Graphics RAM for Beginners

This is a little guide for an often asked question.

Theres actually 2 kinds of GDDR3 implemented in the industry.

Samsung kindly has provided some of the best documentation available which highlights the differences quite clearly.
http://www.bdtic.com/DataSheet/SAMSUNG/K4J52324KI.pdf
http://www.samsung.com/global/business/semiconductor/file/product/ds_k4w2g1646e_rev101-0.pdf
http://www.samsung.com/global/business/semiconductor/file/product/graphic_product_guide_nov_12-0.pdf

For starters, I'm going with Samsung's internal terminology to save the confusion.

gDDR3=DDR3 SDRAM that has been optimized for high bandwidth graphics operation. This means that the latency is extremely high compared to the variety used as system RAM in order to hit those high frequencies without resorting to extreme binning.
GDDR3=GDDR3 SGRAM which is based on DDR2 signalling technology. Basically, completely different technology to the gDDR3.
GDDR5=GDDR5 SGRAM which is based on DDR3 technology that has further signalling improvements that allows the data to be quad pumped as opposed to double pumped. This basically doubles throughput at the same clockspeeds as DDR3.

Within the scope of this discussion, I'll omit the specifics regarding GDDR5 as it is quite complex.

gDDR3 vs GDDR3

Differences

1. Packaging: GDDR3 comes in a 136Pin BGA whereas gDDR3 uses the 96pin BGA. The immediate difference is that they are not pin compatible
2. Operating Voltage/Power: GDDR3 operates at 1.8V while gDDR3 operates at 1.5V with the latest units capable of 1.35V. This directly means that GDDR3 uses more power and generates more heat. GDDR3 is also rated for a 73 degrees Tjunction while gDDR3 tops out at 38.9 degrees
3. Performance: I've spent years trying to deciper the documentation but I'm no closer to being able to judge the content. As far as I can tell, GDDR3 is capable of higher speed operation at a lower latency than gDDR3
4. Density: gDDR3 is available in much higher density packages than GDDR3 due to better die area efficiency.

So why is gDDR3 now so popular despite being slower? It uses far less power and is much denser. This means, that for OEMs, it is cheaper to utilize larger amounts of VRAM for GPUs with little worry of heat generation/power usage (albeit the gDDR3 units are more fragile to heat) for a nominal drop in performance. GDDR3 hasn't really been used since the GeForce GTX285 went EOL.

If someone is more knowledgeable and is able to decipher Samsung's schematics, please contribute.

 

What you are referring to as "gDDR3" is commonly simply referred to as "DDR3," is it not? I've never heard of the "gDDR3" monicker applied to it before though.

 

Samsung's terminology on their spec sheet, it's commonly known as GDDR3 though this is slightly ambiguous as it can refer to the DDR3 or DDR2 technologies. Hence I'm assuming the small g to denote DDR3 that is bandwidth optimized.

 

That would be my guess as well, on most spec sheets, you either see GDDR5 or DDR3, in the older days you either saw GDDR3 or DDR2. The way Samsung and laptop OEMs differenciate vRAM may be different.