They sold very expensive devices that were actually an off-the-shelf 1U PC with custom software (which provided the real value). The problem — and this dates it — was that the PCs had a game port¹, which gave away that this custom hardware was really just a regular consumer PC. So they had some fancy plastic panels made to clip on the front and hide the game port.
(With Unisys specifically, at one point they still made physical CPUs for high end models, but low end models were software emulation on x86; I’m not sure what they are doing right now.)
It was my first exposure to this sort of thing, and I was taken aback by the costs of this stuff, which made the Sun gear I worked with look extremely cheap :)
Given the shrinking market share of mainframes, the only way for vendors to continue to make money is to increase prices on those customers who remain – which, of course, gives them greater encouragement to migrate away, but for some customers the migration costs are going to be so high that it is still cheaper to pay megabucks to the mainframe vendor than do that migration. With emulated systems like the ones you saw, the high costs are not really for the hardware, they are for the mainframe emulation software, mainframe operating system, etc, but it is all sold together as a package.
At least IBM mainframes have a big enough history of popularity, that there are a lot of tools out there (and entire consulting businesses) to assist with porting IBM mainframe applications to more mainstream platforms. For the remaining non-IBM mainframe platforms (Unisys, Bull, Fujitsu, etc), a lot less tools and skilled warm bodies are available, which I imagine could make these platforms more expensive to migrate away from than IBM's.
I made the terrible mistake of jumping too far between versions and the update broke iDrac and thus the server. There was no warning on Dell's website nor any when I applied the update. I only found out what happened after some googling where I found the upgrade path I should have taken.
This is just terrible quality control and software engineering.
Since they just wanted to add some new features on top and present a better rack-based interface to the user, they decided to build a bigger box, put one of the old devices inside the box, then put a modern PC in there, and just link the two devices together with ethernet through an internal hub also connected to the backpanel port and call it a day.
The problem is, if you do an update, you need both the "front end" and the "back end" to coordinate their reboot. The vendor decided to fix this by adding a simple URL to the "backend" named: /backdoor/<product>Reboot?UUID=<fixed uuid>
Their sales team was not happy when I showed them an automated tool in a few lines of ruby that scans the network for backend devices and then just constantly reboots them.
They still sell this product today. We did not buy one.