Novuake :
GDDR5 is modified DDR3 RAM.
The fundamental principles and structures between mainstream DRAM generations has been largely unchanged in the past 15+ years since the introduction of synchronous DRAM. Little more than die shrinks, voltage reductions, clock speed range increases, interface clock multiplication and relatively minor tweaks to the electrical protocol itself are the only things that separate modern DRAMs from their ancestors.
Even FBDIMM, RDRAM, XDRAM and other fancy memory types rely on the exact same internal structures as ancient DRAM types. The only difference between DDR3 and GDDR5 is they rip out the DDR3 front-end and replace it with GDDR5. Neither is 'based' on the other, they merely share the same fabrication process and ancient general structure.