Background modes in the ispVM system whether it is Flash or Static RAM (SRAM) are basically to perform functions while the device is running normally, without any interruption.
In Flash Programming Mode internal configuration Flash and SRAM are erased initially and programming is done in the Flash after which the configuration is loaded into SRAM from Flash.
In Flash Background Mode only internal configuration Flash is erased and programmed while SRAM contents are left intact and the device continues to function normally. During next power-on/boot or with a REFRESH command the new configuration is loaded into SRAM from the Configuration Flash. A key benefit to using the background mode is that downtime of the system is minimal. The downtime value can be obtained from the Lattice CPLD datasheets; specified as tREFRESH parameter under "Flash Download Time" table.