using new technology on old machines. Was: PDP-12 Restoration at the RICM

[tony duell]

> >
> > I am of course counting all the transistors inside that chip.
> 
> Well, that was obvious. But it raises an interesting point, today you
> can cram a whole computer in the footprint of the simplest DIP carrier.
> For the same price point and same reliablity. Is it then overkill if you
> choose to use thousands of those transistor over using just 10 ?

Is it as reliable, though? You will get no argument from me that the _same design_
is more reliable the more 'LSI' it is -- that is a processor as a single chip is more
reliable than the same design in TTL which in turn is more reliable than the same design
in discrete transistors. But when you compare different designs, I am not conviced. My 
experience is that I have had to replace many more LSI ICs than TTL and many more TTL chips
than transistors (power transistors, choppers, line output transistors excpeted!). I am not at all 
convinced that a microcontroller is as reliable as a 555 timer. After all, microcontrollers presumably
store their firmware in some kind of flash memory which is going to suffer from bit-rot. A 555
doesn't.

> Similar to Mark's example of using just the first bytes of an SD card
> with gigabytes of storage.

Again, I wonder if the data retention time decreases as the number of bits
per device increases. Intuitively it should. Mind you, any SD card is probably
going to be more reliable than a real TU58 tape now :-)

-tony