Expensive Dual X-Memory

Maybe this is just my imagination, but isn't this an extremely high price for this module?

Dual X-Memory module sold for $380

I haven't seen too many of these being sold, but this seems awfully high. What do you think?



the double X-Memory pack does not add 600 X-registers. EMROOM, an X-function available only in the HP41CX (the closest X-Function that returns free room in X-Memory is EMDIR), will show 600 X-registers ONLY, not an additonal amount. There are 124 already built in the X-Functions-memory module. Each X-Memory adds 238 registers, the double adds 476, and final count reaches 600.

Maybe the seller was not aware of what he wrote. Or it's a classical "I'm not sure about how to use it" case.

Oops! I feel flames and blames around...


Hi Luiz,

You are correct that his description is not precise, but what he is selling is an X-Memory module that has been modified by someone (don't know if HP ever sold it that way) to include the equivalent of two "normal" X-Memory modules. So, when you plug it into a 41CX (or a C or CV with X-Functions module) the total will be 600 registers. So it is unique in the fact that it is two modules in one.

Still, $380? I'm just amazed.


Saw it. I was willing to go basically double what a single xmem rom went for, but $380.00 was incredible. WOW!!


that's about $119,000/MB!



Lets see, with a little luck you can snag an XMEM for $25 bucks or so. Double that and spend about 30 minutes with pry bar and a soldering iron... voila... about $300 profit.


Hi, Dave.

What you mention is 100% correct. And I remember reading that EduCalc had this sort of double X-Mem for sale (one of our recent contributors has one of this, and he recently repaired his HP41CX and now he can use it... Lucky friend, isn't he?).

What I actually mean is that the double X-Memory will effectively add 476 registers, and the seller claims it will show an addition of 600, what's wrong. Well, he has already sold the module, what else to say?

I have two X-Memory and I use each of them separately, one in an HP41CX and the other in a CV with X-Functions. Plugging them both in any of them allows me to read [600.0000 ] in the display after a EMDIR (or EMROOM in the CX). And they both together are the same as one double X-mem.

I'd like also to mention that the Double X-mem buyer spent a significant amount of money... I paid about US$ 80,00 for both X-Memory, thanks to a friend that was surely interested on seeing me with them, no profits at all.

Best regards.

Luiz C. Vieira


Colleagues - Years ago I sent my HP-41C Quad Memory Module to EduCalc to have it combined with an X-Functions and X-Memory module (a tripple!), and then later, I bought one of EduCalc's offerings of a 2X X-Memory module (a double). As I recall, they cost around $225 for the triple and $200 for the double.


Richard W. Smith


How about it? I'm sure you'd have some fellow collectors who'd be VERY happy with you.




And if someone is creative enough to bring out the
soldering iron, he might as well go the whole way and
build them into the calculator, and thus free up two
ports, instead of just one.


Does anyone know how to connect internally two x-memory modules?



I'm asking about this because I believe taht soldering an external module inside an HP41 will give us a "pack" of things (stuffs?) that became unstable. Yes, you know that soldering X-MOS (X = N, C, V...) is something to be avoided at all costs, even with the safest soldering equipment... mostly if the equipment being soldered has no replacement parts.

I prefer haveing my external modules and, the least as possible, trading them with stable, unchanged HP41's. I use two X-Memory and they are normally in two different calculators. The one mosule I'd like to have a pair (or spare) is the HPIL, because with it I can transfer files and there will be seldon situations where I'd need to trade modules for running programs. At least not so specialized programs.

What I believe is fair is the multiple ROM modules. As some of us have access to ROM images that are only usefull in the HP41 or in an HP41 EMU, these ROM images could be built inside one single module. One of our regular contributors was working on this subject a sometime ago (about a year) and the last new was that hes HP41 was able to communicate with the custom module.

I'm not sure I would wire-up some modules inside one of my HP41's, but I have two HP82106A (regular memory module) and I would open one of them to trade its "guts" for a quad ROM with, say, a CCD, a PANAME, a PPC and an Advantage image at once... What? Can't I dare dreaming?


Luiz C. Vieira (Brazil)


Good idea? Well, if you are soldiering two X-MEM
together anyway, you are already "breaking" them up.
Personally I don't consider X-MEMs that moveable.
Unless you take great care, or move them together with
an X-FUNC, things will not work out nice anyhow.

I did build in two X-MEM in my CX, along with the ZENROM,
but this was about 15 years ago now.

Yes, it works, have been working fine all the time, and
no, there are no big dangers in doing so.

