Last week I posted about the rumors that all Radeon RX 480 4GB cards that are shipping right now actually have 8GB GDDR5 memory onboard. Word on the street is that AMD was unable to find enough 0.5GB GDDR5 memory chips with the desired 8Gbps memory clockspeed, so they decided to equip the cards with eight 1GB GDDR5 memory chips and locked the maximum addressable memory amount to 4GB.
TechPowerUp investigated this rumor and bought a Sapphire Radeon RX 480 4GB memory card from German webshop Alternate. The site used ATIFlash 2.74 to extract the BIOS of a 8GB card and transferred this BIOS onto the 4GB card. The result is as expected, the BIOS mod unlocks the full 8GB and the card performs on-par with a "real" 8GB card.
If you're an enthusiast, it's a relatively easy way to unlock a bit of extra performance out of the $199 card, effectively saving you $40. Unfortunately, the only way to figure out if you can upgrade the card is to disassemble the cooler, which will break some warranty seals. It's unknown which 4GB cards have 8GB memory onboard and it's expected that future batches will have the correct memory amount.
The 8 GB control and the modified 4 GB to 8 GB card performed on-par with each other. The 8 GB control card produced 24.6 fps, the 4 GB to 8 GB modified card produced 24.7 fps. The 4 GB card with its original retail BIOS produced 23.3 fps. To make sure that each GPU runs at a predictable GPU frequency (usually thermal and power limit reduces clocks), we've set both fan and power target to maximum, which results in a constant frequency of 1266 MHz on both cards.