What's New About GDDR-3?
The list of differences between GDDR-3 and GDDR-1 memory is remarkably short. Basically, where GDDR-1 modules required 2.5V, the newer GDDR-3 chips use 1.8V (Micron) or 1.9V (Samsung). Also, the GDDR-3 specification calls for an on-die termination. Both of these improvements allow the chips to be run at much higher frequencies. Samsung demonstrated the modules with the highest frequency to date, running at no less than 800 MHz (1600 MHz DDR). In the future, expect to see chips with even higher clock speeds. The newer technology has one disadvantage compared to GDDR-1, namely much higher CAS latencies (CAS read latency). In practice, this means that GDDR-1 modules will be slightly faster than GDDR-3 chips at the same clock speed. However, this drawback is easily outweighed by the higher frequencies at which the chips can operate.
Although memory makers Hynix and Samsung list 256 Mbit GDDR-1 modules rated at 700 MHz and 800 MHz on their product pages, the fastest GDDR-1 modules available in appreciable quantities run at 500 MHz. Producing GDDR-1 memory that will operate at such high speeds is difficult, however, which is reflected in the almost prohibitively high prices of these modules. GDDR-3 modules currently produced by Samsung and Micron, on the other hand, only start at 500 MHz.
| Modules | Type | Voltage VDD,VDDQ | Frequency Range | Read Latency |
|---|---|---|---|---|
| 128M bit | GDDR-1 | 2.5V, 2.5V | 183-500 (800)MHz* | 3,4,5 |
| 256M bit | GDDR-1 | 2.5V, 2.5V | 183-500 (800)MHz* | 3,4,5 |
| 256M bit | GDDR-2 | 2.5V, 1.8V | 400-500 MHz | 5,6,7 |
| 256M bit | GDDR-3 | 1.8V, 1.8V | 500-800 MHz | 5,6,7,8,9 |
For the most part, GDDR-3 shares the same characteristics of the rather unsuccessful GDDR-2 specification. However, the strobes (impulse-scheme) and the receiver type were changed.
| Modules | GDDR-2 | GDDR-3 |
|---|---|---|
| Strobe Receiver Type | Bi-directional & Differential(DQS, /DQS)Push Pull | Uni Directional & Single-ended(RDQS,WDQS)Pseudo Open-Drain |
The only graphics cards known to use GDDR-2 memory were/ are the 256 MB version of ATi's Radeon 9800 Pro, NVIDIA's GeForce FX5800 Ultra and the aforementioned GeForce FX5700 Ultra. In practice, the greatest problem with this memory type was the high heat dissipation associated with it. Thanks to the lower VDDQ voltage of only 1.8V, GDDR-3 promises to solve these temperature-related problems - at least for the slower chips. Nonetheless, even these modules will require at least a passive heatsink.
You can find more information on GDDR-3 memory on the Hynix's and Samsung's websites:
- Samsung - GDDR-2 memory modules
- Samsung - GDD3 memory modules
- Samsung - Key differences between GDDR-2 and GDDR-3
- Micron - GDDR-3 memory modules
- Micron - GDDR-3 technical Notes
