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Old 7th March, 2004, 10:04 PM
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GFX and PC RAM

Quick question - im sure this is easilly answered but am curious all the same. Based around 2 points and a question:

1) We have graphics cards that use 2.8ns ram
2) The best ram out their (winbond BH5) is 5ns ram

Why the heck arent we getting these ram chips stuck on memory that completely flies? Are the timings very different on the ram sticks or the PCB design for the access radically different to GFX ram?
Or am I being dumb and this is the kind of stuff used on the cas 3 high bandwidth stuff designed for P4`s?
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Old 8th March, 2004, 01:12 AM
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correct me if im wrong, but isnt this the case because manufacturing PC RAM with 2.8ns chips would be just too expensive for manufacturers to mass-produce?
btw: i believe the the bh5 chips arent the fastest, i use RAM with 4.5ns chips
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Old 8th March, 2004, 11:39 AM
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Two reasons: Cost and timing problems.

The high speed RAM is more expensive than slower RAM. It's also lower density, so you need more chips to acheive the same amount of memory. For example both Hynix and Samsung do 1Gbit DDR chips for standard RAM. They only do 256Mbit chips for Graphics RAM.

I haven't been able to find out any pricing however.

The second point is that as RAM gets faster, timing becomes more and more critical. In order to run very high speed RAM, you need to remove the sockets, as they add latency to the signals. This means soldering the RAM directly to the motherboard. That leads people with no way of upgrading/changing their RAM should they wish to do so!
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Last edited by Áedán; 8th March, 2004 at 11:47 AM.
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Old 8th March, 2004, 10:06 PM
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Quote:
Originally Posted by Áedán
Two reasons: Cost and timing problems.

The high speed RAM is more expensive than slower RAM. It's also lower density, so you need more chips to acheive the same amount of memory. For example both Hynix and Samsung do 1Gbit DDR chips for standard RAM. They only do 256Mbit chips for Graphics RAM.

I haven't been able to find out any pricing however.

The second point is that as RAM gets faster, timing becomes more and more critical. In order to run very high speed RAM, you need to remove the sockets, as they add latency to the signals. This means soldering the RAM directly to the motherboard. That leads people with no way of upgrading/changing their RAM should they wish to do so!
Hmmm... well... from my (admittedly sheep following) understanding bh-5 are the daddy?

Also agreed with both on the point of cost but we've seen with the silly prices some people can get for BH-5 based ram like the mush level 2, folks WILL pay big bucks to be at the very bleeding edge. Thats without talking about prommies, extreme/expensive mods etc.

In reply to aedan about the ram - its asking for trouble in certain areas but on the very top performance boards why not have chip holders attached directly to the board? Yes it mean that once you move outside the "window" of upgradability the board was designed for you have to buy a new board but this happens now - just not as often and again - for very top end - the market appears to be there

With the point about Ram sizes - i've not yet seen single chips over 128MB used in the home market either on graphics or system memory? 1 gig chips tend to be double sided PCB`s with 4 chips each side (1024) and graphics cards tend to be max of 8 chips also - 4 on each side (so would assume are using 64MB chips.)

Just a few ideas I been mulling over so thought Id throw to the floor
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Old 9th March, 2004, 12:35 AM
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With high speed RAM, you can't have any 'chip holders' - they add propagation delay which is critical. With high speed RAM, the margins are in the order of picoseconds. The net result is that the RAM has to be soldered directly to the board. That, in turn, means zero upgradability. Additionally, you're limited to the number of RAM chips in place, as each chip adds extra capacitance to the data and address lines.

In terms of RAM size, you're confusing bits and bytes. Memory chips are specified in bits, where as memory modules are specificed in bytes. Hence a 1GByte module with 8 chips on it provides 8192Gbits of storage. That means each chip is a 1Gbit chip.
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Old 9th March, 2004, 12:56 AM
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Quote:
Originally Posted by Áedán
With high speed RAM, you can't have any 'chip holders' - they add propagation delay which is critical. With high speed RAM, the margins are in the order of picoseconds. The net result is that the RAM has to be soldered directly to the board. That, in turn, means zero upgradability. Additionally, you're limited to the number of RAM chips in place, as each chip adds extra capacitance to the data and address lines.

In terms of RAM size, you're confusing bits and bytes. Memory chips are specified in bits, where as memory modules are specificed in bytes. Hence a 1GByte module with 8 chips on it provides 8192Gbits of storage. That means each chip is a 1Gbit chip.
Would this not even be possible if/when we move to a pin grid array packet for ram? I didnt say IC for "chip holder" as i know they wouldnt be up to the task, was speculating about some other way of mounting the chip that would make it upgradable to the end user.

Thanks for sorting out the confusion over ram chips - point taken on that read it as GByte and Mbyte
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Old 9th March, 2004, 05:46 AM
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The problem is that, as Aedan points out, ANY packaging technique that allows for easy removal of components by the end user also introduces an extra set of connections into the mix. Every connection you introduce into the circuit creates another reflection point for the signal, adds extra capacitance to the bus, and in general just causes a lot of headaches.

If people realized just how close to the ragged edge of disaster modern electronic systems routinely operate, they wouldn't use anything more sophisticated than a toaster.
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Old 9th March, 2004, 07:50 AM
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Quote:
Originally Posted by MercutioUK
Would this not even be possible if/when we move to a pin grid array packet for ram?
It doesn't matter what mounting system you use. You end up introducing delays from contact resistance and capacitance. Besides, RAM has already moved to FBGA to further reduce the problems of impedence change between track and packing. FBGA does a better job of this than PGA.

If I understand correctly, the difference between operation and disaster for DDR266 RAM is a tad over 200picoseconds (0.2nS). That's only DDR266 - how small does that get for DDR800?
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Old 9th March, 2004, 03:55 PM
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Dunno........the last time I looked really hard at RAM specs we were still using 1 megabit chips. LOL
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