The switch modules that were installed on the chassis when the standby MM was once primary. The time of the last update can be obtained by querying rbistUpdateTimePrimary object. The switch modules are listed as a bitmap. The bitmap is a string containing a list of 1's and 0's that is as long as the number of switch modules supported. If a switch module was installed in a bay, a 1 is present in the string in the position representing the bay ID as read from left to right. For example, if switch modules were installed in bays 1 and 3, and 4 switch modules were supported, the string would look like '1011' for BladeCenter and BladeCenter T and '1011000000' for BladeCenter H and BladeCenter HT.