Previous iMac with reduced frequency and low-cost graphic memory (VRAM), laptops with down-clocked GPU, premium price but low-cost parts. And performance lagging far-behind half-cost PC!

This time, it’s the Radeon HD 5670, that ATI specify for GDDR5 with 64GB/s bandwidth. Only GDDR5. Apple put GDDR3 on it to attain 32GB/s, diminishing performance on a 1.5X to 2X factor! That might be a 10$ or 20$ economy for Apple, 1% of the iMac, but a real performance loss for gamers and anyone using GPU, for OpenCL, CUDA, Photoshop CS5 Suite, …

Notice that the ATI Radeon HD 5750 of the Quad-Core 27″ iMac is in fact a HD 5850 Mobility, offering approximately same level of performance, but less bandwidth (as usual).

Steve, sometime you are really cheap!

PS: Preceding iMac 27″ Core i5 Quad-Core had ATI Radeon HD 4850 with GDDR3, but offering 64GB/s bandwidth, having 256bits bus instead the 128bits bus of the HD 5670.

On the GPU side, as nVidia seems to be unable to launch new GPU since 2007 and G80, GeForce 8800, for the gamer or fot he mobility market, just trying to hide evolutions of this old chip with marketing rebranding, and Apple choose ATI GPU for the iMac, it seems nVidia wont be the next generation MacBook Pro choice.

Obviously, the new Radeon HD 5830 Mobility seems to be the best GPU for MacBook Pro, with 24W TDP, compatible with actual design and cooling fan, it offers up to 800 Gflops raw processing power for OpenCL and 3D, and 25.6GB/s memory bandwidth, it might be a great choice for OpenCL but a bad one for 3D.

Effectively 3D performance will be just a little better than last-generation 8600M GT or actual 9600M GT (nVidia rebranded the 8600M GT to hide it’s inability to create new chips) with same 25Gb/s memory bandwidth, but will shine on the raw processing side for OpenCL software, such as video encoding, photo processing, antivirus, compression, encryption, raid management… In OpenCL the Radeon HD 5830 Mobility could deliver up to 6.5X the raw processing power of actual MacBook Pro GPU while keeping same TDP.

Radeon HD 5750 Mobility might be a better choice for OpenCL and games, with “only” 500 Giglaflops of raw processing power because of it’s memory bandwith of 51 GB/s, that will help for both games and applications. This will be my GPU of choice, even if the name seems to imply that it is less performing than the 5830!

I suspect there will be two choice, as in the iMac lineup, with probably the HD 5650 Mobility as entry-level GPU, with same raw processing power but only 25.6GB/s GDDR3 memory.

My guess will be Apple offered Radeon HD 5650 Mobility with 512MB DDR3 or GDDR3 on all MacBook Pro and HD 5830 with 1GB GDDR3 on 17″ or built-to-order configuration. But alas we won’t see the really interesting HD 5770 on MacBook Pro.

PS: with same TDP, nVidia offers the GT 240M, that is marginally faster than the 8600M GT and the n-th evolution of GeForce 8xxx G80 chip, with only 25GB/s memory bandwidth (same as GeForce 8600M GT), and 178 Gflops, so Radeon HD 5770 offers 2.5X memory bandwidth and 3X raw processing power, nVidia is totally out of the mobility market!