There are four main things called memory in Android.Simplified1 Ram. Real memory where code is loaded and executed speed measured in normally matched to the CPU Mhz/Gmz. the low end slates are 128Meg/256Meg info in RAM is lost at power off.2. internal Memory. like a C: drive in windows. long term storage of the OS and App storage. speed is measured in class/MBper sec Most devices have 1gig+ Some mother boards this is a internal microSD slot and is sold with different size microSD cards preinstalled. it is simple to open and replace with faster/larger microSD. Data retained when power is turned off3. SDcard Normally, a slot SD or MicroSD user supplies this card and more than one can be used. speed is measured in class/MBper sec My design data storage only. in 2.2 limited support for installing apps. place to store pictures,music, apk (file to install app) etc. Data retained when power is turned off4. USB Some devices have drivers that support a thumbdrive can be used like a second SDcard. Can copy to/from sdcard, store misic video etc. Data retained when power is turned offYou can't use SDcard type memory as RAM.But the android RAM memory manger can use a 'SWAP" drive. Some custom roms allow you to partition a small 96-128meg section of the SDcard and make a swap area.So code in ram not used recently is swapped to the swap drive, effectively giving you more RAM.