Apparatus and method for maintaining secured access to relocated plug and play peripheral devices

Abstract

A computer system, bus interface unit, and method are provided for securing certain Plug and Play peripheral devices connected to an ISA bus. Those devices include any device which contains sensitive information or passwords. The device may be encompassed by or interfaced through adapter cards which can be readily inserted into sockets and thereafter relocated to dissimilar sockets. A security device within the bus interface unit keeps track of identifying information of various Plug and Play ISA devices inserted and re-inserted into slots connected to the ISA bus. As a peripheral device or card is moved, an identifying number associated with that device is maintained in a device identification register within the bus interface unit. Moreover, the base address of that device address space is also maintained in I/O address registers contained within the bus interface unit. The device identification registers and I/O address registers are deemed shadowing registers to which future ISA cycles are compared. If an ISA read or write cycle is destined for a secured peripheral device denoted by its shadowed status within the shadowing registers, then securing of that device is achieved regardless of where that device is plugged into a corresponding socket location. In this manner, securable device identification numbers and base addresses can be kept track of (shadowed) such that the shadowing information will purposely mask accesses to relocated ISA Plug and Play secured devices and/or slots.