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I have an HP41CV with a card reader but this is becoming less reliable with age and I would like to increase the memory to store programmes which I use frequently. I understand that I need to fit an Extended Function/Memory module (82180A) first before adding Expanded memory modules (82181A). Is this correct ? Is there any apparent difference to the user when accessing data stored in this memory ? Thanks

The extended memory is not access in the same manner as the main memory in the 41CV. Special commands swap memory between main and extended. Programs, etc. can only be run from within main, standard memory. The extended memory is for temporary archiving. Be aware the extended memory space can be lost and you should have backups... Your card reader probably needs a roller replacement (repair).

Charles, here is a little bit more info. You are correct about the modules. The 82180A (Extended Function/Memory module) adds the functions to access the extended memory, some other nice functions that make programming easier, as well as 124 usable registers of extended memory. Two HP82181A (Extended Memory) modules may be installed once you have the 82180A installed, and each of these modules adds 238 usable registers to extended memory, for a total of 600 usable registers extended memory. The memory essentially operates like offline disk, or card reader memory. When you want to run a program, it has to be recalled into main memory, using functions in the 82180A. However, there are sythetic methods of executing programs from extended memory, but there may be a limitation of only being able to use the first 124 registers in this manner. BTW, I don't have any 82180A's, but I do have an extra 82181A that I would consider selling. An alternative would be to burn your programs into a 16K EPROM. In this manner they are non-volatile, use no user memory whatsoever, and 16K (the equivalent of over 2000 memory registers) is available for program storage.