Compaq Computer Corporation, Inc.

Jeffrey S Watters

James H Nuckols

Norman P Brown

B Tod Cox

Gary L Brasher

Peter J Michels

Michael R Kluth

A computer system having a system ROM comprising a flash or bulk EPROM replacing a block flash or boot block EPROM, and a second ROM to store the primary boot code. In a first embodiment, a single block EPROM is replaced with a bulk EPROM and a ROM, where the ROM is preferably a one-time programmable ROM. The primary boot code is copied into the ROM thereby preventing its erasure. The bulk EPROM is reprogrammed if desired. Separate decode logic detects an address to the primary boot code and enables the ROM. In a second system using a block EPROM and a bulk EPROM as the system ROM, the block EPROM is replaced with a bulk EPROM, and the primary boot code is copied into both bulk EPROMs, preferably at mirrored locations. An external switch is provided with appropriate logic, so that the user may select between either of the bulk EPROMs to boot the system. Thus, if the system is unable to boot from one of the bulk EPROMs, the user may flip the switch to access the primary boot code from the other bulk EPROM. A software program is executed after successful reboot to reprogram and verify the contents of both of the bulk EPROMs. The software reprograms and verifies one bulk EPROM and then reprograms and verifies the other to assure data integrity.

System ROM including a flash EPROM and a ROM for storing primary boot code replacing a block flash EPROM

A data field having a variable number of zero-level bits is read by a bus in a digital system, wherein the bus is pumped by writing all logical 'one' bits onto the bus lines just before they are read. The unused bits will then be still in a logical 'one' state, i.e. a known value, rather than floating or at an indeterminate value. A program for performing this operation in a computer uses steps to prevent other operations such as refresh cycles or interrupts from being interposed between the write and read cycles. A CPU may use this method to read a system identifier value upon boot-up, for example.

Pump bus to avoid indeterminacy in reading variable bit field

A power-on password security function for a digital computer system allows the system software to distinguish between authorized and unauthorized users. Safeguards are made against corruption of password data which could lead to lock-out authorized users, and redundant checks allow the security function to operate even when first-level checks fail. The battery-powered RAM storage area used to hold the password when the system is turned 'off' is protected against being accessible by unauthorized users when the system is turned 'on'.

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Houston, TX, United States of America

Jeffrey S Watters