Memory controller

Source: Wikipedia, the free encyclopedia.

A memory controller, also known as memory chip controller (MCC) or a memory controller unit (MCU), is a digital circuit that manages the flow of data going to and from a computer's

main memory.[1][2] When a memory controller is integrated into another chip, such as being placed on the same die or as an integral part of a microprocessor
, it is usually called an integrated memory controller (IMC).

Memory controllers contain the logic necessary to read and write to

128-bit
memory device.

Some memory controllers, such as the one integrated into

virtual addressing
.

History

Older Intel and PowerPC-based computers have memory controller chips that are separate from the main processor. Often these are integrated into the northbridge of the computer, also sometimes called a memory controller hub.

Most modern desktop or workstation microprocessors use an integrated memory controller (IMC), including microprocessors from

ARM architecture
.

Prior to

AMD microprocessors had a memory controller implemented on their motherboard's northbridge. In K8 and later, AMD employed an integrated memory controller.[4] Likewise, until Nehalem (circa 2008), Intel microprocessors used memory controllers implemented on the motherboard's northbridge. Nehalem and later switched to an integrated memory controller.[5]

Other examples of microprocessor architectures that use integrated memory controllers include

NVIDIA's Fermi, IBM's POWER5, and Sun Microsystems's UltraSPARC T1
.

While an integrated memory controller has the potential to increase the system's performance, such as by reducing memory latency, 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.

Some microprocessors in the 1990s, such as the DEC

PA-7300LC
, had integrated memory controllers; however, rather than for performance gains, this was implemented to reduce the cost of systems by eliminating the need for an external memory controller.

Some CPUs are designed to have their memory controllers as dedicated external components that are not part of the chipset. An example is IBM

L4 cache chips, and as the actual memory controllers. The first version of the Centaur chip used DDR3 memory but an updated version was later released which can use DDR4.[6]

Security

A few experimental memory controllers (mostly aimed at the server market where data protection is legally required) contain a second level of address translation, in addition to the first level of address translation performed by the CPU's memory management unit.[7]

Memory controllers integrated into certain

pseudo-random patterns.[8][9]

Memory Scrambling (in Cryptographic Theory) is supposed to prevent

DRAM data remanence by effectively rendering various types of cold boot attacks
ineffective. In current practice this has not been achieved.

However Memory Scrambling has only been designed to address DRAM-related electrical problems. The late 2010s Memory Scrambling Standards do not fix or prevent security issues or problems. The 2010s Memory Scrambling standards are not cryptographically secure, or necessarily open sourced or open to public revision or analysis.[10]

ASUS and Intel have their own memory scrambling standards. Currently ASUS motherboards have allowed the user to choose which memory scrambling standards to use [ASUS or Intel] or whether to turn the feature off entirely.

Variants

Double data rate memory

Double data rate (DDR) memory controllers are used to drive DDR SDRAM, where data is transferred on both rising and falling edges of the system's memory clock. DDR memory controllers are significantly more complicated when compared to single data rate controllers [citation needed], but they allow for twice the data to be transferred without increasing the memory cell's clock rate or bus width.

Multichannel memory

Main article: Multi-channel memory architecture

Multichannel memory memory controllers are memory controllers where the DRAM devices are separated on to multiple different buses to allow the memory controller(s) to access them in parallel. This increases the theoretical amount of bandwidth of the bus by a factor of the number of channels. While a channel for every DRAM cell would be the ideal solution, adding more channels is very difficult due to wire count, line capacitance, and the need for parallel access lines to have identical lengths.

Fully buffered memory

Main article: Fully Buffered DIMM

Fully buffered memory systems place a memory buffer device on every

FB-DIMM
when Fully Buffered RAM is used), which unlike traditional memory controller devices, use a serial data link to the memory controller instead of the parallel link used in previous RAM designs. 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 on a single board), at the expense of increasing latency (the time necessary to access a memory location). This increase is due to the time required to 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 controller on the motherboard.

In theory, the FB-DIMM's memory buffer device could be built to access any DRAM cells, allowing for memory cell agnostic memory controller design, but this has not been demonstrated, as the technology is in its infancy.

Flash memory controller

Main article: Flash memory controller

Many

solid state drives, include a flash memory controller
. Flash memory is inherently slower to access than RAM and often becomes unusable after a few million write cycles, which generally makes it unsuitable for RAM applications.

See also

References

  1. ^ Comptia A+ Certification Exam Guide, Seventh Edition, by Mike Meyers, in the glossary, bottom of page 1278: "Chip that handles memory requests from the CPU."
  2. ISBN 9781590591307
    . Retrieved 6 February 2015.
  3. ^ "Memory Controller"
  4. ^ Vries, Hans de. "Chip Architect: AMD's Next Generation Micro Processor's Architecture". www.chip-architect.com. Retrieved 2018-03-17.
  5. ^ Torres, Gabriel (2008-08-26). "Inside Intel Nehalem Microarchitecture". Hardware Secrets. p. 2. Retrieved 7 September 2017.
  6. ^ Prickett Morgan, Timothy (2016-10-17). "IBM Brings DDR4 Memory To Bear On Power Systems". IT Jungle. p. 1. Retrieved 2017-09-07.
  7. ^ This is a security feature in that it allows the Operating System to provide better protection separate from using a bit to deny arbitrary code execution in (System and/or User) RAM memory areas. John Carter, Wilson Hsieh, Leigh Stoller, Mark Swansony, Lixin Zhang, et al. "Impulse: Building a Smarter Memory Controller".
  8. ^ "2nd Generation Intel Core Processor Family Desktop, Intel Pentium Processor Family Desktop, and Intel Celeron Processor Family Desktop" (PDF). June 2013. p. 23. Retrieved 2015-11-03.
  9. ^ "2nd Generation Intel Core Processor Family Mobile and Intel Celeron Processor Family Mobile" (PDF). September 2012. p. 24. Retrieved 2015-11-03.
  10. ^ Igor Skochinsky (2014-03-12). "Secret of Intel Management Engine". SlideShare. pp. 26–29. Retrieved 2014-07-13.

External links

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