I also deliberately left out the phase change that was caused by IBM including 1401 Emulation in System 360. Before that, everyone rewrote their programs every

I also deliberately left out the phase change that was caused by IBM including 1401 Emulation in System 360. Before that, everyone rewrote their programs every time a new machine came out, because it was expected it would be incompatible with the old one, so we have a ton of code still running that wasn't expected to last more than 10 years when it was written, in the late 1950s, early 1960s.