On Tue, 28 Nov 2017, Clem Cole wrote:

> ​Hmm, so was dot, which is what TSS and MTS used.​  DEC was using it as 
> the <base>.<ext> separator, but I think Ken could have used it as easily 
> at the time since the idea of <ext> and exposing semantics of what the 
> file was in the name was foreign to UNIX (although was used in other 
> systems as we know).

OS/360's JCL used "." (partitioned datasets?) such as SYS1.WATFIV.blah and 
so on.

-- 
Dave Horsfall DTM (VK2KFU)  "Those who don't understand security will suffer."