Appendix D
Program Memory Storage Requirements
and LAST X Operations
Program memory in the HP-41C is structured in registers. Each register can hold up to seven lines of program instructions. In other words, each register in program memory is divided into seven parts. One of these parts is called a byte of program memory.
Program Memory
contains 7
 byte 1
 byte 2
 byte 3
 byte 4
 byte 5
 byte 6
 byte 7
Most operations on the HP-41C require only one byte or program memory for storage as a line in a program, but some require two or even more bytes. For your reference, the number of bytes required for storing each programmable HP-41C function is listed in the table beginning below. The operations are listed in alphabetical order of their name.
Note that ALPHA characters require one byte each plus an additional byte for string when stored in program memory. So the string CIRCLE would require seven bytes of program memory. Each digit in a number requires one byte when stored in program memory. The decimal point in a numbers also requires one byte. The number 28.741 would require six bytes of program memory.
Also indicated for each operation is whether the contents of the X-register are copied into the LAST X register before the operations is performed.
      Requirement   Saves x  
  Function   (Bytes)   in LAST X  
  ABS    1   Yes  
  Σ–    1   Yes  
  Σ+    1   Yes  
   +     1   Yes  
  ADV    1   No