A Brief bit about System on a Chip(SoC)
System on a chip is the trend we are going towards and here is it explained. Also I highly recommend you check out Intel's paper on the platform controller hub; https://www.intel.com/content/dam/www...
There is also AMDs paper on HyperTransport Bus that applies to this; https://www.all-electronics.de/wp-con...
Also do a image search between an old IBM and a mini itx board, you'll be amazed.