It became a national holiday in 1948, but it has been a day of celebration in Japan since ancient times. The fifth day of the fifth month was traditionally called Tango no Sekku and was a festival for boys. Girls have their own festival, called Hina Matsuri (Doll Festival), held on the third day of the third month.
Expressions full disk encryption (FDE) or whole disk encryption signify that everything on disk is encrypted, but the master boot record (MBR), or similar area of a bootable disk, with code that starts the operating system loading sequence, is not encrypted.
Full disk encryption for the boot disk has the issue that you have to decrypt the blocks where the operating system is before you boot the OS (i.e. before you load Windows, for example) meaning that the key has to be available before there is a user interface to ask for a password.