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Half of Germany's Power Supplied By Solar, Briefly

enriquevagu Gigawatts per hour (461 comments)

Note that gigawatts are power units; gigawattshour are energy units and gigawatts per hour is wrong and misleading. I would expect that the editor would correct such basic mistakes, even tough they come from the linked article.

about a month ago
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Researchers Unveil Experimental 36-Core Chip

enriquevagu Re:Is there anything new here? (143 comments)

Some knowledge about multicore cache coherence here. You are completely right, Slashdot's summary does not introduce any novel idea. In fact, a cache-coherent mesh-based multicore system with one router associated to each core was presented on the market years ago by a startup from MIT, Tilera. Also, the article claims that today's cores are connected by a single shared bus -- that's far outdated, since most processors today employ some form of switched communication (an arbitrated ring, a single crossbar, a mesh of routers, etc).

What the actual ISCA paper presents is a novel mechanism to guarantee total ordering on a distributed network. Essentially, when your network is distributed (i.e., not a single shared bus, basically most current on-chip network) there are several problems with guaranteeing ordering: i) it is really hard to provide a global ordering of messages (like a bus) without making all messages cross a single centralized point which becomes a bottleneck, and ii) if you employ adaptive routing, it is impossible to provide point-to-point ordering of messages.

Coherence messages are divided in different classes in order to prevent deadlock. Depending on the coherence protocol implementation, messages of certain classes need to be delivered in order between the same pair of endpoints, and for this, some of the virtual networks can require static routing (e.g. Dimension-Ordered Routing in a mesh). Note a "virtual network" is a subset of the network resources which is used by the different classes of coherence messages to prevent deadlock. This is a remedy for the second problem. However, a network that provided global ordering would allow for potentially huge simplifications of the coherence mechanisms, since many races would disappear (the devil is in the details), and a snoopy mechanism would be possible -- as they implement. Additionally, this might also impact the consistency model. In fact, their model implements sequential consistency, which is the most restrictive -- yet simple to reason about -- consistency model.

Disclaimer: I am not affiliated with their research group, and in fact, I have not read the paper in detail.

about a month ago
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WikiLeaks: NSA Recording All Telephone Calls In Afghanistan

enriquevagu Technical details? (241 comments)

Just curiosity... The bandwidth required to do this should be enormous, how did they implement it? Are the trunk switches compromised and they locally record every conversation, and later send it to the USA? Did they install dedicated fibers to do this? TFA lacks any details.

Thanks.

about 2 months ago
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New Cologne Answers the Question: "What Does a Bitcoin Smell Like?"

enriquevagu Free advertisement (61 comments)

Invent anything you want to sell, name it after bitcoin and you receive free advertisement in Slashdot front page!

about 3 months ago
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Intel and SGI Test Full-Immersion Cooling For Servers

enriquevagu Re:I doubt it (102 comments)

This post is incomplete because of problems with html markings. Please see the complete post below (and mod this one down!)

about 4 months ago
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Intel and SGI Test Full-Immersion Cooling For Servers

enriquevagu I doubt it (102 comments)

(sorry for the duplicated posting; the previous one was cut because of problems with the html marks)

In order to obtain a 90% reduction in the energy bill, cooling must account for 90% of the power of the DC. This implies a PUE >= 10. As a reference, 5 years ago virtually any DC had a PUE lower than 3. Nowadays, PUE lower than 1.15 can be obtained easily. As a referecence, Facebook publishes the instantaneous PUE of one of its DC in Prineville, which at the moment is 1.05. This implies that any savings in cooling would reduce the bill, at much, in a factor of 1.05 (1/1.05 = 0.9523).

