Feature Extensions for IBM Personal Computer
Original Publication Date: 1984-Jun-01
Included in the Prior Art Database: 2005-Feb-04
New features can be added to a personal computer system without modifying the Read Only Storage (ROS) Basic Input/Output System (BIOS) each time. When new I/O devices are introduced for the IBM Personal Computer (PC), it is desirable to be able to (l) perform a power on test of the feature or (2) allow the new feature to significantly modify the operation of the machine without operator intervention. Here, during the Power On Self Test (POST), the address space from 0C0000H through 0F4000H is searched for a valid ROS module. A ROS is identified with: (1) 55AAH in the first two bytes (2) Length (in 512-byte blocks) in the third byte (3) Valid checksum - i.e., adding together all the bytes of the ROS (from 0 through the length) results in 0.