I think of it more as a continuum. At MIT under Jack Dennis, a pdp-1 was converted to timesharing. https://www.computerhistory.org/pdp-1/timesharing/ https://

I think of it more as a continuum. At MIT under Jack Dennis, a pdp-1 was converted to timesharing. https://www.computerhistory.org/pdp-1/timesharing/ https://www.computerhistory.org/pdp-1/timesharing/ John McCarthy discusses his memories of early timesharing systems, mentioning the pdp-1 https://www-formal.stanford.edu/jmc/history/timesharing/timesharing.html https://www-formal.stanford.edu/jmc/history/timesharing/time... https://web.mit.edu/Saltzer/www/publications/protection/State.html https://web.mit.edu/Saltzer/www/publications/protection/Stat... discusses protection hardware -- and how the 360 actually mostly used it on main memory, not on IO channels (even though there was protection available to IO channels). I'm mainly saying that there were many 'experiments' tried in the olden days, and those plus "the market" give us what we have today. Recall, in the days of the IBM 1401 and DEC pdp-1, the notion of 'byte' as an 8-bit quantity did not exist. ASCII did not exist. The IBM 1401 was a Decimal / Character machine, and could add/sub/mul/div numbers of arbitrary length, in hardware (!). The pdp-1 used one's complement arithmetic. On and On...