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Perhaps this question may sound silly,and am sorry if there are similar questions answered already because i couldn't find one, as per guidelines. Mask ROM(MROM) are programmed while manufacturing,PROM can be programmed after manufacture and same follows to EPROM and EEPROM similarly how are ROM's are programmed. I assume ROM and MROM are two different things,latter one with program in it loaded while manufacturing. Also if i have wrong concept in my head please make it clear.

Samdare
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  • what is a normal ROM? – jsotola Mar 29 '18 at 19:23
  • as per edited question @jsotola – Samdare Mar 29 '18 at 19:28
  • ROM describes single behaviour of a memory but that can be manufactured by a variety of technologies (processes). (These names often spark enthusiastic and well-meaning but pernicketty discussions with no end because it's hard to put everyone's 'I know it when I see it' definitions into a single absolute term...) – TonyM Mar 29 '18 at 19:34
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    See https://electronics.stackexchange.com/questions/243712/eeprom-is-a-read-only-memory-so-why-can-i-write-to-it/243725#243725. – Transistor Mar 29 '18 at 19:36
  • The "rope" ROM in the Apollo guidance computer was progrmmed using a needle to thread wires through transformer cores. – Jasen Слава Україні Mar 29 '18 at 21:10
  • @Jasen: I think that would be "core memory". That was used as RAM at that time, but it was non-volatile, so it could also be used where ROM would have been used. – Peter Bennett Mar 29 '18 at 22:04
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    @PeterBennett no they were not RAM cores in the rope ROM, just ransformer cores. the data was represented by the routing of the address wires through the data cores. https://en.wikipedia.org/wiki/Core_rope_memory – Jasen Слава Україні Mar 29 '18 at 22:07
  • Although your "MROM" does make sense, I don't think it was ever used. When mask ROM was first used, it was the only sort of ROM available, so there was no need to add the "M". The term "ROM" has since become a general term for any sort of read-only memory. – Peter Bennett Mar 29 '18 at 22:07

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I assume ROM and MROM are two different things

You assume incorrectly. "ROM" is just an umbrella term that can be used to refer to any type of memory that cannot be modified after the device has been manufactured. If not otherwise specified, it usually refers to mask ROM, but it can also refer to other technologies which behave the same way, like PROM/EPROM devices or flash memory with writes disabled.

  • I think you mean 'cannot be modified by software'. The end user of an embedded system, such as a vending machine, cannot modify the ROM or anything else in its CPU system. – TonyM Mar 29 '18 at 20:01
  • @TonyM I mean the end user of the part, not of the device it's used in. A microcontroller may have a boot ROM which is implemented as flash, but is made non-writable before delivery to the "user" of the µC. –  Mar 29 '18 at 20:13
  • Would be good to clarify that in your answer. There's only one end user in anything: the user of the final product. Follows that I should downvote, I'm afraid, will remove once terminology clarified. – TonyM Mar 29 '18 at 20:24
  • I might say that "ROM" is any sort of memory that cannot be written to using a normal processor "write" cycle. – Peter Bennett Mar 29 '18 at 22:11
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    @PeterBennett That's probably too broad. NAND flash memory would be swept up by that definition, for instance.. –  Mar 29 '18 at 22:14
  • if you substitute rewritten for written nand flash is excluded, and writing flash usually more than a normal RAM write. – Jasen Слава Україні Mar 29 '18 at 22:20
  • @duskwuff: If one wants to divide read-addressable memories into "RAM" and "everything else", I'd say a defining characteristic of RAM is that they can be written, in addressable fashion, an arbitrary number of times. If one wants to divide memories into "ROM" and "everything else", I'd draw the distinction based upon whether they hold contents without power, and whether they would be non-writable in a target application circuit. Some chips might be only usable as RAM, others only as RAM, some only as a "something else", and some as all three, depending upon the application. – supercat Mar 29 '18 at 22:29