stacking ram chips

[STEvil]

Ok, does anyone know how this works?

I remember a link on [H] back about oh... 4 months or more.. about corsair or maybe crucial releasing DDR DIMMS that had stacked ram chips to reach the correct density of 2gb or something..

My question is, if I took a video card with say 32mb of SDRAM and stacked a second set of (identical) chips on top of the first set would it become 64mb? Or am I understanding something wrong...?

If someone says "Yes, you are right, this is a go!" then i've got a project to do while the xabre 200 contest is rolling.. 8-)

[Banana_Boy]

wouldnt the card have to ave some type of coding to access the ram though?

[Soulburner]

Yup in the BIOS. But that can be arranged....

[STEvil]

Good to know.. where do I get my bios modified?? I dont want to give away what i'm doing right off the bat.. 8-)

[Holst]

It might work, but geting the card to use the extra may be impossible.

[Holst]

Im VERY glad to hear people thinking up stuff like this, this is exactly what the OC compo is all about trying stuff that (asfar as im aware) has never been done before.

[uwackme]

You could stack chips... and hold the top chip's CS (chip select) pin out in the air. The problem is some additional chip needs to decide based on address which of the two chips to access. Ex: for the 1st chip access to address's 0-32Mbytes generates it's chip select, but access to 32+1-64Mbytes instead chipselects the other chips.

On 512M sticks, this is EXACTLY what is going on. 2 banks of 256M of ram are on one PCboard, the stick specification has 2 banks allowed, and the northbridge has the signal to address which bank on the stick to access. Stacking chips you'd need an onboard little logic chip that looks at the MSBit (most significant bit) of the address to that bank on the stick and chooses to access bankTOP or bankBOTTOM of your little improvised stack.
Of course the time needed by the circuit to do that MUST be fast enough not to delay the ram access and data delivery.

This is at the heart of why adding 4 512M sticks to a canterwood for 2G of ram forces you to drop ram riming back...too much loading and bank select time to run at the same tight timings that only ONE stick(w/one bank) will be able to achieve.

So you only need 8 of the individual DDR chips on a stick to make 256M (the chips are 8Mx8bit chips...8x8bits = 64bit bus).

The next generation chips...will be 64Mbit and only 8 chips needed for 512M.

Also adding the additional chips again adds to the signal loading (think virtual resistor/capacitor/inductor network per pin) which at super high speeds like this is REALLY critical and has a huge affect on how fast you will be able to push things.

Effectively, the 1GIG sticks do on the PCboard the exact thing your chip piggyback would do....if you wrote out the schematic diagram... to the 512M stick design.

besides, soldering a bazilion little TSOP pins by hand....forget it you'd roast the chips long before you could finish soldering.

[wimpie007]

hmmzz...
Now I know why this place is called xtremesystems... :eek: :slobber:

[Vlad Draculea]

you can solder them but i am not going to explain how, instead i preffer spamming, good luck with the proyect

[STEvil]

I got hold of the item I am thinking of modifying today, and discovered one slight issue.

Card 1 has Toshiba 6ns chips, Card 2 has Hyundai 6ns chips... doh.

Being that I doing think its worth trying to stack the two different types of ram, i'll just fix the better of the two cards (a set of 3dfx Voodoo 5 5500's). heh... 8-)

Anyone with some volt mod skills have one handy? I was thinking of putting my 86 watt pelt on the faster card and vmodding it to try for 220mhz+... but I would need to figure out how to run more voltage to the ram, as my 3dfx V3 3000 topped at ~225mhz with no mods...

[KnightElite]

I can tell you right now: it won't work. All it will accomplish is that you will have duplicates of all your data stored away.

The idea itself is feasible, the problem is that you need different control information going to the different chips. All the chips on the card have the same data and address lines going to them, but then there are additional address lines to determine which chip will be accessed. This is done via external (to the chips) hardware, usually a demultiplexer, which then activates the appropriate memory chip when data is to be written/read to it. So stacking two chips with all the same inputs/outputs would do nothing, and unless the video card can handle addressing more memory than it has, it would be impossible to do (even if it can, it would be really hard).

EDIT: Read the whole thread, uwackme summed it up pretty good. You would have to leave the chip select pins hanging, and then somehow tie them into the BIOS chip so that it new to address teh new chips as well.

[autoexec]

so, if you found that a program you were using did not need all of the ram, you could take some off to lower the timming?

[Nookie420]

Originally posted by wimpie007
hmmzz...
Now I know why this place is called xtremesystems... :eek: :slobber:

I'll second that.

stacking seems really complicated. why not try swapping say 16MB chips out for 32MB chips and editing the bios accordingly(example)

[STEvil]

gotta find the chips.