First Data Change Detection
Original Publication Date: 1987-Apr-01
Included in the Prior Art Database: 2005-Feb-01
This invention detects and signals the first attempt to change a main store page and prevents changes to the page until the unaltered page can be processed. This is accomplished through changes to the central processing unit (CPU) hardware, horizontal microcode (HMC) and by adding an additional indicator to each primary directory entry and lookaside buffer entry. On the IBM System/38, internal-microprogram instructions use virtual addresses which must be translated to resolved main store addresses before the addressed page can be accessed. A primary directory (PD) maps virtual to resolved addresses. A lookaside buffer (LB) is a partial copy of the PD containing portions of recently used PD entries. The CPU hardware performs translations using the LB.