On the other hand, I believe that this is not the first commertial offer for a liquid-cooled server, Intel was already considering two years ago, and the idea has been discussed in other forums for several years. I can't remember right now which company that was actually selling these solutions, but I believe it was already in the market.

about 4 months ago
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Intel and SGI Test Full-Immersion Cooling For Servers

enriquevagu I doubt it (102 comments)

In order to obtain a 90% reduction in the energy bill, cooling must account for 90% of the power of the DC. This implies a PUE >= 10. As a reference, 5 years ago virtually any DC had a PUE instantaneous PUE of one of its DC in Prineville, which at the moment is 1.05. This implies that any savings in cooling would reduce the bill, at much, in a factor of 1.05 (1/1.05 = 0.9523).

On the other hand, I believe that this is not the first commertial offer for a liquid-cooled server, Intel was already considering it two years ago, and the idea has been discussed in other forums for several years. I can't remember right now which company that was actually selling these solutions, but I believe it was already in the market.

about 4 months ago
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Don't Help Your Kids With Their Homework

enriquevagu Homework are part of the learning process (278 comments)

Homework is part of the learning process; helping with homework prevents the kid from doing them and, in the process, learning. Solving math problems for homework, as an example, is not because the teacher wants to know the final answer; it's because the teacher wants the student to confront a new type problem and, in the process of confronting it and guessing how to obtain the solution, learn. I give detailed solutions to the class problems to my undergraduate students (they would obtain them anyway, and in many cases with errors), but I always insist that looking at the solution should be the last resort if they don't know how to face the problem (solutions are intended for checking their own's).

The problem with external help (from the parents, typically) is that, in many cases, the parents get involved in excess and actually do the homework for their sons, so the teacher cannot find any error in the child's results. I know a case of a mother who was doing exactly this, because his kid didn't get very good grades (I was even asked for help in some work the child had to do for school with the computer!). The grades started getting worse and, three years later, the kid was in special education. I know this is not the only reason, but I'm confident it affects a lot.

about 4 months ago
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How Do You Backup 20TB of Data?

enriquevagu Classification, first step (983 comments)

The first step is to classify the data in two groups: what you would not want to lose at any cost, and the redundant data (movies, music, etc) that you could survive without. This is the most important step

The second step is to backup the important data using an external 1 TB drive, tape or similar.

Optionally, the third step is to delete the remaining 19 TB.

about 5 months ago
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Scientific Data Disappears At Alarming Rate, 80% Lost In Two Decades

enriquevagu Our approach in our research group (189 comments)

This problem occurs even for people in the same group, who often find problems to repeat the simulations from our own papers, and even as recent as one year ago. The problems typically come from people leaving (PhD finished, grants that expire, people that move to a different job), changes in the simulation tools, etc.

In our Computer Architecture research group we employ Mercurial for versioning the simulator code. Thus, we can know when each change was applied. For each simulation, we store both the configuration file that is used to generate that simulation (which also includes the Mercurial version of the code which is being used) and the simulation results, or at least only the interesting results. Multiple simulators allow for different verbosity levels, and in most cases most of the output is useless, so we typically store the interesting data (such as latency and throughput) because otherwise we would have no disk space.

Even with this setup, we often find problems trying to replicate the exact results of our own previous papers, for example because of poor documentation (this is typical in research, since homebrew simulation tools are not maintained as one would expect from commertial code), changes that introduce subtle effects, code that gets lost when some person leaves or simply large files that get deleted to save disk space (for example, simulation checkpoints or network traces, which are typically very large).

However, you typically do not need to look back and replicate results, so keeping all the data is a useless effort. I completely understand that research data gets lost, but I think that it is largely unavoidable.

about 7 months ago
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IE Zero-Day Exploit Disappears On Reboot

enriquevagu Dissapears on reboot... (103 comments)

Sure it dissapears!

Unless you're running IE as admin, you have UAC disabled and the malware has installed a hypervisor and you're hickjacked forever without having any chance to detect it. How long before we see that?

about 9 months ago
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VLC Reaches 2.1

enriquevagu Turning off the computer (127 comments)

Yet still it does not support turning off the computer, despite being a feature requested for years. That's the ONLY missing feature which prevents it from being my default video player

about 10 months ago
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LGPL H.265 Codec Implementation Available; Encoding To Come Later

enriquevagu Decoder, not codec (141 comments)

CODEC: COder-DECoder; but there is no (en)COder here!

about a year ago
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EFF Slams Google Fiber For Banning Servers On Its Network

enriquevagu Server description (301 comments)

all ISPs are deliberately vague about what qualifies as a 'server.' ... because TCP clearly specifies it.

