Firing Squad writes: "Despite offering the potential of higher clock speeds while consuming less voltage than previous memory types, GDDR4 graphics memory never really took off. ATI was first to adopt the technology into a shipping product: integrating GDDR4 for use on their Radeon 3870 GPU, but despite its blazing 1.125GHz clock speed, the memory latency was just too high in comparison to GDDR3 memory. GDDR4 was also pricier than GDDR3.
Considering all this, ATI opted to revert back to more conventional 900MHz GDDR3 memory for their dual GPU Radeon 3870 X2. ATI hasn't integrated GDDR4 on any of their GPUs since the Radeon 3870, and NVIDIA has passed on the technology altogether.
Now GDDR4 graphics memory is back, with Sapphire integrating the memory into their latest Radeon 4670 card."