Path: news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail
From: Rich <rich@example.invalid>
Newsgroups: comp.os.linux.misc
Subject: Re: FAA To Finally Ditch Floppy Disks & Win-95
Date: Sun, 15 Jun 2025 14:04:00 -0000 (UTC)
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c186282 <c186282@nnada.net> wrote:
> On 6/14/25 7:38 PM, The Natural Philosopher wrote:
>> On 14/06/2025 17:34, Rich wrote:
>>> Also because (esp.  for EPROMS) the rope memory was much more 
>>> radiation hardened than EPROMS of the day were.  Also, for 'long 
>>> duration' projects such as that, often each component is designed 
>>> and built, then in the end the various parts are pieced together to 
>>> produce the "flying candle" you see on launch.  But the "computer" 
>>> might have been designed and built five years before that launch, 
>>> and minus five years from today might have meant no PROM or EPROMS 
>>> were even available at the time.
>>>
>> There is another issue I ran into.  On an undersea cable repeater.  
>> IN 1988 or thereabouts the company was overjoyed to finally be able 
>> to use silicon, because up till the early 80s silicon simply hadn't 
>> been around long enough to be deemed suitable for long term use 
>> (>25yrs).
>> 
>> Rope memory was tried and tested, Fusible link PROMS had no track 
>> record and EEPROMS were definitely subject to ageing
> 
>   I'd argue that fuse PROMS didn't NEED a 'track record'
>   because they're SO straight-up.

While true, that's just not how getting things in space work.  They 
have to be exposed to the radiation environment they will see in space, 
and their success/failure determined from those tests.  I.e., they have 
to have a "track record".

>   UV-EPROMS are also pretty stable (and NOT nearly so sensitive as 
>   some here suggest).

Stable here on the surface, where we are shielded from almost all of 
the space radiation.  But UV-EPROMS work on the same principle as flash 
(a charged, insulated, floating gate stores the bits).  UV erases them 
because the UV radiation is energetic enouogh to cause the charge to 
drain from the floating gates.  Well, guess what, there's lots of 
radiation in space that is far more energetic than UV radiation, so 
your UV EEPROM will likely lose its stored program (either in short 
order, or well before the service lifetime of the satelite it is 
installed into).  Both of which make it unsuitable.

>   EEPROM was more complicated.  Most Flash is even more suspect.

The only real difference between the UV model and the EE/flash models is 
the EE/flash models don't need UV light to initiate the discharge of 
the floating gates.  But the mechanism of storage is the same in all of 
them.