SRAM stands for Static Random Access Memory. The SRAM cell has two cross coupled inverters and uses a standard CMOS process. "The Configuration cell drives the gates of other transistors on the chip-either turning pass transistors or transmission gates on to make a connection or off to break a connection."
In the case of SRAM, designers can use the the chip again at prototyping and the system can be manufactured using ISP. This way a new configuration can be sent instead of sending a totally new chip. System can be updated or changed in real time.
The power needs to be continously supplied to the programmable ASIC for the volatile SRAM to retain the connection information. The configuration DATA can also be loaded from a permanently programmed memory(PROM) every time the system is turned on.