Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. The XS1-G4 is a processor designed by XMOS. It is a 32-bit quad-core processor, where each core runs up to 8 concurrent threads. It was available as of Autumn 2008 running at 400 MHz. Each thread can run at up to 100 MHz; four threads follow each other through the pipeline, resulting in a top speed of 1.6 GIPS for four cores if 16 threads are running. The XS1-G4 is a distributed memory multi core processor, requiring the end user and compiler to deal with data distribution. When more than 4 threads execute, the 400 MIPS of each core is equally distributed over all active threads. This allows the use of extra threads in order to hide latency. The XS1-G4 comprises four cores and a switch. Each core has a data path, a memory, and register banks for eight threads. Threads running on different cores can communicate with each other by exchanging messages through the switches.