For What?: Two BIOS Chips

It’s for BIOS redundancy and HP SureStart. The backup chip with the clean BIOS is often larger with SureStart dual BIOS setups (Main chip is 128MiB, backup is usually 256MiB). The reason for the backup chip being larger is it holds a “validated” copy of the BIOS for the self healing function, as well as a backup of the current BIOS for quick restoration. The main chip is always smaller, as there is no need for it due to the chip only holding the current BIOS on these machines that use the redundant 256MiB chip with a 128MiB primary.

In my 840 G5, the main chip is 128MiB and the backup is 256MiB and both are made by Winbond. It sounds like HP always uses Winbond for the primary, but uses MXIC as a compatible drop-in. You can tell on Winbond EEPROMs quickly; on mine, the main 128MiB Winbond says 128 in the model and the 256MiB backup says 256 in the model.

SureStart is also why clearing the BIOS takes 10-15 seconds on the HP laptops when you pull the coin cell. It flashes the “known good” BIOS and settings from the backup and just doesn't change the defaults like others do. It's a weird way to do it sure but what if I'm resetting the BIOS I'm already working on it.