Provided are a method, device, and system for booting from a memory device having an array of blocks of cells. An initial memory map has a mapping of memory addresses to accessible blocks of cells in the memory device that are accessible following a boot sequence. There are secure blocks of cells in addition to the accessible blocks of cells that are not accessible through the memory addresses in the initial memory map. In response to detecting an initialization event, the secure blocks of cells are mapped to a range of memory addresses in the memory map to generate an altered memory map. Code is executed in the secure blocks using the range of memory addresses in the altered memory map. The range of memory addresses mapping to the secure blocks are remapped to map to the accessible blocks to which the range of memory addresses mapped in the initial memory map to restore the initial memory map from the altered memory map.