A chiplet is a sub processing unit, usually controlled by a I/O controller chip on the same package. Chiplet design is a modular approach to building processors. Both AMD and Intel, current major CPU manufacturers, are adopting chiplet designs for their current product line ups. Chiplets help increase production by way of better silicon yields. Higher yields and modular building mean a producing high core count parts mean less waste.
Chiplets allow manufacturers to increase yields of chips over monolithic CPU designs where all pieces of a processing unit are built into a single piece of silicon. The increase in yields is because a single monolithic chip with a defect on a core will either have to be sold as a lower model with fewer cores or thrown out entirely. With the chiplet approach, a single defective chiplet is discarded and CPU can be sold as the desired model by adding more cores.
Chiplet designs also stand to optimize production by way of using different photolithographic processes for different the I/O and chiplets. A chiplet may be one of a number of similar units on separate pieces of silicon to which threads are offloaded for processing. These high power consumption devices benefit most from newer processes where they may be able to operate with higher frequencies, with lower power consumption or with some balance between the two. The I/O die has connectivity to the memory through the memory controller and peripheral connectivity through the systems bus, such as AMD’s Infinity Fabric. Both memory controllers and Infinity Fabric are difficult to scale below 14nm and see less benefit from this transition. Intel is also taking a modular approach to processors with 3D stacking, allowing chiplets to be manufactured in vertical stacks as well.