DDR4 modules don't look different at a glance but there are some subtle differences. DDR4 RAM is not backwards compatible with DDR3 motherboards and vice versa. The notch has been moved to prevent accidental insertion of the wrong type of memory. Instead of 240 pins, each module features 288 pins.
In this regard, can you put a ddr5 graphics card on a ddr4 motherboard?
Yes! Graphics cards are cross compatible with the DDR2-DDR4 Motherboards. Long Answer: As long as your motherboard has a pci express slot you can fit any graphics card even if your motherboard supports DDR3 or DDR2 ram.
Can I use any graphics card in any motherboard?
Typically they will all be PCI Express, but for a graphics card you need a PCI Express x16 slot. There are three versions of this slot, but they're backwards compatible, so a modern PCI Express 3.0 graphics card will work in a motherboard with a PCI Express x16 2.0 slot. This motherboard has two PCI Express x16 slots.
What is the difference between gddr5 and ddr3?
A 2 GB GDDR5 card would beat a 4GB DDR3 card any given day. While DDR3 memory is more used for general computing, GDDR5 is dedicated to graphics performance. GDDR5 has better memory bandwidth and a significantly higher memory clock speed, so it is better to go with GT 755M.