ddr3 vs gddr3

[nemisi]

is there a performance difference between gddr3 and ddr3 and which one is better to go for ??

[ViperJohn]

is there a performance difference between gddr3 and ddr3 and which one is better to go for ??


The G stands for "Graphics". All DDR, DDR2, DDR3, DDR5 used on GFX cards is GDDRx...the G is just often dropped.

Viper

[largon]

Except that "GDDR2" on modern boards is really just ordinary DDR2, the same stuff used as system memory. The real GDDR2, which is totally different than normal DDR2 hasn't been manufactured in years now.

[Firestrider]

What is the main difference between the two? I know GDDR3 is used for graphics cards and DDR3 is used for main memory, but why can't say GDDR5 be used as main memory? Is there a difference in latency and bandwidth between GDDR3 and DDR3 when using the same bit-width bus?

[ViperJohn]

Except that "GDDR2" on modern boards is really just ordinary DDR2, the same stuff used as system memory. The real GDDR2, which is totally different than normal DDR2 hasn't been manufactured in years now.


That is absolutely incorrect. Standard DDR memory of any type would make a GFX card so slow
it would be useless. Samsung still has GDDR2 in mass production.

www.samsung.com/global/business/semiconductor/products/dram/Products_GraphicsMemory.html

Viper

[ViperJohn]

What is the main difference between the two? I know GDDR3 is used for graphics cards and DDR3 is used for main memory, but why can't say GDDR5 be used as main memory? Is there a difference in latency and bandwidth between GDDR3 and DDR3 when using the same bit-width bus?

An address of Video memory ram can be read and written to in the same clock cycle and and costs
considerably more the system memory. Roughly 1/2 the cost of a GFX card is the memory on it.

That ability is not needed for system memory where you have ultra fast cache memory in the CPU
itself. It is basically the way the memory is used and the information stored. System memory holds
mostly static data like code for of various files of the OS and programs you are running (.exe files,
.dll files, driver file, etc, etc) that doesn't change once loaded.

The data held in video memory is largely dynamic, volatile and is changing constantly as you move
around the scene of say a 3D 1st person shooter. It can hold relatively static data like the memory
map for say your windows desktop but once into a fast moving 3D type game the amount of data
movement and changes in a GFX cards memory is massive compared to system memory. Much of the
data held in GFX memory is used once then replaced with new data as what you are seeing on the
your display is constantly changing at your FPS rate.

This a gross over simplification but you get the idea.

Viper

[th3]

I looked at the data sheet for "Samsung gDDR2", looks like plain DDR2 RAM, that explains the lower case "g". Qimonda doesnt even bother to use the "g" in gDDR2 in their data sheets, it just says "DDR2".

http://www.samsung.com/global/system/business/semiconductor/product/2008/5/28/317674ds_k4n1g164qq_rev10.pdf

[ViperJohn]

I looked at the data sheet for "Samsung gDDR2", looks like plain DDR2 RAM, that explains the lower case "g". Qimonda doesnt even bother to use the "g" in gDDR2 in their data sheets, it just says "DDR2".

http://www.samsung.com/global/system/business/semiconductor/product/2008/5/28/317674ds_k4n1g164qq_rev10.pdf

It's not the same...not by a long shot.

Viper

[Firestrider]

Is it the memory chips or the memory bus that makes the card expensive? Like I know the GTX 280 has a 512-bit bus and is around $450 (which in my opinion is way overpriced for the performance) but it might be almost that much to manufacture. The 2900XT also had a 512-bit bus and it was really expensive too. The HD 4870 1GB with GDDR5 memory chips and a 256-bit bus has almost the memory bandwidth as the GTX 280 but is about $100 cheaper. The difference between the 4870 1GB and 512MB is only about $40, though.

