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In Windows 3.x, the WIN.COM starts KRNL286.EXE (standard mode) or KRNL386.EXE (386 enhanced mode). In Windows 9x, the WIN.COM starts VMM32.VXD . When all system configuration files and device drivers have been loaded, the 16-bit modules, KRNL386.EXE , GDI.EXE , and USER.EXE , are loaded, then the 32-bit DLLs ( KERNEL32.DLL , GDI32.DLL , and ...
Several computer systems introduced in the 1960s, such as the IBM System/360, DEC PDP-6/PDP-10, the GE-600/Honeywell 6000 series, and the Burroughs B5000 series and B6500 series, support two CPU modes; a mode that grants full privileges to code running in that mode, and a mode that prevents direct access to input/output devices and some other hardware facilities to code running in that mode.
A modern computer operating system usually uses virtual memory to provide separate address spaces or separate regions of a single address space, called user space and kernel space. [ 1 ] [ a ] Primarily, this separation serves to provide memory protection and hardware protection from malicious or errant software behaviour.
On Apple Mac computers using Intel x86-64 processor architecture, the EFI system partition is initially left blank and unused for booting into macOS. [13] [14]However, the EFI system partition is used as a staging area for firmware updates [15] and for the Microsoft Windows bootloader for Mac computers configured to boot into a Windows partition using Boot Camp.
In most existing systems, switching from user mode to kernel mode has an associated high cost in performance. It has been measured, on the basic request getpid, to cost 1000–1500 cycles on most machines. Of these just around 100 are for the actual switch (70 from user to kernel space, and 40 back), the rest is "kernel overhead".
The upper part is accessible only from kernel mode, and with some exceptions, is instantiated just once, system-wide. ntoskrnl.exe is mapped into this region, as are several other kernel mode components. This region also contains data used by kernel mode code, such as the kernel mode heaps and the file system cache.
During normal execution RAM is re-mapped to this location to improve performance, compared to the original ROM-based vector table. [ 10 ] The reset vector for MIPS32 processors is at virtual address 0xBFC00000, [ 11 ] which is located in the last 4 Mbytes of the KSEG1 non-cacheable region of memory. [ 12 ]
Before Windows 7, the system and boot partitions were, by default, the same and were given the "C:" drive letter. [7]: 971 Since Windows 7, however, Windows Setup creates, by default, a separate system partition that is not given an identifier and therefore is hidden. The boot partition is still given "C:" as its identifier.