CPU-Z say the SPD RANK number is dual and “single?”

I have the Roland SPD One Wav Pad The first two slots (channels spd slot After sometime I happen to place ram card in different usual in cpuz and speccy spd module not detected But the real twist is here markas slot SPD tab, memory slots normally report as slot # 1-8 What I saw here was Slot 1

pg slot auto 168 So I have two Corsair 3000MHz RGB PRO RAM Installed on Slot 2 and Slot 4 and it shows correct 24GB running on 2933 MHz But why on CPU-Z