Abstract: A computer system has a plurality of processing units (2-1,2-2,2-n) connected via one or more system buses (1-1,1-2). Each processing unit (2-1,2-2,2-n) has three or more processors (20-1,20-2,20-3) on a common support board (PL) and controlled by a common clock unit (1000). The three processors (20-1,20-2,20-3) perform the same operation and a fault in a processor (20-1,20-2, 20-3) is detected by comparison of the operations of the three processors (20-1,20-2,20-3). If one processor (20-1,20-2,20-3) fails, the operation can continue in the other two processors (20-1,20-2,20-3) of the processing unit (2-1,2-2,2-n), at least temporarily, before replacement of the entire processing unit (2-1,2-2, 2-n). Furthermore, the processing unit (2-1,2-2,2-n) may have a plurality of clocks (A,B) within the clock unit (1000), with a switching arrangement so that the processors (20-1,20-2,20-n) normally receive clock pulses from a main clock (A), but receive pulses from an auxiliary clock (B) if the main clock (A) fails.

Abstract: A computer system has a plurality of processing units connected via one or more system buses. Each processing unit has three or more processors on a common support board (PL) and controlled by a common clock unit. The three processors perform the same operation and a fault in a processor is detected by comparison of the operations of the three processors. If one processor fails, the operation can continue in the other two processors of the processing unit, at least temporarily, before replacement of the entire processing unit. Furthermore, the processing unit may have a plurality of clocks (A,B) within the clock unit, with a switching arrangement so that the processors normally receive clock pulses from a main clock (A), but receive pulses from an auxiliary clock (B) if the main clock (A) fails. Switching between the main and auxiliary clock (A,B) involves comparison of the pulse duration from the clocks (A,B).

Abstract: A program replacing method is provided for an uninterruptible online computer system. The computer system includes an auxiliary storage unit for storing a program currently running in the computer system and another program to replace the current running program and a replacement request managing table for storing replacement requests and program IDs of such replacing programs. These programs include checkpoints pre-programmed at selected locations therein. At an optional checkpoint, the replacement request managing table is retrieved for checking whether or not the replacement is requested. If a replacement is requested, the new program is started according to the program ID and the current program is terminated.