Apple Mac-based servers... Kind of a rare beast, not many of 'em were made I don't think. I think they were an early 2000s thing, if I'm not mistaken. Not very successful, probably due to the unhappy combination of Apple's staunchly closed-box approach to computing hardware, lack of demand and support and the HUGE pre-existing base of x86, POWER and Sparc machines, most notably those from IBM, Dell, HP, Sun, DEC and Compaq (the last two were still separate independent companies at that time). Price was likely to have been a contributing factor as well. Very neat photo.
These serves were beasts. I ran services on them for years and I still have some running as task servers in my lab at the office. Redundant parts, fast-swap capabilities, fault tolerance, built in hardware RAID, LOM, remote setup; one even survived a "hot RAM swap" done by a clueless tech. They were on-par with many of the PC 1U servers in the early 2000s. If you needed Mac OS in the datacenter, Xserve was fantastic! The alternative was to burn a 5U shelf for a G5 tower or go with a underpowered MacMini, or Kevin forbid, rack an iMac or PowerBook.... The Xserve died because Apple internally lost interest and reprioritized to consumer products. The server team was cut way back and the whole concept of the RackMac died. At least till Apple released the current MacPro... which is powerful... but not a datacenter class device at all.
Yeah, I don't think a MacPro (or anything Mac-like, to be honest) these days can be sensibly classed as "data center-grade" really. Not to mention the obvious fact that back when Apple was developing the XServe, it was still kind of possible to repair Mac computers. Nowadays, that's almost impossible, no thanks at all to Apple swearing by the planned obsolescence model to the point of actively denying third-party techs access to basic needs like the schematic diagrams and "board views" (the actual plan and layout photos or drawings of the boards showing the actual physical placement of the various chips and other components on them), re-programming software and tools and the actual chips required to get Mac boards working again. I don't think that thinking would be looked on with adoration among today's enterprise IT people given that they can't deal with "just buy another server" whenever some chip or add-on card goes bad. If you think being forced into buying a whole new laptop or desktop for some $1,000 to $2,000 any time the mainboard dies after a year or less of service, imagine how well that would go over for an IT guy (or gal) servicing a server or mainframe costing $150,000 and up. Yeah, not very well. Not that the other companies are very much better, but Apple is one of the ones who started that and the whole industry is "monkey see, monkey do" - whatever one does, they all inevitably end up doing. Anyway, didn't intend to go off on a rant like that. Glad that you have preserved your Apple XServe boxes and may they continue to Live Long and Prosper, in your caring hands of course.
Since you mentioned MacMinis, I'd like to note that people today do still use them and some actually use them as nodes in data centers. Very strange. But then again, you might also find Raspberry Pi boxes and boards in DCs as well. I guess computing technology has advanced enough to the point where a Raspberry Pi can theoretically be used as a server of a sort, albeit an EXTREMELY limited-capability one.
I distinctly remember an 8-Bit Guy episode on YouTube where he essentially described smartphones as being pocket-sized supercomputers, with as much power as or more than a classic Cray machine. Of course the same advances that gave us smartphones with near-laptop level performance and capability have also resulted in the million-plus core monsters that now classify as supercomputers.
My MSI Bravo 17 laptop with its 8-core/16-thread CPU is EASILY more powerful than even the best 1990s era supercomputer. I know that's nothing in the face of all the 128-plus core servers, but to me that's pretty huge all the same, especially given that my previous two laptops had only two cores in their processors. The fact that my own personal machine is powerful enough to run 64-bit VMs without any issues is mind-blowing on its own.
Yep, I'm one of them who hosts MacMinis in DCs! Some software services like Apple Caching services or Xcode server require macOS to run. At least currently, it's against Apple's ToS to virtualize macOS on non-Apple hardware. Otherwise I'd just use a normal hypervisor cluster...
Between miniaturization and optimizations like SSD/DDR4, it's crazy the computational power in modern smartphones compared to older supercomputers.