The Dell Poweredge T420 Server has a few different hard drive backplane options. The options are 4x 3.5, 8x 3.5, 16x 2.5. The backplanes can use a variety of drives. SAS, SATA, NL SAS, and SSD Drives. The replacement backplane needs to be the same as the one currently installed as the chassis dictates which one will physically fit. Always replace with a genuine Dell backplane which all the backplanes listed here are all Dell original parts. If you have any questions on Dell replacement parts call us at 952-831-1032. Phones are answered Monday-Friday 8AM-5:30PM.