ATi HyperMemory = nVidia TurboCache
They're pretty much the same technology; the name only depends on the company. The technology uses system memory for the GPU as a budget substitute to onboard physical memory for the GPU.http://www.newegg.com/Product/Product.asp?Item=N82E16814161006
HIS Radeon X1300 512MB
The 128MB indicates how much physical memory there is on the video card. But, the card supports 512MB - that's where HM/TC kicks in. The technology allocates 384MB of system memory (Your DDR/DDR2) to account for the full 512MB supported by the card.