4650/4670: Basic Specs
We’ve talked about some of RV730's specifications already, but it’s important to pause for a moment, pull back, and get some perspective. The graphics market moves so quickly that it’s easy to be fooled by numbers. For instance, the HD 4670 has a raw GFLOPS (billions of floating-point operations per second) rate of 480 while the new HD 5870 measures out at 2,720 GFLOPS. So you might assume that the 4670 has only 15% to 20% of the 5870's performance and thus only 15% to 20% of the 5870's total value. This would be misleading and erroneous.
For sure, if your sole purpose is to perform floating-point-intensive apps or keep looping 3DMark tests, then yes, the 4670 will be a small fraction of the today’s flagship parts. On the other hand, the 4670 is less than 20% of the 5870's price, so, from a benchmark perspective, you’re getting what you’re paying for. However, mainstream PCs are rarely ever tied to a single application. We use them for some gaming, sure, but also wide range of other tasks. It’s with these other tasks that we inevitably circle back to the Ford Focus vs. the Ferrari analogy. When you’re stuck with driving 25 MPH in the city, does it really matter which car you drive when all you care about is doing the task of getting from here to there? Of course not. A 4650 will deliver the same Web, Office, and MP3 playback experiences as a 5870 regardless of the price difference. So know the specs for what they mean, but take them in perspective.
That said, let’s throw out some numbers. As mentioned before, RV730 is based on a 55 nm fab process and a PCIe 2.0 interface, although a handful of cards placed the chips on an AGP 8X bus. Both the 4650 and 4670 can be paired with either 512MB or 1GB of memory, although exactly what kind of memory is one of the two ways in which these GPUs significantly differ. The 4650 can use either DDR2 or GDDR3 clocked at up to 700 MHz while the 4670 can use DDR2, DDR3, GDDR3, or GDDR4 clocked at up to 1100 MHz. Ultimately, this all translates into a memory bandwidth advantage of up to 57% for the 4670, although, once again, how much real life advantage you see will depend on how heavily your applications lean on video memory.
The other difference between these two chips is their core clock speeds. The HD 4650 runs at 600 MHz and the 4670 jogs a fair clip faster at 750 MHz. This difference is a key factor in the 4650 sporting a thermal design power (TDP) rating of 48W while the 4670 bumps up to 59W. An 11 watt difference may not sound like much, but if you’re upgrading a system with a fairly small power supply, 11W can be the difference between smooth sailing and random system resets.