I hope Warren's emailer lets this pass through.  

Here is a picture of the original root 'ROM' for the PDP-11 M792-xx board, which gives you 32 words (64 bytes) of memory.  It used individual diodes in or out arranged an array to represent individual bits with a diode present being a '1' and '0' if missing.  As the Gunkies web page suggests, the board came in two versions - customer programmable which was fully populated with diodes, and the user removed unneeded diodes to program it.  The other variants were programmed with the designed boot functions - designated M792-Yx (where 'x' is a capital letter, starting with 'A') 

Also,  remember that a $3-5k/drive RK05 is only 2.5Mbytes [4872 512 byte 'sectors' a.k.a. disk blocks -- 2 hd/disk * 15 sec/cyl * 203 cyl/disk], which is why we had separated /bin and /usr/bin and /lib and /usr/lib.  Plus, as Norman points our dynamic linking only comes later, so all of these are static bound programs (i.e., Sun create /bin and /sbin to separate those programs).  The whole idea was what was in root was enough to get the system running in /bin, /lib and /etc and everything else was one the mounted file system, which often was another RK05.   Many of our V6 and V7 systems ran with 3 RK05 /, /usr /home, and we might have an extra RK05 for /mnt.  Tape was the standard thing.   DEC tape was cheaper than 9-track, although in my history, we all went for 9-track because it was more portable to other systems, but often used after-market 9-track transports that emulated the DEC ones.

Even with the VAX, the front-end runs on an LSI-11 with floppies, so things like microcode were loaded into the VAX and stored in ROM.   By then, the RP and RM series had become more normal, and eventually, the RK07 and RL02 replaced the RK05.   But we are not talking about substantial capacity in the storage systems.   Only ten years later, in the early 1980s, a Fujisu 'Eagle' is just 470Mbytes and costs 12-15K per drive, plus another $6-8K for the controller for your Vax [also often after-market from SI or Emulex].

Sun and Apollo build 'diskless' systems because a 100MB ST-506 style disk was considered too expensive, and was worried about the entry-level price of their systems (I famously made a typo describing how those systems performed BTW with a dyslexic change of the s to c on a whole company email at Masscomp in the mid-1980s - to Sun's credit, it was the best marketing ploy ever - people bought diskless and discovered they sucked and then all added a disk - which cost more $s than the original Masscomp system which was had one built-in).  But I digress...

Those new workstations did have real ROM chips, unlike the original PDP-11s, but they were small, maybe 8Kbytes of NS2764, so the ROMs were tight and only had enough in them to recognize a couple of peripherals.

So to answer more of your question, you build the tools you need that make sense at the time.   /stand was a simple solution and was small.   For V7 and the original BSD 3 and 4 released, the user needed to read a distribution media, traditionally a 9-track tape, and set up a local disk.  The number of peripherals was small. 

One other thought ... in the case of the PDP-11 and Vaxen, the disks were often dismountable, like the different RK, RL, RP, and RM series drives.   We often had more than one system.  So once the system was up and running, it was not usual to use a different system with better tools to help repair things if bad stuff occurred.  That is also why we often used 9-track tape, just because that was even easier to move back and forth.  With the Wokstrations, the disks were generally sealed. 

Clem

A  small PS on another note -- I have memories of taking an ST-506 disk with me to France to work with some engineers in Grenoble and explaining to the French authorities that they could not open it up to look inside.     BTW: this pre-internet - imagine what we had to do if we flew to Canada, which was taxing SW.   Even bringing tapes in and out of Toronto airport could be treacherous.