Some random thoughts, and items of historical interest.
I was showing this to my son last night. He is a professional programmer with focus on UI, and was 3 when I bought the TEF10. Watching this work in a 64KB memory space elicited blank stares; "I don’t know of a single device I own that could run on even 100 times that much memory."
It's amazing what can be done in a 64k memory space if you set your mind(s) to it.
In use, there is a lot of disk activity, swapping program modules in and out. Really slows things down. This thing would benefit hugely from an SSD.
Some historical context: When the TEF10 was released, the IBM PC was already out and taking the world by storm. As you can imagine, Tecron took a lot of flack for coming out with a Z80 CP/M-based system, especially considering the price point. So why did they?
: You can't keep, or control, time accurately with an 8086/8088, because of the prefetch buffer (called pipelining back then); instructions don't always execute in exactly the same number of clock cycles. But you can with the Z80.
: Also, as I understand it, development of the system started in 1979, well before the PC was a "thing".
Not many TEF-10's still exist, because Tecron made a concerted effort to remove them from the market. They didn't want to (or couldn't guarantee being able to) service them. They did this by offering a generous tradein allowance to owners to upgrade to a TEF12, and later, TEF20. (I believe availability of the 720k floppy drives played a major part in this; they switched to the 1.2MB drives in the TEF12).
A note on serial numbers. The serial number on the back of the unit (22288) is not exclusive to this product. The only estimate I've heard is, they made around 175 TEF-10's. That number seems low to me. The only way to know, and to know where a particular unit falls in the sequence of release, is to look at the last digits of the CP/M license number, which were issued in order and written on the software distribution disks that came with the unit. This unit is #00007, one of the "pre-production" units offered.