[TUHS] Abstractions

[Dave Horsfall]

On Sat, 20 Feb 2021, M Douglas McIlroy wrote:

>>  - separation of code and data using read-only and read/write file
>>  systems
>
> I'll bite. How do you install code in a read-only file system? And where 
> does a.out go?

I once worked for a place who reckoned that /bin and /lib etc ought to be 
in an EEPROM; I reckon that he was right (Penguin/OS dumps everything 
under /usr/bin, for example).

> My guess is that /bin is in a file system of its own. Executables from 
> /letc and /lib are probably there too. On the other hand, I guess users' 
> personal code is still read/write.

That's how we ran our RK-05 11/40s since Ed 5...  Good fun writing a DJ-11 
driver from the DH-11 source; even more fun when I wrote a UT-200 driver 
from the manual alone (I'm sure that "ei.c" is Out There Somewhere), 
junking IanJ's driver.

The war stories that I could tell...

> I agree that such an arrangement is prudent. I don't see a way, though, 
> to update bin without disrupting most running programs.

Change is inevitable; the trick is to minimise the disruption.

-- Dave, who carried RK-05s all over the UNSW campus