The Sega Dreamcast was a good-looking console, the last console from Sega and one that introduced online gaming to a generation. This project, Dreamcast One, detailed by poster Temujin 123 on the Computerbase forums, takes a cutting tool to that beautiful casing and bores it out to fit a mini gaming PC inside. And it's a brilliant piece of work.
Inside the Dreamcast's 7.48 in × 7.71 in × 2.97 inches (190 mm × 195.8 mm × 75.5 mm) case Temujin 123 has managed to fit an AMD Ryzen 5 Pro 4650G, 16GB of DDR4-3200, and three SSDs via the judicious use of a Dremel. Choosing the AMD 4650G APU rather than a separate GPU for the PC is a smart move given the limited space, but Temujin 123 has managed to fit in the DVD-RAM drive from an old laptop. Cooling comes courtesy of a Noctua NH-L9a-AM4, there’s a Wi-Fi 5 card rather than a 33K modem, and the four controller ports now sport a USB upgrade.
The Dreamcast was already a mini gaming PC which ran a Hitachi SH-4 32-bit RISC processor, 26MB of various RAM types, and PowerVR2 GPU, it pioneered the use of off-the-shelf components for console building. Its Windows CE operating system (with a DirectX API that made porting PC games easy) and built-in modem made it very PC-like for the time, as did the keyboard and mouse peripherals.
Check out the forum thread for insights into how he did it, and a lot of pictures.