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Built in RAM and Nothbridge Chips

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February 9, 2011 2:27:07 PM

I have been asking myself this question for a few years now and for the life of me I can’t come up with an answer. Why don't CPU's contain the memory and Northbridge chips inside the processor. After all they have Built in cache memory built in why not RAM. When you look at a Mainboard usually the traces go directly from the processor to the Northbridge and memory without any resistors or anything in the way. The chips themselves are made the same way as the processor. so why not simplify the whole thing and combine everything on one chip? While you’re at it add in a GPU and Southbridge and some SSD memory any you will have an entire computer on a chip. That would save a whole lot of space and with today’s cooling technology it would be feasible to keep the whole thing cool with a peltier or liquid/radiator setup. is it a marketing thing are they making more money selling the chips separately or is it just impossible to do.
Just my .02
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a c 128 } Memory
February 9, 2011 3:27:19 PM

Maybe they will someday. Intel finally put the graphics on the cpu die; that took several years until the size of the circuitry got small enough to have room for the graphics.
February 9, 2011 3:46:30 PM

Die space is valuable, attempting to fit it on sacrifices speed/efficiency of the CPU. You have to understand that they only integrate what improves performance.

So this means that with current technology having these items separate is more efficient than what we would be able to create with everything integrated. So having a CPU with a large amount of transistor space, large amounts of cache and higher clock rates is better than integrating the northbridge on it.

Also it is impossible to fit a reasonable amount of memory of the die, such as 512MB.
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February 9, 2011 3:49:32 PM

Today's CPUs do have the traditional "Northbridge" functionality built in.

Back in the day, the Northbridge chip had a RAM controller, graphics controller (some had the GPU itself, most had only the graphics control circuitry), CPU interface, and Southbridge interface built in. All of that is now built into the CPU (the most recent generations of Intel and AMD chips anyway). Only the Southbridge is a separate chip.

And yes, CPUs have a few (4-12 or so) megabytes of memory built in, but imagine the size needed for 1,024 megabytes (the average amount of graphics memory) or 4,096 megabytes (the average amount of RAM nowadays). Not really feasible for a while yet. Maybe within our lifetimes.
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February 9, 2011 3:54:42 PM

For most systems you dont really want to put everything on a single chip, it removes all modularity and forces you to produce a much wider variety of chips. If you put the memory on the CPU and then start running memory intensive programs, how are you going to add more memory to boost performance? You cannot unless you buy another CPU with more built in memory.

They sort of already added the memory to the CPU though, with L2 and L3 cache the size of old systems main memory so it has already been done, there is just always going to be a larger layer outside to reduce complexity of the chip, since bigger chips with more components are more likely to have a defect and that will cost you more.
February 9, 2011 4:21:12 PM

o1die said:
Maybe they will someday. Intel finally put the graphics on the cpu die; that took several years until the size of the circuitry got small enough to have room for the graphics.

they seem to have enough room to have 6 processor cores on a single chip why not a gig or 2 of RAM
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February 9, 2011 4:32:25 PM

Look at this image of the Sandy Bridge CPU:

Look at the size of the Shared L3 Cache section. That's only eight megabytes of RAM. A CPU with "a gig or 2 of RAM" would be absolutely HUGE -- four, five, six inches square or larger. They have problems with yields with the super-small CPUs now. Something that big would be impossible to produce in quantity with today's methods. Can you imagine cooling that beast? And what if some part of it fails?

Keeping things separate is better.
February 9, 2011 4:51:32 PM

Leaps-from-Shadows said:
Look at this image of the Sandy Bridge CPU: http://media.bestofmicro.com/sandy-bridge-core-i7-2600k-p67,8-4-275044-13.jpg

Look at the size of the Shared L3 Cache section. That's only eight megabytes of RAM. A CPU with "a gig or 2 of RAM" would be absolutely HUGE -- four, five, six inches square or larger. They have problems with yields with the super-small CPUs now. Something that big would be impossible to produce in quantity with today's methods. Can you imagine cooling that beast? And what if some part of it fails?

Keeping things separate is better.


Best answer so far...
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February 9, 2011 4:58:20 PM

hacker255 said:
was digging around on the internet and i came across a dual core ARM based processor with an integrated LCD controller and small amount of ram. it is only a matter of time before we see some awesome Computer on a chip portable devices.

http://ics.nxp.com/products/lpc4000/datasheet/lpc4310.l...


The memory on the chip that they are talking about is the cache, SRAM is almost always cache, its faster than DRAM but also significantly more expensive, when memory sizes are listed in kB its always cache. Most chips these days have wayyyy more cache than that, especially if you include L3 cache.

As for the integrated LCD controller, we already have them, they are in the i3's and i5's that have the GPU on the die already, the ARM just refers to it as an LCD controller because its designed for tiny devices that would combine the functionality of the LCD controller and the GPU into one chip because the screen isnt going to be changing often.
February 9, 2011 5:58:15 PM

i agree when stuff breaks having seperate replaceable parts is better. but think of the possibilities of a computer that fits on a chip.
the new sandy bridge 32nm architecture is amazing and it is being revised to handle up to 8 cores see link.

http://blog.trentontechnology.com/?Tag=Intel%20Sandy%20...

samsung has released info on their new ddr3 memory using 50nm technology (currently the smallest for ddr3 ram) the chips are 10mmx10mm including their ceramic coating. you only need 8 of them to make 1GB of ram.
http://www.samsung.com/global/business/semiconductor/su...

if the coating was removed the actual silicon chip would be a bit smaller. and if you can make them with 32nm technology theroedically each chip could shrink to under 6.4 mm lay them out in a 3x3 grid which = 9 chips total the cpu in the middle you come up with a package that is 19.2mm under 1"x1"

the technology is almost there

!