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Bit rot in EPROMs

Anonymous Coward

Anonymous Coward

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How common of a problem is this exactly?

Have any of you guys personally had any hardware succumb to bit rot?

Should I be dumping all my old ROMS?
 
It happens, and theoretically will happen to all EPROMs eventually. Most of what you see today tends to be confined to 70's era EPROMs and ROMs.
 
I've certainly had machines come into my possession where the ROM, RAM or ever a logic chip has failed.

As to chips failing when machines have been with me, that's also happened. I try to boot up all my machines regularly (at least once a year) to check them, and sometimes they don't go when previously they have. I've had logic chips fail (in an NEC 8201a and System 80), a Masked ROM fail (I think it was an Apple II+), an EPROM fail (in a PET), a CPU fail (I think on an Apple IIe), a baud generator chip (in a Kaypro II), a keyboard driver chip in an Apple IIe, and a handful of RAM chips. (in an IBMPC, and Apple II+ and an Atari XL).

So, yes it seems to happen. Maybe my place is dangerous place to keep computers! :)

This is why I also give a wry smile when I see that well-used refrain on auction sites "Was going when I last switched it on". Unless it was switched on and tested in the last few days I assume it's not going to go.

Tez
 
How to read old EPROMs in easiest way? Would a cheap usb EPROM burners on ebay work? Do all burners/programmers have the ability to read? Maybe a dumb question, but I have never used one! Have an old 2716 I want to read!
 
I have personally NOT seen an EPROM writer that cannot read an EPROM. Now whether or not it reads the EPROM correctly is a different matter...
We probably should all be making backup copies of EPROMs in our electronics as many of those parts are pushing 30+ years old. I think most were designed for service life of about 10 years.
 
platis said:
Very helpfull, thanks! What is bit rot in detail?
Click to expand...

I understand the term as being the phenomenon where ICs that were ok suddenly stop working after a number of years. However, I've heard it applied to soft media like floppy disks too.

Why do these ICs suddenly fail? Subtle changes in chemical properties over the years I guess?

Tez
 
As I understand it, the data is stored as an electrical charge in the chip and over many years, this charge slowly leaks away until it is no longer possible to read it.
 
...which is why I stated that all EPROMs will experience bit rot eventually. That also includes flash memories--and, in fact, because of the way things are set up (MLC, small geometries), it's doubtful that the data stored in a 64GB flash drive will outlast the 2708 EPROM contents in your old Z80 box. Some old ROMs experience electromigration; I've heard of bipolar PROM fuses regenerating.

Seals fail, charges leak off, things become demagnetized, rubber turns to goo, adhesives don't, lubricants evaporate. Pick your poison.
 
mnbvcxz said:
As I understand it, the data is stored as an electrical charge in the chip and over many years, this charge slowly leaks away until it is no longer possible to read it.
Click to expand...

So couldn't you theoretically refresh them? i.e. if the chip itself is not bad then could you read, wipe, and rewrite the chip every decade or so to prevent the issue?
 
platis said:
How to read old EPROMs in easiest way? Would a cheap usb EPROM burners on ebay work? Do all burners/programmers have the ability to read? Maybe a dumb question, but I have never used one! Have an old 2716 I want to read!
Click to expand...
Depends on what you have available; yes, most if not all programmers can read EPROMS, but some computers also have spare sockets that you could use in a pinch if they're compatible. The later model PETs for example would be able to read a 2716 as is, and many others including PC/XTs and clones should also be able to although they might need a simple adapter.
 
Is it possible to read it thru the parallel port? Write a small program in BASIC to read all the memory locations and list it? A breadboard and some adress decoding circuit! Ok not easiest way, but is it doable?
 
platis said:
Is it possible to read it thru the parallel port? Write a small program in BASIC to read all the memory locations and list it? A breadboard and some adress decoding circuit! Ok not easiest way, but is it doable?
Click to expand...
Absolutely, in fact there are several projects on the Web that do exactly that (as well as some versions that also allow some programming). The usual way is to pulse a pair of cascaded binary counters to step through all the addresses and read the data.

epromr2schem.jpg
 
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