I programmed a complete Property-Tax accounting system on one of these IBM 5120 computers, back in 1982... for City Hall in the town where I was living. The 5120 had 32K, no hard drive, just two 8-inch floppy disks, for programs and data. So: no real operating system either. It booted from ROM, and gave you a prompt in APL or BASIC.
As I recall, the style of BASIC was very limited/simplistic. For instance: no "FOR" looping, just use conditional branching. The "IF" statement only had syntax: "IF ABC $ X THEN 2500" where 2500 was a line number to GOTO when the IF-conditional was true. Even the 5120 Disk access was crude. IBM re-used old tape drivers, so the floppy disks would only understand FIXED length FILES, pre-allocated when created... so you needed to plan the Max size for a file in advance, and if that filled up, "too bad" you can''t extend file length... gotta re-build allocations, and copy to another 8" floppy.
However, despite computer''s limitations, I designed and coded a solid Tax accounting system that tracked property owner/address/value/zone for the whole town, calculated taxes, printed mailer statements, collected taxes, logged fees/fines, and allocated funds to appropriate city funds $ levees... which was running for as long as they kept the computer.
The IBM PC was brand new at the time, with more memory and a hard drive, and would have been a better choice$ but managers had already purchased the 5120, and stuck with it.
I guess one of the things I learned from that project is that the right skill for coding/design/efficiency/usability can make more difference than the computer it''s running on... and THAT remains true for system many years later.