Aperture (computer memory)
Encyclopedia
In computing
, an aperture is a portion of the address space
which is persistently associated with a particular peripheral device or a memory
unit. Apertures may reach external devices such as ROM
or RAM chips, or internal memory on the CPU
itself.
Typically a memory device attached to a computer accepts addresses starting at zero, and so a system with more than one such device would have ambiguous addressing. To resolve this, the memory logic will contain several aperture selectors, each containing a range selector and an interface to one of the memory devices. The set of selector address ranges of the apertures are disjoint. When the CPU presents a physical address within the range recognized by an aperture, the aperture unit routes the request (with the address remapped to a zero base) to the attached device. Thus apertures form a layer of address translation below the level of the usual virtual-to-physical mapping.
Computing
Computing is usually defined as the activity of using and improving computer hardware and software. It is the computer-specific part of information technology...
, an aperture is a portion of the address space
Address space
In computing, an address space defines a range of discrete addresses, each of which may correspond to a network host, peripheral device, disk sector, a memory cell or other logical or physical entity.- Overview :...
which is persistently associated with a particular peripheral device or a memory
Computer memory
In computing, memory refers to the physical devices used to store programs or data on a temporary or permanent basis for use in a computer or other digital electronic device. The term primary memory is used for the information in physical systems which are fast In computing, memory refers to the...
unit. Apertures may reach external devices such as ROM
Read-only memory
Read-only memory is a class of storage medium used in computers and other electronic devices. Data stored in ROM cannot be modified, or can be modified only slowly or with difficulty, so it is mainly used to distribute firmware .In its strictest sense, ROM refers only...
or RAM chips, or internal memory on the CPU
Central processing unit
The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...
itself.
Typically a memory device attached to a computer accepts addresses starting at zero, and so a system with more than one such device would have ambiguous addressing. To resolve this, the memory logic will contain several aperture selectors, each containing a range selector and an interface to one of the memory devices. The set of selector address ranges of the apertures are disjoint. When the CPU presents a physical address within the range recognized by an aperture, the aperture unit routes the request (with the address remapped to a zero base) to the attached device. Thus apertures form a layer of address translation below the level of the usual virtual-to-physical mapping.