Abstract: The export record of an operating system kernel employing dynamically-linked loading modules (e.g., portable-executable modules) is thunked so as to globally and forcibly redirect service requests from afterwards loaded modules to subclassing routines instead of to original servicing routines of the kernel. The base location of the kernel is determined from an Image.sub.-- Base entry of its disk-image. An offset storing position in the export record is overwritten with a value equal to the value of the address of the subclassing routine minus the kernel's base address. Use of the thunked export record is forced even for `bound` external references by altering the time stamp in the kernel's export record to a nonmatching value.

Abstract: A file defragmentation utility for a computer system is disclosed that enables multithreaded preemptive multi-tasking during file defragmentation. The utility includes a defragmentor routine that defragments clusters or portions of a file on a storage media and then updates one or more file system structures to indicate the new locations of the defragmented clusters of the file. An alias driver is provided that traps accesses to the file and that maintains coherent access to the file while the file system structures are updated.

Abstract: A method for allowing a protected mode kernel to service, in virtual 8086 mode, hardware interrupts which occur during execution of ring 0 protected mode code. When an interrupt occurs during execution of ring 0 code, the microprocessor copies the state of the last virtual 8086 environment on the top of the ring 0 stack and modifies this state to begin execution of the appropriate interrupt service routine in virtual 8086 mode. The kernel utilizes a secondary stack to keep track of the last virtual 8086 environment saved on the ring 0 stack and updates the ring 0 stack pointer in the respective task's task state segment to the new beginning of the ring 0 stack each time a ring transition occurs from ring 3 V86 mode to ring 0 protected mode. By manipulating the ring 0 stack and utilizing the secondary stack to keep track of interrupted V86 environments, the kernel can allow interrupts to be nested down multiple levels.