HP vs TI Indirect Addressing.

[Dave Britten]

I agree that it's probably because of the fixed instruction sizes on the 65 (6 bits), 67/97 (1 byte), 11C (1 byte), 29C/19C (1 byte?), etc. (Interestingly, the 15C does have some two-byte instructions, but it still has a dedicated indirect address register.)

If I'm remembering correctly, the TI-59 could take this to ridiculous extremes with INV DSZ IND XX IND YY, which would be "decrement the indirect register specified in register XX, and branch indirectly to the step specified in register YY on zero". A whopping SIX bytes/steps for one program instruction! So TI might have been wasteful with memory having so many unmerged instructions, but it did offer some interesting flexibility such as this.