A computer system in a fault-tolerant configuration employees multiple identical CPUs executing the same instruction stream, with multiple, identical memory modules in the address space of the CPUs storing duplicates of the same data. The system detects faults in the CPUs and memory modules, and places a faulty unit offline while continuing to operate using the good units. The faulty unit can be replaced and reintegrated into the system without shutdown. The multiple CPUs are loosely synchronized, as by detecting events such as memory references and stalling any CPU ahead of others until all execute the function simultaneously; interrupts can be synchronized by ensuring that all CPUs implement the interrupt at the same point in their instruction stream. Memory references via the separate CPU-to-memory busses are voted at the three separate ports of each of the memory modules. I/O functions are implemented using two identical I/O busses, each of which is separately coupled to only one of the memory modules. A number of I/O processors are coupled to both I/O busses. I/O devices are accessed through a pair of identical (redundant) I/O processors, but only one is designated to actively control a given device; in case of failure of one I/O processor, however, an I/O device can be accessed by the other one without system shutdown.

Fault-tolerant computer system with online recovery and reintegration of redundant components

A method and system for remotely accessing and controlling at least one of a target switch and a target computer using a target controller. The video information captured by the target controller is analyzed and compressed in order to reduce network traffic between the target controller and a controlling computer.

Method and system for intelligently controlling a remotely located computer

A system and method for accessing, controlling and monitoring a data processing device in which a video raster signal from the data processing device is analyzed to determine the information displayed on a video display monitor attached to the data processing device is used. The video raster signal is converted to a digital form and a cyclic redundancy check is performed on the digital data to determine the information contained in the video raster signal and to generate a compressed representation of that information. The information may then easily and quickly be transmitted to a remote location for analysis and review. Additionally, commands from the remote location can be transmitted to the system to control the data processing device.

System and method for remote monitoring and operation of personal computers

A system and method for maintaining logically consistent backups using minimal data transfer are presented A system comprises a backup system having a backup storage device and one or more primary systems having mass storage devices that are to be backed up on the backup storage device The primary systems identify changes that are going to be made to the mass storage device The combined effected locations in the mass storage device of these identified changes are then captured in a static snapshot when the mass storage device is in a logically consistent state Only those data blocks changed since the last backup are then transferred to backup system The backup system can then store these changes or apply the changes to the backup storage device in order to bring the backup storage device current to a particular point in time

Backup system that takes a snapshot of the locations in a mass storage device that has been identified for updating prior to updating

A fault tolerant multiple network server system in which multiple servers concurrently act as back-up servers for each other even while they are providing their own server services to the system. Rather than having an unused server monitoring for failure of a primary server and taking over control, each is act upon the network, but when its partner should fail, it assumes control of these partner servers storage subsystem. In this way, processing power of both servers is available during normal operation, but they each provide back-up capability for the other.

Fault tolerant multiple network servers

A is a duel processor system (100) with duplicated memory (114,124) has two modes (10,11) of operation: a converged mode (10) in which one of the two processors (101,102) is active and executing all system tasks while the other processor is inactive; and a diverged mode (11) in which both processors are active and independently executing different tasks. The system automatically changes modes in response to requests such as manual and program control and certain system fault conditions. In diverged mode, the system may be in either of two states of operation (1 and 2). In one state (1) one processor (101) is designated a primary processor, and in the other state (2) the other processor (102) is designated the primary processor. In the converged mode the system may be in either of four states of operaton (3-6). In two of these states (3,4) one processor is active while the other processor is standing by ready to take up execution of tasks from the point where the one processor stoped execution. In the other two of these states (5,6) one processor is active while the other processor is out of service and cannot take up task execution without being initialized. The system 100 makes transitions between the various states in response to requests. Except for transitions of an active processor to an out-of-service condition, the state transitions are transparent to tasks other than fault recovery programs and, upon a fault condition, the faulted program.

Reconfigurable dual processor system

A dual processor system (100) with duplicated memory (114, 124) that has two modes (10, 11) of operation: a converged mode (10) in which one of the two processors (101, 102) is active and executing all tasks of the system while the other processor is inactive; and a diverged mode (11) in which both processors are active and executing substantially independently of each other different tasks of the system. The system automatically changes its modes of operation in response to requests such as manual and program control and certain system fault conditions. In the diverged mode, the system may be in either of two states of operation (1 and 2). In one state (1) one of the processors (101) is designated a primary processor, and in the other state (2) the other processor (102) is designated the primary processor. In the converged mode the system may be in either of four states of operation (3-6). In two of these states (3, 4) one of the processors is active while the other processor is standing by ready to take up execution of tasks from the point where the one processor stopped execution. In the other two of these states (5, 6) one of the processors is active while the other processor is out of service and cannot take up task execution without being initialized. The system (100) makes transitions between the various states in response to requests. Except for transitions of an active processor to an out-of-service condition, the state transitions are transparent to tasks other than fault recovery programs and, upon a fault condition, the faulted program.

Jonas Butvila

Papers

Reconfigurable dual processor system

Reconfigurable dual processor system and method for operating it