GS wrote:

Such things as cash registers and the like (POS devices) usually have
their own proprietary software pre-installed which is typically not
Windows (or even Linux). I have written POS apps that run under
Windows on PCs, some tied to accounting software either 3rd party or
included in my app. Any Excel-based versions are also available as
stand-alone EXEs for users that don't use MS Office.

I've seen cash registers and POS terminals getting booted and saw
Windows coming up. However, this is not the full end-user version but
stripped to basic functionality aka Windows Embedded [Standard].

An OS is needed to run the POS. I've not seen commercial POSes that
provided their own boot manager, dispatcher, and all other features of
an OS. They don't want to also dev an OS to sell their POS. They don't
even tell their customers what OS is used because the customers never
supposed to be working at that level. Even enterprise-grade comm
controllers that I've worked on had their own proprietary software but
ran on some variant of UNIX or Linux, and required some special method
to get at the OS level (although that was still controlled by an
interface that restricted what could be done).

I don't know what minimal Windows functionality is needed for Excel.
Maybe Windows Embedded [Standard, Pro, Enterprise] is needed. Windows
Embedded Compact aka Windows CE (for consumer electronics, gaming
consoles, digital receivers, set-top boxes) and Windows Embedded
Automotive (variant of Compact for embedded systems in cars), and
Windows Embedded Handheld (portable devices, like used by delivery
companies where you sign a pad) don't seem like they'd be appropriate to
run Excel. Of course, the full edition of Windows could be installed
(but often stripped of all superfluous software for a POS, like
Calculator, Paint, Notepad, and other non-OS fluff).