DRAM is fast, can be built cheaply to extremely high densities (low $/MB and cm^2/MB), but loses its state unless refreshed very frequently. Its very small size is part of the problem; electrons leak out through thin walls.

SRAM is very fast, less cheap (high $/MB) and less dense, and does not require refreshing, but loses its state once the power is cut. The SRAM construction is used for "NVRAM", which is RAM attached to a small battery. I have some Sega and Nintendo cartridges which have decades-old save states stored in NVRAM.

EEPROM (usually in the form of "Flash") is non-volatile, slow to write, but cheap and dense.

FRAM (ferroelectric RAM) is one of the new generation storage technologies that's becoming available that does what you want: fast, cheap, nonvolatile...but not yet dense. You can get a TI microcontroller that uses it. and delivers the behaviour you want. Cutting power and restoring it allows you to resume where you left off. But it only has 64kbytes of the stuff. Or you could get 2Mbit serial FRAM.

"Memristor" technology is being researched to deliver similar properties to FRAM, but is not yet really a commercial product.

Edit: note that if you have a RAM-persistent system, you either need to work out how to apply updates to it while it's running or accept the need for the occasional restart without losing all your work. There were a number of pre-smartphone PDAs which stored all their data in NVRAM, giving you both instant-on and the potential instant loss of all your data if the battery went flat.

DRAM is fast, can be built cheaply to extremely high densities (low $/MB and cm²/MB), but loses its state unless refreshed very frequently. Its very small size is part of the problem; electrons leak out through thin walls.

SRAM is very fast, less cheap (high $/MB) and less dense, and does not require refreshing, but loses its state once the power is cut. The SRAM construction is used for "NVRAM", which is RAM attached to a small battery. I have some Sega and Nintendo cartridges which have decades-old save states stored in NVRAM.

EEPROM (usually in the form of "Flash") is non-volatile, slow to write, but cheap and dense.

FRAM (ferroelectric RAM) is one of the new generation storage technologies that's becoming available that does what you want: fast, cheap, nonvolatile...but not yet dense. You can get a TI microcontroller that uses it and delivers the behaviour you want. Cutting power and restoring it allows you to resume where you left off. But it only has 64kbytes of the stuff. Or you could get 2Mbit serial FRAM.

"Memristor" technology is being researched to deliver similar properties to FRAM, but is not yet really a commercial product.

Edit: note that if you have a RAM-persistent system, you either need to work out how to apply updates to it while it's running or accept the need for the occasional restart without losing all your work. There were a number of pre-smartphone PDAs which stored all their data in NVRAM, giving you both instant-on and the potential instant loss of all your data if the battery went flat.

DRAM is fast, can be built cheaply to extremely high densities (low $/MB and cm^2/MB), but loses its state unless refreshed very frequently. Its very small size is part of the problem; electrons leak out through thin walls.

SRAM is very fast, less cheap (high $/MB) and less dense, and does not require refreshing, but loses its state once the power is cut. The SRAM construction is used for "NVRAM", which is RAM attached to a small battery. I have some Sega and Nintendo cartridges which have decades-old save states stored in NVRAM.

EEPROM (usually in the form of "Flash") is non-volatile, slow to write, but cheap and dense.

FRAM (ferroelectric RAM) is one of the new generation storage technologies that's becoming available that does what you want: fast, cheap, nonvolatile  ... but not yet dense. You can get a TI microcontroller that uses it: http://www.ti.com/lsds/ti/microcontroller/16-bit_msp430/fram/overview.page?DCMP=FRAM&HQS=fram and delivers the behaviour you want. Cutting power and restoring it allows you to resume where you left off. But it only has 64kbytes of the stuff. Or you could get 2Mbit serial FRAM: http://www.fujitsu.com/global/services/microelectronics/product/memory/fram/standalone/1m-2m-spi.html

"Memristor" technology is being researched to deliver similar properties to FRAM, but is not yet really a commercial product.

Edit: note that if you have a RAM-persistent system, you either need to work out how to apply updates to it while it's running or accept the need for the occasional restart without losing all your work. There were a number of pre-smartphone PDAs which stored all their data in NVRAM, giving you both instant-on and the potential instant loss of all your data if the battery went flat.

DRAM is fast, can be built cheaply to extremely high densities (low $/MB and cm^2/MB), but loses its state unless refreshed very frequently. Its very small size is part of the problem; electrons leak out through thin walls.

SRAM is very fast, less cheap (high $/MB) and less dense, and does not require refreshing, but loses its state once the power is cut. The SRAM construction is used for "NVRAM", which is RAM attached to a small battery. I have some Sega and Nintendo cartridges which have decades-old save states stored in NVRAM.

EEPROM (usually in the form of "Flash") is non-volatile, slow to write, but cheap and dense.

FRAM (ferroelectric RAM) is one of the new generation storage technologies that's becoming available that does what you want: fast, cheap, nonvolatile...but not yet dense. You can get a TI microcontroller that uses it. and delivers the behaviour you want. Cutting power and restoring it allows you to resume where you left off. But it only has 64kbytes of the stuff. Or you could get 2Mbit serial FRAM.

"Memristor" technology is being researched to deliver similar properties to FRAM, but is not yet really a commercial product.

Edit: note that if you have a RAM-persistent system, you either need to work out how to apply updates to it while it's running or accept the need for the occasional restart without losing all your work. There were a number of pre-smartphone PDAs which stored all their data in NVRAM, giving you both instant-on and the potential instant loss of all your data if the battery went flat.