To illustrate exactly how the new Radeon HD 4830 differs from the Radeon HD 4850 and HD 4870 that preceded it in terms of specifications, we've got a simple chart that outlines the main differences between the cards.
As you can see, the Radeon HD 4830 differs from its 4800 series counterparts only in its number of stream processors, texture units, and clock speeds. Two of the RV770 GPU's 10 SIMD arrays and associated texture units have been disabled, which results in a total of 640 active stream processors--down from 800 in the Radeon HD 4850. The Radeon HD 4830's core clock has also been lowered a bit, to 575MHz. The result is less compute performance and fillrate. Memory bandwidth is down as well, but that's only because of a clock speed reduction, as the Radeon HD 4830 has the same memory bus width. Another interesting aspect of the list above is max board power. AMD is rating the cards at a maximum of 110W, just like the 4850. Convention wisdom suggests power consumption would be lower, but AMD is being conservative here because they are binning more chips from a die and may need to goose the voltage on some of them to reach the desired specs.
There's nothing much new to see here physically. AMD's reference ATI Radeon HD 4830 looks exactly like a Radeon HD 4850. We were informed, however, that most board partners would be offering non-reference Radeon HD 4830s that use different PCBs, coolers, memory, etc. And that seems to be true as evidenced below...
The PowerColor Radeon HD 4830 is completely different from AMD's reference design. The card has a shorter PCB (by about an inch), custom dual-slot cooling, and a unique assortment of outputs. In lieu of a TV output and second DVI connector, this card sports an analog DB15 VGA connector and a DisplayPort. Also, remember that these cards support HDMI output with audio when used with the correct DVI-to-HDMI dongle.
The specifications on PowerColor's offering are identical to the reference design with a 575MHz core clock and 512MB of 900MHz GDDR3 memory. PowerColor's cooler, however, performed better. Whereas the reference card would peak with an approximate 82'C GPU temp under load, the PowerColor Radeon HD 4830 never broke 76'C. Both remained very quiet during testing.