The PDT-11 series existed in three different models, PDT-11/110, PDT-11/130, and the one described here, PDT-11/150.
The PDT-11/110 is like the VT100 terminal and has no disk or tape drives in its housing. You need some sort of connection to a network to download a boot image to start the machine. The PDT-11/130 is also like the VT100 terminal, but includes a TU58 cartridge tape drive from which the machine can boot (slowly). The PDT-11/150 is the biggest machine in this series, and is housed in a box, not a VT100 (although you can connect a VT100 to it), with two 8-inch floppy disk drives stacked above each other.
The floppy drives have a red stripe on the handle, because they are a little different compared to the regular RX01 disk drives. The floppy drives are single-sided single-density 8" drives (not based on the RX01 or RX02 floppy drive), but they are compatible with RX01 format and have an interface that is sort-of RX11-like. Alas, the interface is not compatible with the RX11.
I have read that there seemed to exist a single-drive variant of the PDT-11/150 (cheaper unit), but I never saw it.

The PDT-11 runs a stripped down version of RT11. The PDT-11/130 and PDT-11/150 use the same PD.SYS driver in RT-11, with help from standardized ROM which handles the hardware-specific stuff (either a not-quite-RXV11 at CSR address 177170 or, even weirder, a not-quite-DLV11, also at CSR address 177170)   info: John Wilson.
The PDT-11/150 cannot boot from a regular RT11 floppy. The RXT11 controller is not quite compatible with the RXV11, even though it is generally similar. The PDT-11 boot disk needs   COPY/BOOT:PD RT11FB.SYS DX0:   since the DX: bootstrap and driver will not work. The SJ or FB monitor *is* vanilla though.

There is a way to make a PDT-11/150 boot disk using a normal RT11 distribution kit. One of the floppies in the RX01 distribution kit is bootable on the PDT-11 (that is not the main boot floppy, which is for an RX11 or RXV11). There are special drivers for the floppies and a special boot block.   COPY/BOOT:PD RT11SJ.SYS PD0:   (or RT11FB.SYS).

The I/O page of the PDT-11 is emulated by the 8085A processor (this is why I/O page references are crazy expensive on a PDT-11, they take dozens of usec) so the peripherals are all faked in firmware and it might as well have been a totally vanilla RXV11.