Bubun Karmakar :
I do really want to know the difference between a ddr3 GPU and ddr5 GPU.
Both have to do with memory bandwidths. The short answer is that GDDR5 results in faster memory bandwidth than DDR3.
The longer answer is that GDDR5 is the more recent type of double data ram, the "G" standing for "graphics", and is just for graphics cards. I can't remember exactly how much, but I think it's roughly twice as fast as DDR3. Don't quote me on that part, but what I do know is how this all plays into memory bandwidth for your video memory.
The formula for memory bandwidth is given by the following: Memory Clock * Bus Width * DDR multiplier. This is how fast a graphics card can access and exchange information with its pool of video memory. The memory clock is seen on most graphics cards technical info and can be equated to a car's speed limit on a highway. The bus width is also see on graphics cards and you'll usually see them as something like "128 bit" or "256 bit" graphics cards. This is the number of information channels that data can go through between a GPU and it's VRAM so it can be equated as the number of lanes on a highway. Lastly there's the DDR3 or GDDR5, which I'd say can be equated to the interval between when the next car in a lanecan travel. For example lets pretend that DDR3 only lets 1 car into each lane every 5 seconds while GDDR5 allows 1 car through each lane every 2.5 seconds. Clearly GDDR5 would allow more cars through in the end. A rough analogy, but it still works. Anyway, these all factor in to produce your memory bandwidth.
Memory bandwidth is important to ensuring that your graphics card is able to make use of its VRAM. For example, if everything in 2 graphics cards are the same except for the VRAM capacity and type, which would be better? Well if one was 1 GB of GDDR5, while the other was 2 GB of DDR3, the 1 GB of GDDR5 would be better because it'd be able to make more efficient use of its pool of memory. Similarly, it can get complex if you're looking at 2 GPU's and one has 1 GB of GDDR5 but with a 200 MHz memory clock and a 128 bit bus width, but the other has 1 GB of DDR3 but with a 400 MHz memory clock and a 256 bus width. In that case, the DDR3 would win.