What is Cuda 5.1 Graphic card drivers

hello please i need help.
i bought a Lenovo G50 and due to some problems i had, i formatted the system and reinstall a Windows 8.1 system and it is showing (4.96Gb ram usable) out of the 6 Gb of ram i have. Please i need explanation on that.
Also running adobe after effects , it is showing me , i need a CUDA 5.1 card drivers which i got an AMD A8 in my laptop. Please need explanation on all those stuffs.
i even downloaded the drivers but still not changing…
thank you.

Lenovo is selling G50 models without any nVidia graphics chip. On these models, you cannot run anything that relies on CUDA.

Some chipsets use part of the address space as a “window” to map PCI, AGP or PCIe card memory, such as graphics cards. If that address space isn’t automatically remapped to some other location (some lowcost chipsets simply cannot do this), the corresponding section of RAM will be lost. That seems to be the case on your system.