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

, 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 remembered ...

is laid out. The term "memory map" can have 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, a memory map is passed on from the

firmware In computing, firmware is a specific class of computer software that provides the low-level control for a device's specific hardware. Firmware, such as the BIOS of a personal computer, may contain basic functions of a device, and may provide ...

in order to instruct an

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

kernel Kernel may refer to: Computing * Kernel (operating system), the central component of most operating systems * Kernel (image processing), a matrix used for image convolution * Compute kernel, in GPGPU programming * Kernel method, in machine lea ...

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 very ...

implementations and

memory management unit A memory management unit (MMU), sometimes called paged memory management unit (PMMU), is a computer hardware unit having all memory references passed through itself, primarily performing the translation of virtual memory addresses to physical ...

s, a memory map refers to

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

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: * The ability to read or write multiple bits at a time, and * Using an a ...

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 or debugging tool is a computer program used to test and debug other programs (the "target" program). The main use of a debugger is to run the target program under controlled conditions that permit the programmer to track its execut ...

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 used at various levels by software and hardware. Memory addresses are fixed-length sequences of digits conventionally displayed and manipulated as unsigned integers. ...

es (such as

function pointer A function pointer, also called a subroutine pointer or procedure pointer, is a pointer that points to a function. As opposed to referencing a data value, a function pointer points to executable code within memory. Dereferencing the function point ...

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 firmware used to provide runtime services for operating systems and programs and to perform hardware initialization during the ...

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 tea ...

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