Virtual Channel Memory

Emerging Technologies in Memory Architecture

With recent developments in PC multimedia applications, emphasis is shifting from size to speed when it comes to system memory. While many new technologies dedicated to increasing memory performance (DDRAM, ESDRAM, RAMBUS, DLDRAM, etc), this article will take a look at recent developments in NEC ' s " Virtual Channel Memory Architecture ".

This new architecture, realizes flexible and high-efficiency data transfer by incorporating channel buffers configured by high-speed registers. Virtual Channel Memory will be employed in large-capacity SDRAM and brought to market as a new standard that supports a wide range of applications, including multimedia PCs, workstations, and Internet servers.  This technology, while capable of outstanding data transfer speed, also maintains a very high compatibility with existing SDRAM architecture, allowing for easy system upgrades without the necessity of having to make many design changes.


The key feature of this new memory core technology, the "Virtual Channel Memory Architecture", is the incorporation of channel buffers configured by high-speed registers in the memory. Virtual Channel SDRAM performs read/write operations to and from these channel buffers from outside the memory's front-end processes. Alternatively, internal operations such as data transfer relays between memory cells and channel buffers, precharge and refresh of memory cells are performed separately from these front-end processes. As a result, background processing can be performed in parallel with foreground processing. By creating a support architecture for parallel processing, Virtual Channel SDRAM maintains a high average data transfer speed and exploits inherent memory performance to the highest possible extent.  NEC defines this new technology as a more "clever" approach to increasing the maximum transfer speed, and realizing truly high-speed characteristics.

VCM allows systems designers the freedom to design without being restricted by today’s confining memory operations because it allows the operation and management of the channels to be integrated into the chipset architecture.
In today's systems memory is accessed in a multitasking and sometimes conflicting manner by various memory masters. Each memory master has access to the memory with an address, a time locality, a block size and a number of contiguous accesses. Virtual Channel Memory can address this problem by providing an independent channel with its own resources to access the memory array. This results in lower overhead, low latency, high throughput and enhanced bus efficiency.



Features

High Data Transfer Efficiency
As internal operations such as precharge and refresh are performed in parallel with read and write operations from outside the memory, the data required for the next access can also be readied in advance. This parallel processing effectively lowers the wait time during random access that bottlenecks the average transfer speed of memory, supporting a higher data transfer efficiency.

Low Power Consumption
While front-end processing is performed (read/write to channel buffers), background processing, when not in use, can be set to idle, reducing the memory's power consumption.

High-Speed Access
The channel buffers used for performing read or write operations from outside the memory are configured by high-speed registers. Once data has been stored in a channel buffer, it can be accessed at extremely high speed. The channel buffers and memory cells are also connected via an extremely wide bus architecture that supports high-speed background processing.

Efficient Support for Multitasking
Channel buffers can be assigned to each memory master for multitasking manner executed by multiple memory masters. This enables considerable reduction of the waiting time of memory masters.

Upgrading of Existing SDRAMs Supported
Virtual Channel SDRAMs use the same pin configurations, packages, and interfaces as existing SDRAMs on the market, so that they can be used to upgrade existing SDRAMs as long as the memory controller within the chipset supports Virtual Channel SDRAM.

Comparison with Other Cached DRAMs
DRAM products that have a configuration similar to that of Virtual Channel SDRAM include ESDRAM and cached DRAM. Compared to these memory types, Virtual Channel SDRAM offers the most flexible control.

For more information on this exciting new technology, check out the Virtual Memory Resources page at NEC.

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