HP-41 MCode Question

[hth]

I have a far fetched theory. HP saved some transistors in their RAM chips and as this it the T register, it written to more often than it is read. Reading is done when dropping and rotating the stack. The cost in ROM for this is max 4 instructions.

ENTER or numeric input lifts the stack, which means it writes a lot more to T more than it is read, so the being able to write to it is more important than reading it. The C=0, RAMSLCT (DADD=C) selects T and chip 0, so it may also become selected for free, which may be taken advantage of, depending on the firmware.

Anyone who spots old HP engineers at the conferences can try to ask if anyone knows the real answer.