You clearly missed out on the PDP-11 era, and you have my condolences. The PDP-11 was IMO the finest of the mini-computers, and I was sad when memory got so cheap that the PDP-11's 16-bit addressing range (w/o segmentation) made it obsolete. PDP-11 was an elegant, very regular architecture that was so simple that PDP-11 ASM programming was often easier than with the high-level languages of the time (this was before Pascal and C). The machine language had such a simple octal coding that many ASM programmers could instantly decode instructions from an octal dump.
And I/O! PDP-11 had very simple memory-mapped I/O. How simple? If you have an extra 10 minutes, go to the IT library, take out the "PDP-11 Peripherals Handbook" and read the chapter called "Programming". It will show you how to do both busy-wait and interrupt-driven programming, in JUST 8 PAGES. Compare that to what it takes to write a device driver for your favorite OS.
Looking at PDP-11 books reminds people like me of the wonderful time between the aloofness of mainframes locked away in glass rooms and the insane overcomplexity of modern desktop computers. The PDP-11 was simple enough that an individual could quickly master it without being bogged down in arbitrary complexity. It was a great time of freedom -- a machine you could fully control before being handcuffed by DRMs and software patents.
You can still get a PDP-11 style joy of simplicity with bare-metal programming on some embedded processors.
The Digital Equipment Corporation , the well known name in computers for decades is history now. So much so that today's generation will hardly have heard this name.
But my IT department's library has a complete rack assigned for the books , manuals of DEC PDP 11 series computer and the associated RSX-11 operating system. It competes for space among the latest additions on HTML, XNL, JAVA and such new additions.
The veterans in our department refuse to dump those obsolete manuals !
I've always loved this desk plaque that was originally my father-in-laws, who started out in engineering in the 1950s. It is a treasured item that will be passed down through generations of "pack rats" in the family!