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Flat memory model or linear memory model refers to a memory addressing paradigm in which "memory appears to the program as a single contiguous address space." [ 1 ] The CPU can directly (and linearly ) address all of the available memory locations without having to resort to any sort of bank switching , memory segmentation or paging schemes.
The Multics operating system is probably the best known system implementing segmented memory. Multics segments are subdivisions of the computer's physical memory of up to 256 pages, each page being 1K 36-bit words in size, resulting in a maximum segment size of 1MiB (with 9-bit bytes, as used in Multics). A process could have up to 4046 segments.
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 equivalent structure in DOS is the Program Segment Prefix (PSP), a 256-byte (page-sized) structure, which is by default located exactly before offset 0 of the program's load segment, rather than in segment 0. A segment register is initialised to 0x10 less than the code segment, in order to address it. In 8-bit CP/M, it has the following ...
The memory model concept derives from the setup of the segment registers. For example, in the tiny model CS=DS=SS, that is the program's code, data, and stack are all contained within a single 64 KB segment. In the small memory model DS=SS, so both data and stack reside in the same segment; CS points to a different code segment of up to 64 KB.
One of the major improvements the PCI Local Bus had over other I/O architectures was its configuration mechanism. In addition to the normal memory-mapped and I/O port spaces, each device function on the bus has a configuration space, which is 256 bytes long, addressable by knowing the eight-bit PCI bus, five-bit device, and three-bit function numbers for the device (commonly referred to as the ...
In computing, protected mode, also called protected virtual address mode, [1] is an operational mode of x86-compatible central processing units (CPUs). It allows system software to use features such as segmentation, virtual memory, paging and safe multi-tasking designed to increase an operating system's control over application software.
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 notation. In real mode, in order to calculate the physical address of a byte of memory, the hardware ...