The ZENROM was explicitly designed for building in to
your HP-41, by the way. Preferrably at the same slot as
the magnetic card reader.


Until now I thought that my $71.81 for a dual X-memory and math/stat module (3 in 1) were not so cheap...

I made a deal, after all!




Back in the good old days I used to double (and on one or two occasions even triple) modules, or build them inside an HP41 for friends (for a nominal charge), typically in combination with a speed-up. This is not really a very big deal, you need a steady hand. Dangerous part is actually in cutting the modules. I still have some stock of empty module housings with connectors (no, I will NOT give them away!)

A few pictures are in my museum at www.kuipers.to/hp41 where you can see inside my HP41C with Quad MEM and TIME built in. Getting in more will be difficult. Just use thin wires and pick the right traces. I anyone is interested, I can make better pictures. Just mail me!

The biggest trick was always to build a tantalum cap in an XFUN/XMEM combination. That would hold the contents for several minutes, enough at least to hand the module to a friend and have him copy the contents. This obviously only works when XFUN is not built-in. The first picture in my gallery actually shows a XFUN/XMEM combination with the tantalum cap!



I have a dual X-Memory that was modified by EduCALC. If I thought I could sell it for that price, I would have to, just to suprise my wife wityh some extra cash.

In college I doubled a couple of modules for myself. I admit it would be harder to solder now, my 20-20 vision is more like 25-20 or 30-20, but it could still be done.

If there is much interest, I could locate the "Butcher lock" columns out of the PPC Journals and post them as an Adobe PDF.


"Butcher lock" columns ???
I'm really interested to hw modifications... Let me know...


Yes i'm lucky :-) I had this module and didn't know the use for it since Luiz told me how to get it! the Double x-memory from educalc is also written "module service" but i don'tknow what it this use. Luiz is right : this module add to the existent x-memory up to 600 Reg.

So the price is very high for 2 x-memory in one module... Perhaps i should sell my module and buy 2 normal x-memory modules AND another HP-41CX, advantage module, math/stat with the extra money... :-)))


I support you, my friend.

(I'm preparing some stuff about your e-mail question and I'm sending it as soon as I have id ready, O.K.?)

Best regards.


Hi X-Memory enthusiasts,

I build a double X-Memory module and described the complete procedere in Chapter XII of the nice I/O-Board manual (300 interesting pages about HP41 hardware interfacing and measurement applications).

If possible I will place Chapter XII to the HP-Museum articles forum.

Best wishes from Germany - Christoph Klug


Hi all of you 41'ers

Yeah! HW makes my life go round!

Gimme something I can use an soldering iron on (or, even better, "in") and you'll make me happy.

Ok, I'll stop kidding...

When I first get a Quad for my 41C (back in the 80's) it goes almost directly inside the calc. I didn't solder it, (the internall appearence of my old fullnut seems so impressive to me that the mere idea of a solder stain in such a beautifully engineered "golden lines pattern" makes me feel sick) instead of that I built a "thin wire conector" and placed it between the I/O connector block and the keyboard PCB, thus the contact was made when the two halves were tighten back together.

It was running this way for years... up to the day CuSO4 started to "eat" the contacts (forgotten batteries: my fault) and I had to turn the Quad back to its plastic box... But this is another story.

You can place modules inside your 41 using this concept, I think it's much safer than messing with solder.

If there are any other(s) HW nuts over there (I guess they are) interested in the process I'm glad to offer my little support and knowledges.

Bye from the Canaries.


P.D. Please excuse my English "crimes" :-)


It might also be wise here to point out that
most "normal" modules cannot be built together.
"Normal" modules occupy memory in the processors
memory space. The processor can address 64K.
Each port has a designated 8K range allocated to
it. If you put several modules together, they will
occupy the same memory range, and won't work.
Memory modules work in a different way, and therefore
can be built together in other ways.

The ZENROM is a special case because it's only 4K.
Normally, 4K modules use the lower 4K of a ports memory
space. However, the ZENROM occupies the high 4K.
And therefore, you can combine it with any other
module, which only uses the low 4K.
The magnetic card reader is such a module, and therefore
it's perfect to build in on the same port as where
the card reader is.


When I build in my ZENROM and two X-MEM, I removed
them from their modules. The "chips" are small squares.
I placed them in the small space along the sides inside
the calculator, and used wire wrap gauge to attach
them to the normal I/O connectors, just as if they
had been inserted into the calc.
I soldered those wires, but solering on the I/O
connectors wasn't that bad or dangerous.
And normal modules can still be inserted. The inner
edge of the connectors are slightly "fatter", but that
have not been any problem with any modules.

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