This is the info I got from Calum by email when I contacted him awhile back.
The Basic ROM board is a daughterboard based on two ROM chips. To
reprogram this board you need to physically remove the chips and use a
ROM burner. This is really an option for people that want to run an
off-the-shelf program without changing it, and who might only
occasionally want to change their setup.
The Realtime daughterboard is totally different. There are no ROM chips
and no burning with this board, much more advanced. This is aimed at
people who want to spend time on a dyno really getting the most out of
their tune.
The Realtime ECU uses a single USB connection (it has a permanently
attached 6ft USB cable) that adds two new virtual com ports to your
laptop when you connect. One is a standard consult connection (works
with all existing consult software), and the other is the for the
eumlation stuff. There are no ROM chips on the board, and you don't ever
open the ECU lid. The emulation side supports a subset of the Romulator
protocol, and EmUtility and TunerProRT both work great with it. The
emulator protocol is also open if you want to write your own custom
software (the command set is pretty straightforward). I use TunerProRT
for realtime tuning, Nissan DataScan for map tracing and general consult
functions, and good old CalumSult for datalogging.
All changes can be done 'realtime', while the engine is running. Makes
tuning k-values and such pretty quick. You can also upload your bin to
the ecu without the ecu being installed in the car, it will power off
the USB port.
The consult circuit is also 'smart': when not connected to a laptop it
automatically shuts down, so you can use an external consult device
(techtom, n-probe, real CONSULT unit, etc).
And thats all it does. No extra features, no bells and whistles, no
firmware updates, just pure tuning.