I am doing research to build a gaming pc next year and have a question that I would like to ask. I plan to have an SSD and 2 HDDs installed. The book that I read about building PCs says that I should look for an SSD and HDD with similar or identical bandwidths. Could someone please tell me what they mean by similar or identical bandwidths? Thanks.
You will not find any HDD that has the bandwidth of a modern SSD. SSDs (even old models) can transfer data far faster than HDDs.
What you really should look for is a good SSD (opinions vary, but I like Samsung, Crucial and Intel) and a couple (do you really need 2 or will one 3Tb work?) HDDs of good quality, which is pretty much any of them today.
The SSD will be fast enough to make use of SATA III (6Gbps), but no HDD can even saturate a SATA II (3Gbps) connection so it doesn't matter which SATA ports they are on.