Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: thedoc on 06/10/2016 19:53:01
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Isaac Lintner asked the Naked Scientists:
How much does the average amount of electric current in a binary 1 weigh?
What do you think?
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In our familiar USB flash drives, the surprising answer is that it doesn't take any electrons to store a "1"; injecting extra electrons into the floating gate of a transistor turns it into a "0".
Having said that, the definition of a "0" or "1" is a somewhat arbitrary choice of the circuit designer.
I could not find a specific number of electrons in a quick search, but it is often possible to recover the correct data even when the wrong number of electrons is present. This is because an error-correcting code is stored with the data, allowing the chip to produce the correct data, even if one cell has totally lost its electronic charge (eg due to a cosmic ray strike, or gradual degradation due to excessive write cycles).
See: https://en.wikipedia.org/wiki/Flash_memory#Floating-gate_transistor
electric current
An electric current implies that the electrons are moving and going somewhere.
Most silicon chip designers try to produce active circuits where the logic level is indicated by the voltage on a wire, rather than the current through the wire. The wires on a chip have a small capacitance, and every time you change the voltage on the wire you must charge or discharge the capacitance of this wire; this draws a current for a small instant, which consumes electric power, and heats up the chip. But once the wire reaches its final voltage, it can stay at a "1" voltage with almost no current, and consuming almost no electrical power, indefinitely.
However, in an unpowered flash drive, the electrons are just passively "sitting there" and not going anywhere, so there is no current.
...unless you take your flash drive with you when you go for a jog!
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Another way to store a "0" or "1" is in a Dynamic Random Access Memory (DRAM). This is the memory used most commonly in desktop computers.
Each memory cell has a capacitance of 25-30 Femto Farads (fF), which can be charged up to perhaps 1V in modern chips.
- This means it contains about 160,000 electrons.
- These weigh about 1.5 x 10-25 kg
Despite the fact that the physical size of DRAM capacitors have declined over many years, increasingly sophisticated methods have been used to keep the actual capacitance fairly constant at 25-30fF. Anything smaller than will have its charge overwritten by alpha particles from natural radioactivity in the environment, or subatomic particles produced by cosmic rays.
See page 24 of: https://www.mitre.org/sites/default/files/pdf/06_1217.pdf