Don't know the PDP-10?  Here's a very short overview ... since you know how to g**gle, I just foward a short presentation of stolen pictures:

 

The PDP-10 was a very influential mainframe of DEC in the 1970's. It began all with the PDP-6 in 1964 (not pictured here). Very few machines were build.

 

pdp10 ka10 full

There were basically four different models. They are most easy to distinguish by their front panels:

"KA10", introduced in 1967:

pdp10 ka10 console

 

"KI10", 1971:

pdp10 ki10 full

 

"KL10", 1974 (no panel anymore, but a repainted PDP-11/40 as console processor instead):

pdp10 kl10 console

And finally "KS10",  1979. (Sold as DECsystem-20, hence an orange case. No controls, processor and memory fits in one rack.)

pdp10 ks10

 

There were also several clones (Foonly, Xerox PARC's MAXC) running TENEX (the BBN operating system), as well as clones running DEC's operating systems
(System Concepts, XKL) Tops-10 and TOPS-20.  XKL eventually came to own the IP, and still uses the PDP-10 architecture and TOPS-20 in part of their high-end
router products.