the article here ends around 1971 --- the mainframe would later save IBM again, twice, once when they replaced aluminum with copper in interconnects, and then when some crazy IBM Fellow had a team port Linux to s390. Which marked the birth of "enterprise Linux", i.e. Linux running the data centre, for real.
Did it though? Or was it the gradual phasing out of mainframe-class hardware in favour of PC-compatible servers and the death of commercial Unices?
Proprietary Unix is still around. Solaris, HP-UX and AIX still make money for their owners and there are lots of places running those on brand-new metal. You are right, however, that Linux displaced most of the proprietary Unixes, as well as Windows and whatever was left of the minicomputer business that wasn't first killed by the unixes. I'm not sure when exactly people started talking about "Enterprise Linux".
Oracle's big reason for doing so was because they could charge more for Oracle on Linux, and still get to a lower total cost of ownership than Oracle on Solaris.
Oracle began this in 1998. By 2006 they had their own Oracle Enterprise Linux distribution.
and that pulled all other vendors along, HP, Dell, Fujitsu, likewise for software...
and it all started with IBM officially supporting and pushing the hobbyist student project Linux on the holy Grail of enterprise compute, (of 1999/2000): s390
4.3BSD was basically designed without any bespoke hardware platform of its own. They commandeered DEC’s big iron, for the most part, to “dual boot” before dual-booting was cool. 386BSD began to enable PC-compatible hardware and really cost-effective “server farms” even before Linus was a twinkle in Finland’s eye.
Moreover, various BSD flavors were empowering admins to breathe new life into legacy hardware, sidestepping and bypassing the proprietary software channels. Linux, on the gripping hand, remained x86-unportable for awhile after BSD (and Xfree86) was running everywhere.
Personally I ran Minix-286 at home; at university we enjoyed a “recreational” VAX11 running not VMS but 4.3BSD.
Flash forward to 1998: from the arid but air-conditioned Sonoran Desert I received gently-loved twinned Apollo 425t systems with memory upgrades; I installed OpenBSD on both, as well as my 486DX100! It was a homogeneous OS environment with heterogenous hardware... and the 486, with Adaptec SCSI & a VLB #9GXE64 Pro, could boot into Windows 98 and run the Cygwin X server, or DOOM or Quake.
There was a golden age when a dude could walk into any surplus yard, grab Big Iron Unix Boxes, take them home and bootstrap NetBSD. On anything. Bonus: BSD originated in USA/Canada, for a trustworthy chain of trust. (Oh Lord, the encryption export technicalities...)
Linus played follow-the-leader for years.
-- https://en.wikipedia.org/wiki/History_of_Linux
It was all about Solaris, AIX and HP-UX for .com businesses.
I was there, our Linux deployements were only used internally, we never sold those workloads as UNIX targets on our product.