The fact that some programs might behave correctly when implementing a server, or not (eg: skype) or the fact that, in some cases, ISPs allow certain services or ports, does not mean that a 'server' is something arcane. It's you that don't know it.

about a year ago
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Computer Memory Can Be Read With a Flash of Light

enriquevagu Comparison to PCM (69 comments)

The link to the actual Nature Communications paper is here: Non-volatile memory based on the ferroelectric photovoltaic effect.

This somehow resembles Phase-Change Memory (PCM). PCM devices are composed of a material which, under a high current, there is a thermal fusion and changes to a different material status, from amorphous to crystalline. This changes two properties: light reflectivity (exploited in CDs and DVDs) and electrical resistance (exploited in emerging non-volatile PCM memories). The paper cites PCM and other types of emerging non-volating memories.

In this case, it is the polarization what changes, without requiring a thermal fusion, therefore increasing the endurance of the device, one of the main shortcomings of PCM. The other main shortcoming of PCM is write speed due to the slow thermal process, in the paper they claim something like 10ns. If this can be manufactured with a large scale of integration and low cost, it will probably be a revolution in computer architecture.

about a year ago
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Supercomputers At TACC Getting a Speed Boost

enriquevagu Units (14 comments)

GB != Gbps.

about a year ago
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Major Advance Towards a Proof of the Twin Prime Conjecture

enriquevagu Conclusion wrong (248 comments)

"the existence of any finite bound, no matter how large, means that that the gaps between consecutive numbers don't keep growing forever"

Actually, I disagree with the unfortunate writing of the sentence. The gaps between consecutive prime numbers are variable, and on average they DO tend to keep growing forever. This is a widely known result, the density of prime numbers decreases as the numbers grow. However, since the gap between consecutive primes is variable and it does not follow a regular function (otherwise, it would be very easy to calculate prime numbers), even with a very low density of prime numbers we can find a pair of consecutive prime numbers with a gap of only 2.

The problem under study is not wether the gap between consecutive primes keeps growing forever (which is true only on average, considering a long secuence of integers), but wether there are infinite such pairs of primes with gap 2. The new result found says that there exist infinite pairs of primes with gap 70M or less. However, this does not imply at all that no consecutive pairs of primes with gap > 70M exist (which, in fact, they do).

about a year ago
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UK Researchers Build Micron LED Light Based Wireless Network

enriquevagu NRZ coding (70 comments)

C'on, this is Slashdot. Is it so complex to say that they employ an NRZ modulation using a light carrier, rather than "a bit like Morse Code from a torch"? Is it so difficult to refere to the switching/modulation frequency, or baud rate, rather than "they can also flicker on and off around 1,000 times quicker than the larger LEDs"?

The idea of using a LED light for communication is presented as a novelty in the summary, when all remotes work this way, and even the original 802.11 specs included a PHY layer that relied on IR. You are trying to make articles more dumb-user-friendly, but what you are getting is to kick out the users that might make valuable comments.

about a year and a half ago
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"Bill Shocker" Malware Controls 620,000 Android Phones In China

enriquevagu Not a virus; virus self-replicate (138 comments)

This is NOT a virus; viruses infect a system, typically by modifying other existan executable files, and then self-replicate themselves. These are malware applications which have been installed by the users. In this case he notice, not covered in the summary, is that these applications are not designed to be malware, but rather they employ a free (as in gratis) SDK, which converts the phone in a zombie.

However, note that simply removing the applications should remove the "infection". The Android security model does not allow an application to "infect" the OS, unless the user has rooted the phone and runs the application as root (in this case, it's your fault).

about a year and a half ago

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