Usually the story is they're running something like CNC control which originally ran on baremetal, then got virtualized onto VMware when the hardware died (possibly using VDI to make it appear on a terminal close to the machien), and it's still doing the same thing effectively today.

In some cases you can do zero copy conversions, so downtime can be done in a few minutes, but it relies on the customer have very particular storage configurations (NetApp basically). In other cases there can be significant downtime that needs to be scheduled. I worked one case where the customer shut down several production lines over a number of weekends so we could convert the workloads. (Everything was meticulously planned, along with fallbacks that thankfully we did not need to use.)

Some things you don't convert at all. Databases generally get replicated at DB level to new hardware. Single-purpose appliances need to be reprovisioned by going back to the vendor and asking for a KVM equivalent.

Then there's all kinds of craziness, like we had customers who rolled their own backup solutions where we had to add special cases to the software to detect and ignore the backup partitions. Or people running Windows 95 or RHEL 3 (for real!) where there are no virtio drivers and we don't certify the hypervisor so it requires support exceptions. At this point people have been using VMware for nearly 30 years, there's all kinds of crazy legacy.

It's all based around open source projects virt-v2v and Migration Toolkit for Virt, and the typical target is OpenShift Virtualization.

There are various zero-copy options if you're using specific storage. In the best case the downtime for each guest can be as little as a few minutes. If the storage stars don't align then it can take a few hours per VM (but conversions happen in parallel, dozens or hundreds at a time).

[I don't have any specific knowledge about where this Tesco account is going. We have plenty of competitors. Everyone is dining at the Broadcom trough right now. Broadcom's "strategy" is absolutely baffling to me.]

Edit: Almost forgot that I gave a 5 minute lightning talk about it: https://pretalx.com/devconf-cz-2024/talk/SN93LG/

And in case you're thinking this all sounds very inefficient, the same company still exists today.

What are the chances of that happening today for anyone not in the C-suite?

I never had a private office until I started working from home. My pension comes out of my salary and all the risk of markets falling etc falls on my shoulders.

Even to their home country.