Unsolvable problems in CS

Conundrum, Thu Apr 27 2017, 07:27AM



I solved this a long time ago, seems that the "trick" was to exploit the randomness present in RAM at the time.
Essentially an older generation (16MB) memory chip can store far more data because each cell has many more analogue levels than are normally used so a sufficiently well designed system can map these out using a lookup table to subtract the right values from each cell and recover the original video file with the TV itself helping to play back a degraded video stream.
As long as power is continuously provided and the chip is kept within a narrow temperature range to reduce entropy, it can store 4-6* as much data with exponentially increasing error rates at higher values.
This is incidentally how it is possible to extract encryption keys from turned-off PCs, the special kit freezes memory and allows a few minutes to quickly dismantle the machine and plug it into the special reader.
There will often be errors but it reduces keyspace by several orders of magnitude allowing a graphics card array to do the pattern matching and recover the original keyfile.

A few years back I came up with the same idea but using strontium titanate (SrTiO3) on a-Si based analogue storage (eg ISD1xxx) ICs used in some digital greetings cards. My original plan was to use them to store SSTV signals but ran into the limitations mentioned earlier ie there is no way to easily correct cell variations so there will always be a lot of noise present.
A conventional VCR or even tape deck run faster than usual is far better or my later invention of the "optical persistence memory" based on stimulated fluorescence in ZnS:Cu with data written and read using infra-red, UV and red SMD LEDs with micro-lenses imprinted using light cured glue around late 2009.
The array is looped so that data is constantly corrected and re-written during copying and thus the module can verifiably and securely store data for weeks at a time using less power than a conventional SSD with no possibility of recovery if power is interrupted even for a second.

Technology has moved on a lot since then, 2GB of fast digital storage is pence now.

Its a shame that you can't buy these chips any more, the original ones were much better but the newer ones are value engineered and even noisier due to cheaper materials/smaller feature size.

EDIT many newer flash memory chips use an approach like this but using an area compensation method at chip level, so that the data in each "zone" determines overall levels. This is also how wear leveling works so well because adjacent cells are typically fine.