A motherboard has four DIMM slots; three slots are gray and the fourth is black. What type of memory is this board designed to use?

A motherboard will require DDR3 type of memory.

Explanation:

In the motherboard, we use DDR3 RAM. It stands for "Double Data Rate 3" full name of this ram is DDR3 SDRAM where SDRAM stands for "Synchronous Dynamic Random-Access Memory". It was firstly implemented in the 1970s.

DRAM is not clock-controlled. The DRAM is asynchronous RAM i. e. with no Synchronous replication of external stimulus.