Registers that contained intermediate results or other codes related to pending operations were accessible in several Texas Instruments calculators. On the SR-52, these registers were explicitly numbered and could be accessed through the STO and RCL keys. On the TI-58/59, they were more hidden; access was possible through the undocumented HIR instruction, which had to be "synthesized" in program memory. On the TI-88, these registers were well documented, and accessing them was possible under program control through synthesized instructions described in the manual. Sadly, on later models such as the TI-66, access to these registers was explicitly disabled, along with the ability to synthesize undocumented instruction codes in program memory.

The following is a list of the TI-88 hierarchy registers:

00-07   AOS stack entries
08-14   Statistical registers
15-25   Reserved for system operations
26   Digit position 7 is the language code; position 8 is the subroutine pointer; rest is reserved for system operations
27   Reserved for system operations
28-32   Subroutine stack
33-43   Reserved for system operations
44   Digit position 5 is the cursor location; rest is reserved for system operations
45-46   Display registers
47-48   Reserved for system operations
49   Utility register
50   Auxiliary operator stack
51-52   Reserved for system operations
53   Numeric display register
54-55   Reserved for system operations
56   Operator stack
57-62   Reserved for system operations