Computer system with program loading apparatus and loading method

An apparatus and method for loading BIOS from a diskette drive (66) into a personal computer system (10) normally connected to a fixed disk drive (62). The personal computer system (10) further includes a system processor (26), a random access main memory, a read only memory (36) and a switching means. The switching means generates a signal to indicate a mode for whether BIOS loads from either diskette or disk. In a priority mode, BIOS loads immediately from diskette. In a recovery mode, BIOS loads from diskette after testing the disk subsystem. The read only memory (36) includes a first portion of BIOS and data representing the type of system processor (26) and system planar (24) I/O configuration. The first portion of BIOS initializes the system (10) and queries the switching means. If the fixed disk is not available or the master boot record on the disk is invalid, the first portion of BIOS reads in a master boot record from the diskette drive (66). For either mode, the master boot record includes a data segment (122-138) and an executable code segment (120). The data segment (122-138) includes data representing system hardware and a system configuration which is supported by the master boot record. The first BIOS portion transfers control to the executable code segment (120) which confirms the master boot record is compatible with the system hardware by verifying that the data from the data segment (122-138) of the master boot record agrees with the system processor (26), system planar (24), and planar I/O configuration. If the master boot record is compatible with the system hardware, the executable code segment (120) confirms that the system configuration has not changed and loads in the remaining BIOS portion from the diskette drive (66) into random access memory (32). The executable code segment (120) then verifies the authenticity of the remaining BIOS portion and vectors the system processor (26) to begin executing the BIOS now in random access memory (32). BIOS, executing in random access memory (32), then boots up the operating system to begin operation of the personal computer system (10).