[ViperJohn]

Is it the memory chips or the memory bus that makes the card expensive? Like I know the GTX 280 has a 512-bit bus and is around $450 (which in my opinion is way overpriced for the performance) but it might be almost that much to manufacture. The 2900XT also had a 512-bit bus and it was really expensive too. The HD 4870 1GB with GDDR5 memory chips and a 256-bit bus has almost the memory bandwidth as the GTX 280 but is about $100 cheaper. The difference between the 4870 1GB and 512MB is only about $40, though.

It is the chips themselves. The ability of Vram to be able to have memory addresses read and then written to in the same clock cycle at the speeds they operate at (at the time in history of primary manufacture and use) costs money.

GFX cards are also limited in real estate to plant memory chips on so they are typically using higher density chips to achieve a given memory size...at least on the high end cards that push the memory size envelope.

When you combine the Vram memory access ability, the chip density and the speed they are running it pushes the chip prices way up (again (at the time in history of primary manufacture and use).

GFX cards are roughly two years ahead of system memory on the type used too due to the operating speeds needed with the operating parameters as to accessing the chip data via reads/writes and the limited space on the cards. With System memory DDR2 is still common and DDR3 is just really starting to catch on. GFX cards on the other hand have long ago stopped using GDDR2 and GDDR3 is well on the way out...at least on the mid to high end cards. Using the current state of the art chip types (GDDR5 at this time) on the high end cards is also more expensive.

As an example DDR5 system memory is still a couple of years away and by that time high end GFX card will be probably be using GDDR7 (or what ever the chip makers choose to call it at the time.)

Using a wider memory bus is one way of extending the use time of lower bandwidth part like say GDDR3 with a 512bit wide bus (and tighter memory timings) versus GDDR5 with a 256bit wide bus (with the looser memory timings of GDDR5). The bandwidth can end up the same either way. It is just a different way to skin the same bandwidth needed cat.

Both NV and ATI balance the needed bandwidth at the time with the costs of getting it one way or another. They never put more memory bandwidth on a card than is actually needed for the target design at the time as that just runs costs up needlessly.

Viper

[largon]

It's not the same...not by a long shot.Modern "GDDR2" is the exact same DDR2 used as system memory, 16bit bandwidth is the only difference.
Google "K4N26323AE (http://www.google.fi/search?&q=K4N26323AE&)" (GDDR2 used on FX5700Ultras) and see it for yourself.

For example, "K4N51163QG" one of the modern "GDDR2" chips (= DDR2), is nothing like the actual, ancient GDDR2 like "K4N26323AE". The fact that Samsung (and many chip makers) dub the chips as "GDDR2" means nothing.

[ViperJohn]

Modern "GDDR2" is the exact same DDR2 used as system memory, 16bit bandwidth is the only difference.
Google "K4N26323AE (http://www.google.fi/search?&q=K4N26323AE&)" (GDDR2 used on FX5700Ultras) and see it for yourself.

For example, "K4N51163QG" one of the modern "GDDR2" chips (= DDR2), is nothing like the actual, ancient GDDR2 like "K4N26323AE". The fact that Samsung (and many chip makers) dub the chips as "GDDR2" means nothing.

Largon you should know better. While we are talking a positively ancient memory as far as GFX cards are concerned they were and probably still are not the same. The distinction between the two this late in the product(s) cycle may certainly be blurred now with the differences in technicals, production and use between the them melded together with product production consolidation over time. While the low end cards these days may very well use common DDR2 SDRAM (or it may be the other way around with DDR2 system memory using tweaked GDDR2 Vram chips) that doesn't make it the "exact same" GDDR2 GFX memory (Vram) that can have it's memory addresses read and written to in the same clock cycle. This would be especially true back in the beginning and main stream days of GDDR2 use on GFX cards.

Samsung DDR2 SDRAM (System Memory)
www.samsung.com/global/business/semiconductor/productList.do?fmly_id=108

Samsung GDDR2 (Graphics Vram)
www.samsung.com/global/business/semiconductor/productList.do?fmly_id=676

Viper