x-memory vs novram


Hello, I want to know if there is some advantage in the x-memory that has not the main memory in a hp41, and also how it compares with a novram module in terms of functionality, I mena, which of this three memory tipes has more advantages, and if the ram in a novram module has some inconvenient versus the x-memory.
Thank you



X-Memory modules are used to extend the adressable

RAM range of an HP-41 to it's full extent.

Due to other (OS addressing) limitations, this RAM will

not be usable asmain memory from the user's point of view,

but instead it will be usable as kinda RAM disc.

Please refer to the suitable manuals,

available either on TOS, or on the hpmuseum CDs.

The NoVRAM module is a module simulator,

and although it has RAM inside the module,

this RAM is used to hold either ROM blocks or other data,

and does not use the main RAM area of the HP-41,

but occupies part of the ROM range,

which is a completely different story.

Please refer to the suitable documents,

available either on TOS, or on the hpmuseum CDs.

To scramble things completely, NoVRAM or a variation of it,

could even be used to emulate X-Memory,

at least if I got the right info from Diego.




so, I want to know if the ram in novram modules can be used to store data and text files and modify them as with the editor or the extended functions or the hepax has some commands to allow do this. I am waiting for the documentation to arrive so I can't still look at it
Thank you


yes to everything: the NoVRAM is a very, very powerful beast...


So the editor ed can be used directly in the ram files, and also manipulate them with the extended functions?
Thank you Ángel


There are effectively 3 types of "memory" modules available for the 41 calculator.
From HP:
Standard -- only for the 41C. These expand the main memory, sometimes refered to as program memory, to the full 319 registers addressed by the 41C firmware. This is the memory the SIZE command lets you divide between programmable and storage registers.
The 41CV and 41CX include these internally so these modules are useless in them.

X-Memory -- this memory is only usable with the X-Functions ROM module. There are two types a X-Function/X-Memory module usable only with the 41C and CV (the 41CX has the X-Function ROM integrated internally) and X-Memory modules with only memory. An X-Memory module in a 41C or 41CV is useless without a X-Function/Memory module present.
HP chose to configure this as a RAM disk, i.e. storage rather than as having the calculator be able to run programs directly in this space. This is basicly due to the origional firmware programming as the CPU can directly address this space and by using synthetic techniques it is possible to run programs stored in this memory.

3rd Party "RAM" modules: These were developed to use ROM module space (the 41's CPU designates seperate spaces for RAM (0-1023) and ROM (4K blocks 0,1,2,3,4,5 reserved for the system and 6-15 for modules) as storage.

NoVRAM memory is technically not RAM. It is non-volitile EEPROM(Electrically Erasable Programable Memory). Diago's excellent module has a microcontroller and EEPROM chips. The microcontroller maps the module's memory into the module memory space.
The advantage to this is that anything in its memory is NOT lost when the module is removed from the calculator. All other memory modules (Standard or XMemory) lose their information when removed.

Diago developed the module as a clone of a module called HEPAX, probably the most advanced 3rd party module developed before the end of the 41 line. HEPAX followed the concept of the X-Functions and came as a HEPAX Function+Memory module and HEPAX MEMORY modules. You always needed the HEPAX Functions code to use its memory. Fully implemented you could have over 2300 registers available of HEPAX memory.

So with a 41CX you could potentially have: 319 registers of "main" memory, 600 registers of XMemory and over 2300 registers of "HEPAX" memory.

The disadvantage is that HEPAX memory reduces the number of modules you can have plugged in as its memory occupies ROM space.

The NoVRAM module is worth much more than simply as memory. With the HEPAX firmware installed HEPAX memory can be divided and a portion used as a ROM module: with User code (ie. programs) and/or firmware (i.e. assembly) stored in it. The HEPAX code can create the Cat2 catalog and entries for user programs which then can be run from that memory just as if they were in a ROM based module. With a knowledge of 41 assembly code the HEPAX editor and utilites allows you to enter assembly routines.
With a PC and external programmer you can use the NoVRAM as like Diago's Clonix and program it with various module's images and run virually any of the modules developed for the 41.

With a PC and programmer the NoVRAM can even be programmed with an extra 8K ROM module as it has extra space even with the HEPAX ROM and full HEPAX memory set up.



Thank you


Excellent summary David, it should go to the forum archives for permanent reference.

Best, ÁM


Dear HP41 NoVRAM enthusiasts :-)

alternatively to the Hepax operating system it is also possible to use the NoVRAM with a RAM-Box operating system. For example the W&W 32Kbyte RAM-Box operating system...

Regards - Christoph Klug


Thank you all for your explanations,
so the question I have now is there seems that there would be no point having any x-memory when you have a novram, or there is any advantage in xmemory overnovram that I am missing?


No advantage to x-memory that I am aware of.

The Hepax functions include "copies" of functions similar to the X-memory functions but that they work on Hepax ram and files.



Dear Fulcrum,

for storing and executing own program code the NoVRAM is a great solution. Because using NoVRAM for executing your user programms you get more free main memory for data. Furthermore with NoVRAM you are able to run really great program applications :-)

X-Memory is a great solution for data storing. For example ASCII text files or special CCD-Module matrix files. I use the X-Memory as data memory for data logging applications.

For an advanced HP41 configuration using both would be the best : A Double X-Memory plus NoVRAM :-))

The W&W RAM-Box operating system also includes commands for data storing to the NoVRAM. Last not least, the special MBK-Profiset RAM-Box operating system includes advanced storing commands for compressed data storage.

Best wishes - Christoph Klug


That is just was thinking myself.
However, the ram with hepax os can store also the registers with hsaver, what gives a great capability of storage, with 16k of "RAM" you can store a lot of programs, data and text files, at least for my use is enough
Thank you and regards


Christoph is (rightfully so) biased toward the Rambox solution, but I should mention that the HEPAX firmware (included into every standard NoVRAM) also provides the capability to store data into the Quasi-RAM area (i.e. the ROM space seen as RAM by it).

Both standard registers and ASCII files can be happilly stored there.. in fact, in my humble opinion the HEPAX solution is every bit as good as the Rambox, and then something better :-)


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