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x86 memory segmentation. The Intel x86 computer instruction set architecture has supported memory segmentation since the original Intel 8086 in 1978. It allows programs to address more than 64 KB (65,536 bytes) of memory, the limit in earlier 80xx processors. In 1982, the Intel 80286 added support for virtual memory and memory protection; the ...
Segment descriptor. In memory addressing for Intel x86 computer architectures, segment descriptors are a part of the segmentation unit, used for translating a logical address to a linear address. Segment descriptors describe the memory segment referred to in the logical address. [1] The segment descriptor (8 bytes long in 80286 and later ...
Global Descriptor Table. The Global Descriptor Table (GDT) is a data structure used by Intel x86 -family processors starting with the 80286 in order to define the characteristics of the various memory areas used during program execution, including the base address, the size, and access privileges like executability and writability.
if X = 1 then the segment is a code segment; if X = 0 then the segment is a data segment. S is the Segment type bit, which should generally be cleared for system segments; [38] DPL is the Descriptor Privilege Level; P is the Present bit; D is the Default operand size; G is the Granularity bit; Bit 52 of the 80386 descriptor is not used by the ...
The default OperandSize and AddressSize to use for each instruction is given by the D bit of the segment descriptor of the current code segment - D=0 makes both 16-bit, D=1 makes both 32-bit. Additionally, they can be overridden on a per-instruction basis with two new instruction prefixes that were introduced in the 80386:
Memory segmentation is an operating system memory management technique of dividing a computer 's primary memory into segments or sections. In a computer system using segmentation, a reference to a memory location includes a value that identifies a segment and an offset (memory location) within that segment. Segments or sections are also used in ...
Task state segment. The task state segment (TSS) is a structure on x86 -based computers which holds information about a task. It is used by the operating system kernel for task management. Specifically, the following information is stored in the TSS: Processor register state. I/O port permissions.
A memory-mapped file is a segment of virtual memory [1] that has been assigned a direct byte-for-byte correlation with some portion of a file or file-like resource. This resource is typically a file that is physically present on disk, but can also be a device, shared memory object, or other resource that an operating system can reference through a file descriptor.