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The x86-64 architecture does not use segmentation in long mode (64-bit mode). Four of the segment registers, CS, SS, DS, and ES, are forced to base address 0, and the limit to 2 64. The segment registers FS and GS can still have a nonzero base address. This allows operating systems to use these segments for special purposes.
Four registers are used to refer to four segments on the 16-bit x86 segmented memory architecture. DS (data segment), CS (code segment), SS (stack segment), and ES (extra segment). Another 16-bit register can act as an offset into a given segment, and so a logical address on this platform is written segment:offset, typically in hexadecimal ...
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) contains the following ...
In a system using segmentation, computer memory addresses consist of a segment id and an offset within the segment. [3] A hardware memory management unit (MMU) is responsible for translating the segment and offset into a physical address, and for performing checks to make sure the translation can be done and that the reference to that segment and offset is permitted.
The CPU in modern computer hardware performs reads and writes to memory most efficiently when the data is naturally aligned, which generally means that the data's memory address is a multiple of the data size. For instance, in a 32-bit architecture, the data may be aligned if the data is stored in four consecutive bytes and the first byte lies ...
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.
Early x86 processors use the segmented memory model addresses based on a combination of two numbers: a memory segment, and an offset within that segment. Some segments are implicitly treated as code segments, dedicated for instructions, stack segments, or normal data segments.
Load segment limit from the specified segment descriptor. Sets ZF=1 if the descriptor could be loaded, ZF=0 otherwise. [j] VERR r/m16: 0F 00 /4: Verify a segment for reading. Sets ZF=1 if segment can be read, ZF=0 otherwise. VERW r/m16: 0F 00 /5: Verify a segment for writing. Sets ZF=1 if segment can be written, ZF=0 otherwise. [k] LOADALL [l ...