I'll have to find a different conso

Re:Micro$oft at it's best!

[Parham]

I'll write that it's an impressive system, and that the games look good. I have nothing against the system itself, but what I do have a problem with is the marketing behind the system. Several people I know are just plain angry that they couldn't get their hands on one because it sold out and they have to wait a long while to even get one. They hyped a system, and then didn't have enough to sell (intentionally [slashdot.org]), that's what's so upsettting to me.

Respect where respect is due

[SalaciousPucker]

It's like a reflex action to bash Microsoft here. First off, quality is always shaky on the first batch of any gaming console. It's a business where the hardware launches are historically tight. The only company that releases solid, well built, well tested consoles at launch is Nintendo, and look where their share of the market has gone. Second, based on everything I've read about the XBOX 360 it has a solid, almost textbook design, for the best technology of the next 5 years (multi core processor, unified pipeline shader/vertex on the graphics card, etc). I see alot more to question about the PS3's cell (limitations of SPE's etc) & the late addition of NVidia, since Sony only pulled them into the PS3 when they realized the Cell wouldn't be able to do the GPU work. Need I remind everyone that you are bashing a 3-GHZ G5 w/ 3 Core's paired with ATI's finest and all for $400? Yes, the marketing BS is just that, but if this was anyone else's product it would get treated alot better.

Re:Respect where respect is due

[Keeper]

Ah yes, I have many fond memories of attempting to blow dust out of connectors ... I miss the simpler times of the NES.

News for...who?

[afabbro]

Think of a thread as a set of instructions for a program's job.

Now really, if you're reading this site, you should know what a thread is, for pity's sake...and if you didn't, now you certainly don't because that's not a good definition.

Should popular mechanics explain what a combustion engine is? Is this news for nerd-wannabes?

Re:News for...who?

[Sinryc]

Its news for nerds, but nerds come in all shapes, sizes, and types.... There are you videogame nerds... Your computer nerds... Your astology nerds... Your biology nerds... there are all kindsa nerds, remember that.

Re:News for...who?

[Patrik_AKA_RedX]

"Think of a thread as a set of instructions for a program's job."

Worst definition of the day.

"Think of a thread as a routine that runs on his own, while the rest of the program continues as normal." would be a little closer. The original definition sounds more like a routine than as a thread.

Better Summary

[talksinmaths]

The Onion has a summary [theonion.com] that is just as informative and much shorter.

Lets all be honest...

[richman555]

At the end of the day, all of this talk about threads in these processors will be a wash. In fact, I'll bet that most titles won't take advantage of it. Developers will find this to be a real pita to program and will cost them a good amount of time and money. It all sounds great in theory, but thats just theory. At the end of the day, people will realize that these machines are not super computers and their benefits will be outweighed by their cost.

So?

[Tom]

So what, if it still just crashes [slashdot.org]? In fact, this might be one of the reasons. Why can't M$ "innovate" (i.e. play catch-up with the real innovators) somewhere safe first? Wait, that's exactly what it is! Everyone else innovates first and goes to market second. M$ goes to market first, and does alpha testing in public, that way they're usually only slightly beyond and appear innovative.