Abstract: A computer system is interrupted, and its entire state information is extracted as one or more checkpoints at one or more respective points during operation of the system. The checkpoint may be restored into the system at any later time, even multiple times, and it may also even be loaded into one or more other systems; all systems loaded with the same checkpoint will then execute from the same checkpointed state. The state extraction mechanism is preferably a virtual machine monitor, on which one or more virtual machines are installed, each virtual machine constituting an encapsulated, virtualized computer system whose states can be checkpointed under control of the virtual machine monitor. Checkpoints may be stored on a portable memory device or transmitted as a batch or dynamically over a network so that even virtual machines installed at different sites may execute from the same state.

Abstract: One or more virtual machines (VM's) run via a virtual machine monitor (VMM) on a hardware platform that has a segmented memory architecture. Each VM has at least one VM descriptor table that has, as entries, VM segment descriptors. At least one VMM descriptor table is established, including at least one shadow descriptor table that stores shadow descriptors for certain of the VM segment descriptors, which are then shadowed descriptors. The VMM compares the shadow descriptors with their respective corresponding shadowed VM descriptors, detects any lack of correspondence between the shadow descriptor table and the corresponding VM descriptor table, and updates and thereby synchronizes each shadow descriptor with its respective shadowed VM descriptor no later than, and preferably only upon the first use of, the respective descriptor by the VM.

Abstract: A dynamic binary translator converts input instruction sequences into output instruction sequences that are stored in a translation cache. In order to maintain coherence of the translation cache with the run-time version of the input instructions, translated code is checked by either a conflict detection mechanism or a code-invariance mechanism. For conflict detection, the system preferably uses memory traces generated by the memory management unit of the underlying hardware processor. In order to check for code-invariance, preludes for comparing cached, output instruction sequences with their supposed run-time input instruction equivalents are appended to the cached instructions themselves. Changes in the input sequences then result only in retranslation of instruction sequences in which at least one instruction has changed; this avoids costly total flushes of the translation cache.

Abstract: A virtual machine monitor (VMM) is included in a computer system that has a protected host operating system (HOS). A virtual machine running at least one application via a virtual operating system is connected to the VMM. Both the HOS and the VMM have separate operating contexts and disjoint address spaces, but are both co-resident at system level. A driver that is downloadable into the HOS at system level forms a total context switch between the VMM and HOS contexts. A user-level emulator accepts commands from the VMM via the system-level driver and processes these commands as remote procedure calls. The emulator is able to issue host operating system calls and thereby access the physical system devices via the host operating system. The host operating system itself thus handles execution of certain VMM instructions, such as accessing physical devices.

Abstract: In a computer that has hardware processor, and a memory, the invention provides a virtual machine monitor (VMM) and a virtual machine (VM) that has at least one virtual processor and is operatively connected to the VMM for running a sequence of VM instructions, which are either directly executable or non-directly executable. The VMM includes both a binary translation sub-system and a direct execution sub-system, as well as a sub-system that determines if VM instructions must be executed using binary translation, or if they can be executed using direct execution. Shadow descriptor tables in the VMM, corresponding to VM descriptor tables, segment tracking and memory tracing are used as factors in the decision of which execution mode to activate. The invention is particularly well-adapted for virtualizing computers in which the hardware processor has an Intel x86 architecture.

Abstract: The problem of extending modern operating systems to run efficiently on large-scale shared memory multiprocessors without a large implementation effort is solved by a unique type of virtual machine monitor. Virtual machines are used to run multiple commodity operating systems on a scalable multiprocessor. To reduce the memory overheads associated with running multiple operating systems, virtual machines transparently share major data structures such as the operating system code and the file system buffer cache. We use the distributed system support of modem operating systems to export a partial single system image to the users. Two techniques, copy-on-write disks and the use of a special network device, enable transparent resource sharing without requiring the cooperation of the operating systems. This solution addresses many of the challenges facing the system software for these machines.