CF cards. How do they work?

[mbriant]

Could anyone explain in simple, layman's terms, how exactly Compact Flash Cards, Sony Memory Sticks, etc. work?

How do they store information?

Do they have a power supply?

Will they go "dead" after a long periond of time?

Thanks.

 

[S_Dedalus]

I believe they use a cmos chip, similar to the ROM chips in old macs, but they use far less power and retain data much longer. They use both a negative and positive transistor for each bit. When one of the transistors is switched on, it will read as either a 1 or a 0 for that bit.
They use power from the pci bus.

 

[S_Dedalus]

http://computer.howstuffworks.com/flash-memory.htm
This is a much better explanation than mine

 

[mbriant]

Thanks for the site. There's a lot of info there, but still not exactly what I'm looking for. It's always been my understanding that RAM, ROM, etc. require power to retain the memory. I'm trying to find out what powers a memory card when it's not in a camera, pda, etc.? Does it have some sort of small rechargable battery in it? If so, how long can it store info before it loses it?

 

[S_Dedalus]

When the transistors representing each bit are switched on or off, they remain that way after power is removed, there is no battery involved.

 

[D-EJ915]

They don't require power to retain information, I forgot what type of chip they use unfortunately.

 

[S_Dedalus]

eeprom, which I think is a form of cmos.

 

[mbriant]

Thanks.

 

[lini]

Quote:

Originally Posted by S_Dedalus eeprom, which I think is a form of cmos.

Not quite - eeproms are a bit different and more similar to standard eproms, just that one applies voltage instead of uv light in order to delete the _complete_ content of the chip.

Greetings from Hannover!

Manfred / lini

 

[pedxing]

I wouldn't rely on flash memory for long term storage. I have heard they don't keep data too well for extended periods of time.

Flash memory can only be written to so many times before it fails. San Disk has some whitepapers at their web site describing how they extend the lifespan of their products by shifting the usage pattern of the memory cells.

Do not confuse the micro hard drives with compact flash adapter with compact flash memory.

 

[hongda]

Flash works off of shifting the threshold voltage of the gate of the transistor. Using a water analogy, think of a valve that you use to turn on and off a water spigot. Now the valve is a 0. Put a shim in the valve so now you need to turn the valve less to get the same amount of water out of the spigot. Now the valve with a shim is a 1. Turn off all the water (analagous to turning off the power) the shims stay in place and you retain all the ones and zeroes. To figure out which ones have the shim and which don't, you'll still need to go through turn on the water and turn the valves.