Dual-ported RAM (DPRAM), also called dual-port RAM, is a type of
random-access memory
Random-access memory (RAM; ) is a form of Computer memory, electronic computer memory that can be read and changed in any order, typically used to store working Data (computing), data and machine code. A random-access memory device allows ...
(RAM) that can be accessed via two different
buses
A bus (contracted from omnibus, with variants multibus, motorbus, autobus, etc.) is a motor vehicle that carries significantly more passengers than an average car or van, but fewer than the average rail transport. It is most commonly used ...
.
A simple dual-port RAM may allow only read access through one of the ports and write access through the other, in which case the same memory location cannot be accessed simultaneously through the ports since a write operation modifies the data and therefore needs to be synchronized with a read or another write operation.
A dual-port RAM may be built from single-port
memory cells to reduce cost or circuit complexity, and the performance penalty associated with it, which may still allow simultaneous read and write accesses to different memory locations depending on the partitioning of the memory array and having duplicate decoder paths to the partitions.
A true dual-port memory has two independent ports, which means that the memory array is built from dual-port memory-cells, and the address, data, and control lines of the two ports are connected to dedicated IO controllers so that the same memory location can be read through the ports simultaneously. A write operation through one of the ports still needs to be synchronized with a read or write operation to the same memory location through the other port.
Examples
Video RAM
Video random-access memory (VRAM) is dedicated computer memory used to store the pixels and other graphics data as a framebuffer to be rendered on a computer monitor. It often uses a different technology than other computer memory, in order to b ...
(VRAM) is a common form of dual-ported
dynamic RAM
Dynamics (from Greek δυναμικός ''dynamikos'' "powerful", from δύναμις ''dynamis'' " power") or dynamic may refer to:
Physics and engineering
* Dynamics (mechanics), the study of forces and their effect on motion
Brands and ente ...
mostly used for video memory, allowing the
central processing unit
A central processing unit (CPU), also called a central processor, main processor, or just processor, is the primary Processor (computing), processor in a given computer. Its electronic circuitry executes Instruction (computing), instructions ...
(CPU) to draw the image at the same time the video hardware is reading it out to the screen.
Apart from VRAM, most other types of dual-ported RAM are based on
static RAM
Static random-access memory (static RAM or SRAM) is a type of random-access memory (RAM) that uses latching circuitry (flip-flop) to store each bit. SRAM is volatile memory; data is lost when power is removed.
The ''static'' qualifier differ ...
technology.
Most CPUs implement the
processor register
A processor register is a quickly accessible location available to a computer's processor. Registers usually consist of a small amount of fast storage, although some registers have specific hardware functions, and may be read-only or write-onl ...
s as a small dual-ported or multi-ported RAM.
See also
*
Register file
A register file is an array of processor registers in a central processing unit (CPU). The instruction set architecture of a CPU will almost always define a set of registers which are used to stage data between memory and the functional units on ...
References
Computer memory
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