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Why not CMOS?

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Rick Law:
With flash and EE-PROM both have wearing down issue when written frequently, I would imagine CMOS memory module of similar capacity with button battery would be very popular for storing stuff like settings, configurations and such.

Why isn't CMOS memory module over the place?  What is the draw back that I am not aware of?

Cost of the battery, and board space for it.
Need to implement power-fail data protection (if using standard CMOS RAM, which doesn't include that.)

But most importantly, probably the primary reason in corporate minds:
CMOS RAM plus easily replacable, no-leak coin cell, does not meet corporate 'planned obsolescence' objectives. They don't want to sell hardware that users can keep operational forever. They want to make and sell stuff that dies after some years, so the user has to buy a new one.

Limited lifetime flash memory is perfect for that. Since few users can diagnose and replace dead SMD chips. Especially if it held the firmware as well as config data.

Nonsense, the reason is cost, and the fact that battery backed RAM has a battery to fail. It is a common thing for people to modify older equipment to eliminate the battery and replace the memory device with flash or FRAM. Batteries are problematic, a large number of arcade and pinball PCBs have been damaged or destroyed by leaking batteries. Also capacity is a factor, flash chips hold much more data than CMOS SRAM.

Standard flash chips have more than enough endurance for those applications.  Wear just isn't an issue in the vast majority of applications.

In addition to the points james_s makes, replaceable batteries suck if the stored information is important because it gets lost when the battery dies or while you replace it.  If the data is important enough to store maybe it's too important to lose.

David Hess:
Battery backed up CMOS SRAM has been used in various applications in place of EEPROM.  In a low performance design, the CMOS SRAM could even be the main memory for the CPU.  Serial access SRAM is also available which is intended for this sort of application.


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