Memory Controller

The memory controller is a digital circuit which manages the flow of data going to and from the main memory. It can be a separate chip or integrated into another chip, such as on the die of a microprocessor. This is also called a Memory Chip Controller (MCC).

Computers using Intel microprocessors have traditionally had a memory controller implemented on their motherboard's northbridge, but many modern microprocessors, such as DEC/Compaq's Alpha 21364, AMD's Athlon 64 and Opteron processors, IBM's POWER5, Sun Microsystems's UltraSPARC T1, and more recently Intel's Core i7 have an integrated memory controller (IMC) on the microprocessor in order to reduce memory latency. While this has the potential to increase the system's performance, it locks the microprocessor to a specific type (or types) of memory, forcing a redesign in order to support newer memory technologies. When DDR2 SDRAM was introduced, AMD released new Athlon 64 CPUs. These new models, with a DDR2 controller, use a different physical socket (known as Socket AM2), so that they will only fit in motherboards designed for the new type of RAM. When the memory controller is not on-die, the same CPU may be installed on a new motherboard, with an updated northbridge.

The integration of the memory controller onto the die of the microprocessor is not a new concept. Some microprocessors in the 1990s such as the DEC Alpha 21066 and HP PA-7300LC had integrated memory controllers, but rather than for performance gains, this was implemented to reduce the cost of systems by eliminating the need for an external memory controller.

Read more about Memory Controller:  Purpose, Double Data Rate Memory, Dual-channel Memory, Fully Buffered Memory

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... In addition to the Phenom II's pin compatibility, the AM3 memory controller supports both DDR2 and DDR3 memory (up to DDR2-1066 and DDR3-1333), allowing existing AM2+ users to upgrade their CPU without changing ... The dual-spec memory controller also gives motherboard manufacturers and system builders the option of pairing AM3 with DDR2, as compared to competing chips from Intel which ...
Alpha 21364 - Description - Memory Controller
... The Alpha 21364 has two integrated memory controllers that support Rambus DRAM (RDRAM) that operate at two thirds of the microprocessor's clock frequency, or 800 MHz at 1.2 GHz ... Compaq designed custom memory controllers for the Alpha 21364, giving them capabilities not found in standard RDRAM memory controllers such as having all the 128 pages ... Each memory controller provides five RDRAM channels that support PC800 Rambus inline memory modules (RIMMs) ...
Memory Refresh - How DRAM Refresh Works - Types of Refresh Circuits
... hibernation without stopping the refresh process and losing the data in memory ... refresh is handled by circuits in the memory controller, or increasingly on the chip itself ... This counter may be part of the memory controller circuitry, or on the memory chip itself ...
Memory Controller - Fully Buffered Memory
... Fully buffered memory systems place a memory buffer device on every memory module (called an FB-DIMM when Fully Buffered RAM is used), which unlike traditional memory controller devices, use a serial data link to the ... This decreases the number of the wires necessary to place the memory devices on a motherboard (allowing for a smaller number of layers to be used, meaning more memory devices can be placed ... convert the parallel information read from the DRAM cell to the serial format used by the FB-DIMM controller, and back to a parallel form in the memory ...
Ultra SPARC III - Memory Controller
... The UltraSPARC has an integrated memory controller and implements a dedicated 128-bit bus operating at 150 MHz to access up to 4 GB of "local" memory ... The integrated memory controller is used to reduce latency and thus improve performance, unlike some other UltraSPARC microprocessors that use the feature to reduce cost ...

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