There were three generations of main memory systems for the PDP-10; the first two with the so-called external memory bus, in 18- and 22-bit address forms (for the KA10. and KI10 and early KL10, respectively - there were minor differences between the two, requiring a KI10-M Memory Bus Adapter if the two are mixed), and the internal 'S-bus' (for the later KL10). (Memory for the KS10, which was sui generis, is not covered here.)
The first two groups are all multi-port memory (generally 4 ports per memory system); the CPU uses one port, the others are used by channels for mass storage such as disks. All except the MF20 and MG20 were core memory, and almost all supported parity, and some level of interleaving.