Acer Aspire 5673 x1600

Pretty much the same issues with the 5672
http://www.notebookforums.com/thread155801.html

Underclocked x1600, and there is only 128 MB dedicated memory.
What scores do you get from 3DMark?

No solution as of yet, I doubt there will be unless we can somehow unlock the memory clocks.

The X1600 HM (HyperMemory) models have a 64 bit memory bus , where the X1600 models with dedicate memory only have a 128 bit memory bus.
In 5672 the X1600 HM is also underclocked, since it replaced the X1400 which was first used in the 5672 series, to match the heat levels of the X1400.

The mfgs tend to use lower buswidth with cheaper memory, all HyperMemory models X1300,X1400,X1600 have a 64 bit memory bus.
The memory bus is responsible for the communication between the Core (gpu) and the video ram of the gxf card. Having a low memory bus means the core cannot be fed enough resulting in a lower bandwith, even if the core runs at high speeds.

HyperMemory dynamically allocates memory when needed, so you ll reach the 512 memory buffer mostly when playing games. That explains the 136 mb 3dmark states. Even when the 512 RAM are used by your card dont except much difference since the 384 are out of your system's ram which runs at lower frequencies than then onboard video ram. Again the limited memory bus cannot take fully advantage of the larger memory buffer.

There are various tools to overclocked the card but the 64 bit memory bus is always going to be the bottleneck.

In my opinion HyperMemory is just a commercial tool rather than a performance boost, as it gives the right to vendors to 'lie' about the actual decidated memory of the card, since in most cases they state the sum (dedicated + shared)