The PlayStation 3 uses the Sony, Toshiba, IBM-designed Cell microprocessor as its CPU, which is made up of one 3.2 GHz PowerPC-based "Power Processing Element" (PPE) and eight Synergistic Processing Elements (SPEs). The eighth SPE is disabled to improve chip yields. Only six of the seven SPEs are accessible to developers as the seventh SPE is reserved by the console's operating system. Graphics processing is handled by the NVIDIA RSX 'Reality Synthesizer', which can output resolutions from 480i/576i SD up to 1080p HD. The PlayStation 3 has 256 MB of XDR DRAM main memory and 256 MB of GDDR3 video memory for the RSX.