The Museum of HP Calculators

HP Forum Archive 18

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Message #1 Posted by Keith Beyer on 26 Nov 2008, 8:04 a.m.

I have a really basic question. On an HP 71b, what is the difference between RAM modules and EPROM modules? When searching the 71b listings on that auction site, I see 71b's with RAM modules and some with EPROM modules made by 3rd party manufacturers. What is the difference? Is the EPROM more like a disk to store files/programs?


Message #2 Posted by Marcus von Cube, Germany on 26 Nov 2008, 8:29 a.m.,
in response to message #1 by Keith Beyer

EPROMs are preprogrammed modules which can be erased and reloaded by a special prommer device. They replace ROM modules but are more flexible for the vendor. EPROMs are like modern flash memories but cannot be reprogrammed from the HP71 itself.

RAM is just memory for programs, data and files. A ram module is normally added to to the internal RAM of the machine.

Message #3 Posted by kc7gr on 27 Nov 2008, 11:48 p.m.,
in response to message #1 by Keith Beyer

Perhaps a better way to say it is that an EPROM (Erasable Programmable Read-Only Memory) is a non-volatile storage device that does not require any type of standby power to maintain its contents.

EPROM and FLASH memory are actually fairly different in technology. A typical EPROM requires exposure to shortwave UV light to erase it, and it will only survive a relatively small number of erase/program cycles.

FLASH memory is much closer in function to an EEPROM (Electrically Erasable Programmable Read-Only Memory), with the key difference being that FLASH can be easily erased and rewritten without having to go through the electrical contortions that EEPROMs require. FLASH can also (usually) withstand a much higher number of write cycles before it starts to deteriorate.

RAM (Random Access Memory) is typically volatile, meaning that if the power goes away so does the memory's contents. The big advantage with RAM is that the access time for read and write is far faster than any EPROM or EEPROM.

Scary what I remember, sometimes...

Happy tweaking.


Bruce "What was I saying?" Lane

Ruffler of feathers at inopportune moments

Message #4 Posted by Keith Beyer on 28 Nov 2008, 8:45 p.m.,
in response to message #3 by kc7gr

Thanks very much for the explanations. That was very helpful.


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