batteriescellphoneflash
I would like to know how much power does a flash memory chip consume, and whether it is viable for use when the device is switched off since I will require R/W access to the chip when switched off. Device in question is a cell phone, about 2000 mAh.
Is there any other power-saving alternative available other than flash memory? I want the chip to eat only as much power as a cell phone's clock requires, or lesser, since it has to work when switched off as well.
rope data structure
I am fascinated by the rope data structure. I have a hobby project trying to adapt it it to a microcontroller with only a few bytes of RAM hooked to a huge Flash memory, so that I can insert and delete and otherwise arbitrarily edit variable-length text in huge text files. Text files far too large to fit into the RAM. Erasing the last half of the file and re-write it to flash, shifted by one byte, every time I insert or delete a character in the middle of a multi-megabyte text file, would be far too slow, but the rope data structure can do this much faster. Since the rope data structure can represent such mutable random-access variable-length files as immutable fixed-length pieces, it seems to be a good match for flash memory -- all edits are written in a circular-log-like fashion. Alas, all the bugs are not yet worked out in my code. :-(
fixed-length chronological logs
I did get a similar circular log system working, for a product I helped develop.
I simply wrote fixed-length records one after another, filling up flash as a circular array.
(With a completely blank flash, I started writing records about 3 blocks before the end of the array, so I could test the circular wrap-around after only a few records of data were stored, rather than starting at record zero and waiting for a month's worth of data to be written before finding out that there was a bug in my wrap-around code).
I made sure there were always at least 2 erased "erase blocks" ready to be written to. After writing a record, if there was only 2 "erased blocks" after it that were empty, I unconditionally erased the oldest block of data -- the 3rd block of oldest data after the 2 "erased blocks". (Near the end of the flash memory, "after" means "wrap around to the beginning of flash memory). (Perhaps a single erased block would have been adequate -- I forget why I thought I needed at least 2 and sometimes 3).
I forget exactly how many records I put in each "erase block", but I made sure I never had a record straddle two erase blocks -- the first 2 bytes of every erase block of flash was either the "erased" value 0xFFFF, or the first two bytes of a Fletcher-16 checksum (which is never 0xFFFF) in the header of each record.
That made it quick to scan the next time it powered-up and find the head of the circular log -- I only had to look at the first two bytes of each erase block to distinguish between "erased" and "data" blocks. (I was a little worried about "power failure in the middle of erasing a block" causing the first two bytes to be erased to 0xFFFF but leaving non-erased bytes in the middle of the block, so I wrote code for the microcontroller to check for this and restart the "erase a block" process).
Please tell me if you find other flash-friendly data structures or file systems.
EDIT Well with the edited content of the question I'm still a bit confused what you're hoping to get out of an answer. The short and simple answer to your question is "it depends." There is no such thing as "the ideal archival medium."
The fact that you say that "refreshing a flash drive" is a good idea confuses the issue even more. You're asking us to say only based purely on the physics of floating-gate flash technology and GMR storage technology "which is superior." Well, refreshing a flash drive every time that it gets close to it's retention limit doesn't discuss either of those topics and yet it still sounded like what you wanted to hear.
Flash can hold data for a long time in certain conditions and with certain considerations taken into the manufacturing process which sets parameters in how effectively the floating gate retains the charge it is given. To be honest, I'm not in the semiconductor manufacturing field so I can't describe to you what these parameters are. But the problem is that even if I could tell you "flash has a longer retention period if you doped region X with material Y and made this part of the gate larger," that doesn't seem to help anyone produce a system which retains information for longer.
One of the major points of my answer was to show you that the flash technology used in PIC EEPROM and the flash used in a standard SSD and the flash used in a compact flash all have wildly different characteristics. Despite the fact that the intel 520 SSD is a much more modern piece of technology than a PIC, it only guarantees retention for 1 year. It depends on the manufacturing process and without a lot of information about what is even possible within the manufacturing world I can't begin to do math and numbers to try and show you that it's possible to produce an inherently "better" archival medium than a standard HDD.
GMR may or may not be the best way to store magnetic information on a drive when you're optimizing for data retention. The first commercial drive using the technology was only released in 1997, who knows what the real world retention time on these drives is? The ideas behind modern storage are generally aimed at optimizing density which frequently negatively affects retention time. The whole comment about me being unable to find WD specs on data retention periods was also another point: it's not a current concern in the data world how long data can be safely stored.
