The two USB ports on the front have been updated to the newer USB 3.1 standard and have a larger gap between them, and the optical audio port was removed. This model also features support for USB 3.1, Bluetooth 4.0 and 5.0 GHz Wi-Fi. It was released on September 15, 2016, with a 500 GB model at the same price as the original version of the PlayStation 4. On April 18, 2017, Sony announced that it had replaced this base model with a 1 TB version at the same MSRP. PlayStation 4 Pro (codenamed Neo, model number CUH-7000) was announced on September 7, 2016, and launched worldwide on November 10, 2016. It is an upgraded version of the PlayStation 4 with improved hardware to enable 4K rendering and improved PlayStation VR performance, including an upgraded GPU with 4.2 teraflops of processing power and hardware support for checkerboard rendering, and a higher CPU clock. As with PS4 "Slim", this model also features support for USB 3.1, Bluetooth 4.0 and 5.0 GHz Wi-Fi. The PS4 Pro also includes 1 GB of DDR3 memory that is used to swap out non-gaming applications that run in the background, allowing games to utilize an additional 512 MB of the console's GDDR5 memory. Although capable of streaming 4K video, the PS4 Pro does not support Ultra HD Blu-ray. Games marketed by Sony as "PS4 Pro Enhanced" have specific optimizations when played on this model, such as 4K resolution graphics and/or higher performance. For games not specifically optimized, an option known as "Boost Mode" was added on system software 4.5, which can be enabled to force higher CPU and GPU clock rates on existing games to possibly improve performance. Rendering games at 4K resolution is achieved through various rendering techniques and hardware features; PlayStation technical chief Mark Cerny explained that Sony could not "brute force" 4K without compromising form factor and cost, so the console was designed to support "streamlined rendering techniques" using custom hardware, "best-in-breed temporal and spatial anti-aliasing algorithms", and "many new features from the AMD Polaris architecture as well as several even beyond it". The most prominent technique used is checkerboard rendering, wherein the console only renders portions of a scene using a checkerboard pattern, and then uses algorithms to fill in the non-rendered segments.