A computing term, the boot block is a small section of the BIOS flash RAM (usually 4 to 16 kilobytes) that is used to restore the BIOS source code if it becomes corrupted or compromised.

In essence, if your BIOS goes bad, you can:

  1. Turn off your computer;
  2. move a jumper on your motherboard to clear the CMOS memory (you'll have to look up your motherboard for specific instructions);
  3. insert a flash drive (nostalgia alert: or diskette) containing a fresh copy of the BIOS;
  4. Turn the computer back on.

The boot block contains an assembly language program that can read the BIOS and copy it back into the flash memory, thereby fixing your BIOS.

This term is usually referred to in regards to Solaris and other Sun systems, while the term boot sector is generally used for IBM-compatible PCs (although boot sector can also mean the master boot record of a hard disk as well.)

This raises the obvious question: what happens when your boot block is corrupted ...?

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