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Old 2016-01-25, 04:07   #1
jschwar313
 
"Jim Schwartz"
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Default New to GIMPS. What is a GPU?

Is it a graphics processing unit? Why would that be valuable to the GIMPS project? I would think a CPU would be better. Thanks.
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Old 2016-01-25, 04:38   #2
kladner
 
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GPU=Graphic Processing Unit

Modern GPUs excel at calculation. In particular, in the GIMPS context, they are unbeatable at Trial Factoring compared to CPUs. There are also programs which perform LL testing, just as Prime95 does. They are faster at that than all but the most powerful CPUs. There are applications for both nVidia and AMD graphics processors.

If this seems odd, consider that the most powerful super computers these days use large numbers of high end GPGPUs** to achieve amazing throughput on complex tasks which include climate modeling and similarly enormous calculations. These include nVidia Tesla cards and AMD FirePro processors.

**General Purpose GPUs.
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Old 2016-01-25, 07:08   #3
LaurV
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Think about a CPU as a very proficient, very skilled engineer. Actually, think to modern CPUs as a team of such engineers, 2, 4, 8, etc, according with the numbers of cores the CPU has. This "team" can do a lot of intelligent work when they cooperate together. You can imagine they are the wizards in the world of warcraft.

Now, think about the GPU as a team of stupid middle-age peasants, like in the world of warcraft. Or an army of ants. Each peasant/ant can't do much, but they are A LOT! Modern GPUs have thousands of such peasants inside.

When it comes to hammering the iron, which team do you think will do more work?

Most of the people think to a GPU like some tool specially dedicated to manipulate images. Maybe it was like that in the beginning. Any image is composed of pixels, little colored dots on the screen, and no matter what "special effect" you want to give to that image, you only operate stupid modifications to those pixels, like adding them together or masking them by hiding them behind a stencil. So, the calculus is not complicate, at the end, but you have millions of such pixels (one image of 1000 times 1000 contains already a megapixel) and you have to operate all of them 60 times per second. Not exactly a task for a team of engineers. More like, an army of peasants would do the work much better and faster. The CPUs were quite slow at that task, it was a lot of boring work for them. Take a pixel, make it darker, take next one make it lighter, repeat a million times... Boring!

That is how GPU were born, take a thousand processors and put them to manipulate the pixels in the same time. But because the energy and physical space for such a team would be enormous, let's reduce their intelligence, making them stupider, but smaller, and more power efficient. Like take 2000 engineers, cut all their legs and one hand of each, and pack them in a box. They won't need much food, because they won't move much, etc... Nice image huh?

Of course, we would like to have a team of 2000 high qualified engineers inside of our rigs, it is not difficult to get them, they exists, but they are called "supercomputers" and they are only a hundred in the world... But if you have enough money, you can get one. And you will need a whole block of buildings to host one.

Till then, we are happy with armies of peasants, i.e. GPUs, which we can afford to buy, and we don't need a production hall to keep them. Those peasants inside a modern GPU are very stupid, but that is why (or "that is because"?) they are very small, so they can fit in the box, and are affordable. But there is an army of them. Meantime the things evolved there too: it is true that the peasants are still only able to do their silly work, and no more, but now they can apply that work not only to graphic pixels (which are just some bits in the memory, aren't they?) but to general data stored in the memory too. They are called "GPGPU", or "general purpose" GPUs. They are very good at doing very simple repetitive tasks. If you want to add one thousand pairs of numbers to get one thousand sums, one engineer will take a lot of time to do it. But 1000 peasants will do it immediately. Better use the engineers for more complicate tasks, that is why you pay so much money for their salaries...

If you want to move a very complicate machine between two buildings, then you call a team of 10 engineers. When you want to move few million bags of rice between two buildings, you better call a team of 2000 peasants!

Looking for primes is the same. To find a prime you must first eliminate all numbers which are not prime. Like for example, you will eliminate all even numbers, because they are divisible by 2. Then all numbers divisible by 3. Then all divisible by 5. This is called the "sieve of Eratosthenes" and you can google for it. The process is called "trial factoring" or TF. Because you first try to factor your numbers, and if you find a factor, then they are not prime (called "composite") and you don't need to test them for primality anymore.

This trial factoring involves dividing a lot of big numbers (the candidates for primality) to a lot of small prime numbers (their possible factors). What do you think this is a task for? Ten engineers, or 2000 workers?

This was just an example. Stick around and you will find more exciting things. Welcome to the project, by the way.

Last fiddled with by LaurV on 2016-01-25 at 07:30
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Old 2016-01-25, 11:31   #4
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Old 2016-01-25, 16:44   #5
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Truly outstanding explanation, LaurV!
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Old 2016-01-26, 00:28   #6
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is it possible to add a gpu to my current computer? I doubt it, but I thought I'd ask. I assume it would have to be on the motherboard?
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Old 2016-01-26, 05:27   #7
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Quote:
Originally Posted by jschwar313 View Post
is it possible to add a gpu to my current computer? I doubt it, but I thought I'd ask. I assume it would have to be on the motherboard?
Give us a rundown on your motherboard and setup, including power supply capacity, CPU, amount of RAM, OS, and the brand and model of computer, if applicable. You need to have a free 16x PCIe slot. However, if you are currently running your display from onboard graphics, and it is some brand-name machine, the power supply might not support a high-end GPU running flat out all the time. Enough power is critical for stability.

To answer your actual question, yes. A GPU is plugged into the motherboard. It will also require a particular sort of power supply connector(s).

Fill in the details, and people here will certainly give feedback, and options as they see them.

EDIT: All of the above was written assuming that you have a desktop machine. A laptop is a whole different situation which I cannot effectively address.

Last fiddled with by kladner on 2016-01-26 at 05:41
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Old 2016-01-27, 01:54   #8
jschwar313
 
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I have a Dell XPS 8300 with 8GB of RAM. I will attach some more detail to this message. I don't think it has power supply information in it. They were from some tests I found on the internet from Intel. Let me know what else you need. I'd also like to know about how much this will cost. Thanks so much.
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Old 2016-01-27, 02:21   #9
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You have and i7 2600, 3.4 Ghz. That is a very respectable CPU for Prime testing. It comes with onboard graphics, but it also has a PCIe x16 slot. One of the screen shots mentions the possibility of graphics adapters up to 225 w.

So yes, you should be able to put a GPU in that system as long as you choose something that stays within the power limits. The second screenshot came from the XPS8900 page, but the power supply is the same on the 8300.
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Old 2016-01-27, 02:54   #10
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Probably the best value for a GPU for that system is a 970.

http://www.geforce.com/hardware/desk...specifications

We like the ones that have a fan that exhausts outside the case.

http://www.evga.com/Products/Product...04G-P4-1972-KR

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Old 2016-01-27, 03:09   #11
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Quote:
Originally Posted by Xyzzy View Post
Probably the best value for a GPU for that system is a 970.

http://www.geforce.com/hardware/desk...specifications
What about the R9 Nano? Same performance per dollar and much better performance per watt for TF according to James' table.
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