The 386+ Memory Model

Written by: dimport Published by: Nightscript Published on: 2003-06-21 07:19:46 Topic: Hardware

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The 386+ processors have support for different kinds of memory models. It can address 2^(32) bytes(4 GB) of physical memory. It supports Flat Memory Model, Segementation memory model and real addressing mode memory model.

1.Flat Memory Model: In this model the whole 4 GB physical memory is considered as a single linear address space ranging from 0 to 2^(32). To acess a byte in the Flat memory model you just use the 32 bit pysical address.All the code,date, and the stack segments are in the same address spcae.Flat Memory model support paging. 2.Segmented Memory Model:In this model the memory appears as a group of independent address spaces each capable of addressing 2^(32) bytes fo memory. The 386+ processors support a total of 16,383 segments each of different sizes and types. The Segmented Memory Model can address a total of 2^(46)(64 Terabytes). The processor takes care of the address translation from logical address to physical address.To address a byte in Segment Memory model we need two parts a) A segment selector,which is a sixteen bit field that identifies a segment within the total 65,383 segment the processor can support. b)An offset,which is 32 bit ordinal that address the byte within the segment.It is 32 bits because the segment can address a max of 4 GB. Paging is supported in Segmented Memory model. A good explanation about how microprocessors work can be located by clicking here. This article was originally written by odonital

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