Radeon HD 7950 only showing 1GB of graphics RAM Rather than 3GB

Hi. As the thread title says my MSI Radeon 7950 graphics card ought to have 3GB of memory. Using Catalyst Control Centre hardware information it states that the memory size is 3072MB however in the Display section of System Information it says the Adapter RAM is 1,073,741,824 bytes. CPUID CPU-Z also says that the graphics memory is 1024MB. Does anyone know why this might be?

My PC spec is:

Windows Ultimate 64Bit
Intel Core i7 3770K Processor Overclocked
Antec KÜHLER H2O 920 Liquid cooling system
Asus P8Z77-V LK Motherboard
32GB G.SKILL Trident-X DDR3-2400 MHz (PC3-19200) Memory
MSI Radeon HD 7950 3072MB Graphics Card
Corsair TX 850W V2 PSU
OCZ 256GB Vertex 4 SSD
2000GB 7200RPM Hard Disk - 6Gbps
Samsung Blu-Ray ROM / DVD-RW Combi Drive
Thermaltake Overseer XR-I Black Case

Many thanks.
Chris