computer science Computer science is the study of computation, information, and automation. Computer science spans Theoretical computer science, theoretical disciplines (such as algorithms, theory of computation, and information theory) to Applied science, ...

, a memory map is a structure of data (which usually resides in memory itself) that indicates how

memory Memory is the faculty of the mind by which data or information is encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If past events could not be remembe ...

is laid out. The term "memory map" has different meanings in different contexts. #It is the fastest and most flexible cache organization that uses an associative memory. The associative memory stores both the address and content of the memory word. #In the boot process of some computers, a memory map may be passed on from the

firmware In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computer, computing machinery. It includes the study and experimentation of algorithmic processes, and the development of both computer hardware, h ...

to instruct an

operating system An operating system (OS) is system software that manages computer hardware and software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ...

kernel about memory layout. It contains the information regarding the size of total memory, any reserved regions and may also provide other details specific to the architecture. #In

virtual memory In computing, virtual memory, or virtual storage, is a memory management technique that provides an "idealized abstraction of the storage resources that are actually available on a given machine" which "creates the illusion to users of a ver ...

implementations and

memory management unit A memory management unit (MMU), sometimes called paged memory management unit (PMMU), is a computer hardware unit that examines all references to computer memory, memory, and translates the memory addresses being referenced, known as virtual mem ...

s, a memory map refers to

page table A page table is a data structure used by a virtual memory system in a computer to store mappings between virtual addresses and physical addresses. Virtual addresses are used by the program executed by the accessing process, while physical addr ...

s or

hardware register In digital electronics, especially computing, hardware registers are circuits typically composed of flip-flops, often with many characteristics similar to memory, such as: * Using an memory or port address to select a particular register in a ma ...

s, which store the mapping between a certain process's virtual memory layout and how that space relates to physical memory addresses. #In native

debugger A debugger is a computer program used to test and debug other programs (the "target" programs). Common features of debuggers include the ability to run or halt the target program using breakpoints, step through code line by line, and display ...

programs, a memory map refers to the mapping between loaded executable(or)library files and memory regions. These memory maps are used to resolve

memory address In computing, a memory address is a reference to a specific memory location in memory used by both software and hardware. These addresses are fixed-length sequences of digits, typically displayed and handled as unsigned integers. This numeric ...

es (such as

function pointer A function pointer, also called a subroutine pointer or procedure pointer, is a pointer referencing executable code, rather than data. Dereferencing the function pointer yields the referenced function, which can be invoked and passed arguments ...

s) to actual symbols.

PC BIOS memory map

BIOS In computing, BIOS (, ; Basic Input/Output System, also known as the System BIOS, ROM BIOS, BIOS ROM or PC BIOS) is a type of firmware used to provide runtime services for operating systems and programs and to perform hardware initialization d ...

for the

IBM Personal Computer The IBM Personal Computer (model 5150, commonly known as the IBM PC) is the first microcomputer released in the IBM PC model line and the basis for the IBM PC compatible ''de facto'' standard. Released on August 12, 1981, it was created by a ...

and compatibles provides a set of routines that can be used by operating system or applications to get the memory layout. Some of the available routines are: BIOS Function: INT 0x15, AX=0xE801: This BIOS interrupt call is used to get the memory size for 64MB+ configurations. It is supported by AMI BIOSses dated August 23, 1994 or later. The caller sets AX to 0xE801 then executes int 0x15. If some error has happened, the routine returns with CF (Carry Flag) set to 1. If no error, the routine returns with CF clear and the state of registers is described as following: BIOS Function: INT 0x15, AX=0xE820 - GET SYSTEM MEMORY MAP: Input: SMAP buffer structure: How used: The operating system shall allocate an SMAP buffer in memory (20 bytes buffer). Then set registers as specified in "Input" table. On first call, EBX should be set to 0. Next step is to call INT 0x15. If no error, the interrupt call returns with CF clear and the buffer filled with data representing first region of the memory map. EBX is updated by BIOS so that when the OS calls the routine again, The next region is returned in the buffer. BIOS sets EBX to zero if all done.

References

Computer memory {{compsci-stub

PC BIOS memory map

See also

References