i would've answered right away when you asked this, but i had to tie my shoelaces.
RAM memory is also used on video cards to make the video memory circuit. Until recently the video memory used the exact same technology as the system RAM memory that is installed on the motherboard. High-end video cards, however, needed memory chips faster than the ones used on the PC. So the manufacturers decided to go for DDR2 and DDR3 technologies.
DDR2 and DDR3 memories used on video card have different characteristics than the DDR2 and DDR3 memories used on the PC especially the voltage. Thats the reason they are called GDDR2 and GDDR3 (the G comes from Graphics).
DDR works at 2.5 V, DDR2 works at 1.8 V. This leads to a lower power consumption and less heat.
GDDR2 memories continue to work at 2.5 V. Since they run at higher clock rates compared to DDR memories, they generate more heat. This is the reason why only a few video cards used GDDR2 memories only GeForce FX 5700 Ultra and GeForce FX 5800 Ultra used this kind of memory. Shortly after GeForce FX 5700 Ultra was released many video card manufacturers released a GeForce FX 5700 Ultra using GDDR3 memories, maybe to lower the heat and power consumption effects.
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