features a slot-loading 2× speed Blu-ray Disc drive for games, Blu-ray movies, DVDs, and CDs. It was originally available with hard drives of 20 and 60 GB (20 GB model was not available in PAL regions) but various sizes up to 500 GB have been made available since then (see: model comparison). All PS3 models have user-upgradeable 2.5" SATA hard drives. PlayStation 3 uses the Cell microprocessor, designed by Sony, Toshiba and IBM, as its CPU, which is made up of one 3.2 GHz PowerPC-based "Power Processing Element" (PPE) and eight Synergistic Processing Elements (SPEs). To increase yields and reduce costs, the chip has 8 SPEs. After manufacture, every chip is tested and a defective SPE disconnected using laser trimming, leaving 7 SPEs. This means that otherwise discarded processors can be used, reducing costs and waste. 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 produce resolutions from 480i/576i SD up to 1080p HD. PlayStation 3 has 256 MB of XDR DRAM main memory and 256 MB of GDDR3 video memory for the RSX. Originally, Sony did not plan to include any GPU in the PlayStation 3, because they thought that the Cell could handle everything, but the developers, including the ICE team from Naughty Dog, demonstrated to Sony that without a dedicated GPU, the PlayStation 3 performance would not be sufficient, particularly in comparison to the Xbox 360. Sony henced added a GPU, the Nvidia RSX, at the final stage of the PlayStation 3 development. The system has Bluetooth 2.0 (with support for up to seven Bluetooth devices), Gigabit Ethernet, USB 2.0 and HDMI 1.4 built in. Wi-Fi networking is also built-in on all but the 20 GB models, while a flash card reader (compatible with Memory Stick, SD/MMC and CompactFlash/Microdrive media) is built-in on 60 GB and CECHExx 80 GB models. Models PlayStation 3 has been produced in various models: the original, the Slim, and the Super Slim. Successive models have added or removed various features, reduced the console's initial purchase price and weight, and increased storage capacity (with exceptions). Controllers and accessories Numerous accessories for the console have been developed. These accessories include the wireless Sixaxis and DualShock 3 controllers, the Logitech Driving Force GT, the Logitech Cordless Precision Controller, the BD Remote,