This allows unsigned ramdisks to be booted. It was first publicized by ZiPhone
Passing pmd*= boot-args specifying a ramdisk in ram > 0x9C000000 allows any ramdisk to be booted.
Credit goes to the Dev Team for the discovery of the ramdisk hack. First publicly released in ZiPhone, using code taken from the Dev Team repository, it allowed running jailbreaks on the fly to be quicker than previous jailbreak implementations, due to the fact that at the time it was the only ramdisk hack jailbreak available.