NOR, Where Art Thou?

[Jon Westfall]

<div class='os_post_top_link'><a href='http://blogs.msdn.com/windowsmobile/archive/2006/06/19/637638.aspx' target='_blank'>http://blogs.msdn.com/windowsmobile.../19/637638.aspx</a><br /><br /></div><i>"I've been asked why OEMs would use NOR flash in a persistent storage world. (If words like "NOR flash" or "XIP" are confusing, read this.) I'm going to give you some history about where NOR flash came from, explain how we got from there to here, and prognosticate a bit on the future. The first PocketPC to have any sort of embedded flash memory was the original iPaq (it was released in 2000). Before that, all our devices shipped on what was known as "Mask ROMs." A Mask ROM is created at the factory and can't ever be erased or changed. Obviously, we never stored user data in these (there was no way to write them), and the only way to ever "upgrade" a device with a Mask ROM was to physically remove the chip and put a new one in. (Yes, I'm ignoring EEPROMs. They were using during development, but few, if any, devices were shipped to customers with them.) It's important to note that code in Mask ROMs could be executed in place. That is to say, they XIPed. Now, NAND flash had been around for a long time. Those old Mask ROM PDAs had CF slots, and the CF cards were made of NAND-based Flash memory (frequently called Flash ROM even though that's not technically correct). NAND, however, can't XIP, so it couldn't be used as a direct replacement for Mask ROMs. "</i><br /><br />For those of you chip junkies out there that wondered why NOR hasn't been used much in our devices, check out this excellent post on the Windows Mobile Team Blog!

[sapibobo]

What type of ROM HX4700 is using? Any info? Thanks

[inteller]

I could have sworn that my olf HP320LX ROM "upgrade" required me to pull out one chip and insert another to go from CE 1 to CE 2.0 Would that not have been a mask ROM?

[Horus]

I could have sworn that my olf HP320LX ROM "upgrade" required me to pull out one chip and insert another to go from CE 1 to CE 2.0 Would that not have been a mask ROM?
Yes. Mike mentions this in his blog post. Because it was mask ROM, you had to change the chip.

[inteller]

I could have sworn that my olf HP320LX ROM "upgrade" required me to pull out one chip and insert another to go from CE 1 to CE 2.0 Would that not have been a mask ROM?
Yes. Mike mentions this in his blog post. Because it was mask ROM, you had to change the chip.


ah nevermind, I got lost in all those commas and parentheses he was talking about EEPROMS never being used.

[davea0511]

Nice summary. The question is when will MRAM, FRAM, or OUM start replacing these - and which will do it? My guess is MRAM for the XIP, and OUM for persistent storage. Probably another 5-10 years out.

I still think they need to massively parrallel the RAM with a flash chip that has massive multiplexing so when you're not using the PDA the RAM instantly copies all it's contents to non-volatile memory and then powers off completely. That's similar to what the NAND / RAM chips do today, but the NAND doesn't mirror the whole RAM, and as fast as NAND is, it isn't multiplexed enough to provide that high of bandwidth when writing.