When it comes right down to it, when you look at the fact that you're looking at timelines in excess of about 10 years, it becomes a bit odd to bother trying to figure out a clever method to do it. Today, you can relatively cheaply hold 3TB of data on a single 3½ inch drive. In 2002 the first harddrive was produced which could hold 137GB. In 1983 the first 3½ inch drive was released with a capacity of 10MB. In 1956, the first drive capable of holding 5MB of data was the size of two refrigerators.
What I'm getting at here is that every problem can be optimized. Why you are optimizing it, what you are willing to do to reach that goal, and what you're trying to accomplish set the parameters for that optimization. I cannot produce different floating gates than what is commercially available now so I did my best to provide some different answers based on what is commercially available now. I cannot make my own harddrives so I did my best to answer with some searching on what's available now. Both of those things are at the mercy of what other people did to optimize, which as previously mentioned was not data retention time, but data density.
Sorry for how long winded that was, but I hope you get what I need to answer the question?
Oh man, this is a question I think about ALL THE TIME. Something I obsess over is duration of media. For some bizarre reason when I was younger I was frustrated by the non-permanence of things, and I sought to find something in which my collection of dumb crap from the internet could last forever. How long are you hoping to archive for? That changes the ballgame completely, but I'll assume the question is for "as long as you can friggin' get it to last."
Note that I also have to ignore the premise of the question because you start getting into extremely dumb scenarios: if you have a set of Samarium-cobalt magnets each the size of a tube of lipstick storing exactly 1 bit (zero is polarized so that north faces one direction through the coil surrounding it and one is polarized the opposite direction), then it will be AWESOME at storing data for an eternity, and I think more effectively than anything you could do with flash, but not very densely packed and extremely expensive.
So to totally sidestep your actual direct question, the best storage medium is probably ink on paper. Not terribly dense, but there are a number of solutions where, if you get a reasonable printer (around 600 dots per inch), and some nice paper, you can fit ~500KB uncompressed on a single 8.5"x11" sheet. Check out this site for an open source implementation. Note that you'll need a scanner which is pretty capable (around 1000dpi non-interlaced) in order to get the data back. I would assume you would want to make it even less dense to get the information to still be readable decades from now.
Back to what exactly you were asking:
Magnetic media has a shelf life of ~10 years before the encoded information is lost because of the continual pull of the Earth's magnetic field. This may be shorter or longer depending on how densely packed the information is, but the rule of thumb 10 years for magnetic data generally holds up well, but I haven't really tried to check it against anything too modern... really, anything within the past 15 years may be worse than this for retention. I know it definitely applies to 5.25" and 3.5" floppy-disks, but modern HDDs are probably much worse. It used to be that the information was encoded as one-bit per magnetically active grain on the surface of the platter in the harddrive. These days, in addition to the grains on the drive being much more fine (and thus more susceptible to external magnetic influence), they also store multiple bits per grain (so north facing up is 00, and north facing down is 11, north to the left is 01 and north to the right is 10, etc). This means that even if they were as resilient as larger grains to the pull of the earth's field, there is a finer line between the states defining the information. That being said, I was unable to find anything from Western Digital which gave a direct shelf-life to the data on it's commercial products.
Flash storage retention gets worse the smaller the flash cell. Currently, the Intel 520 series (the SSD which I own) says that it "meets or exceeds SSD endurance and data retention requirements as specified in the JESD218 specification". Looking up that standard is a pain, so I'll give you the short version: minimum 1 year at 30°C.
So long story short: HDD wins in the density vs time equation. Hands down. The downside is that if you're going for extremely long shelf-life, you'll have to refresh the data periodically (I probably would try and do it once a year), and after a decade or so you'll have to worry about the integrity of the mechanisms inside of a standard hard drive. There are definitely different flash storage technologies, and essentially, the less-dense you're willing to be the longer-lived your data can been retained without migrating. The ultimate (while still being reasonable) archival medium is probably industrial flash technology, but it won't be very dense. See the block below for some more examples of what I'm talking about!
Some other random thoughts:
Best Answer
A flash chip requires power for either read or write access. The power advantage of flash comes from it being non-volatile. That is, it needs no power in order to retain the information on it, once programmed. How much power a flash chip consumes depends on what operation is being called. A write takes about 60 mA at 3 V for up to 3 msec (MLC NAND) That will program a single 16K byte page.
If you do not need large storage density, you can consider PCM memory. It is faster than NAND and byte addressable. For more detailed information go to a memory vendor;s website, such as Micron.com, Samsung.com and look for their publid NAND and PCM memory specifications. these contain information on programming time, read time, how to address them, etc.