Memories of Things to Come

Too many RAM technologies on the market at once could confuse system upgraders.

Nebojsa Novakovic

Memory technology made a quantum leap in 1997 with nearly a dozen new DRAM and SRAM architectures. One of the new architectures, SDRAM, will be the prevailing standard in 1998 PC systems, but others will emerge toward the end of the year to rival it.

SDRAM

Synchronous DRAM provides burst rates of up to 150 MHz, significantly higher than the standard 60-ns, 40-MHz extended data out (EDO) DRAM in today's systems. SDRAMs with 64-Mb capacity are already shipping. Most of SDRAM's ini tial incompatibilities with Intel's strict timing specs for the i440LX (66-MHz bus) and i440BX (100-MHz bus) chip sets have been ironed out.

ESDRAM

Enhanced SDRAM is the latest in a string of enhanced memories developed by Ramtron, which focuses on chips with low latency and high sustained bandwidth.

DDR-SDRAM

To improve the per-pin bandwidth, you can transfer data on both edges of each clock. This technology is called double data rate (DDR). Most new memory architectures will use this capability. DDR-SDRAM, which is also known as SDRAM II, was finally approved as an official standard after vendor disagreements over data strobe and other design issues.

Direct RDRAM

Some six years ago, a small California start-up, Rambus, shocked the memory community with its Rambus DRAM . RDRAM offered 500-MHz memory bus throughput by using 8-bit buses with 250-MHz clocks and dual-data transfers using both clock edges, all with a pin count one-third of comparab le DRAM. You could even upgrade the memory in steps of one chip, offering unprecedented granularity. Rambus and Intel now have the specification for the next-generation Direct Rambus DRAM, which Intel hopes to use in its Willamette- and Merced-based systems in late 1999.

SLDRAM

Designed by the SyncLink consortium of major DRAM manufacturers, SLDRAM is a new royalty-free, open memory standard. In

some ways similar to Direct RDRAM, SLDRAM implements a command-driven, packet-oriented, 16-bit, 200-MHz dual-data bus with 400-MHz throughput (800-MBps bandwidth). Like Direct RDRAM, SLDRAM lowers memory-bus pin count by using a fast, narrow data path. Fewer signals means easier control of electromagnetic interference and skew, as well as simplified board routing.

CDRAM

Mitsubishi's cache DRAM, which is offered in 4-Mbit and 16-Mbit chips, uses a small amount of on-chip cache (16 Kb) together with a very wide 128-bit internal data bus to achieve both a very high burst rate of up to 10 0 MHz and a very short pipelined access time of 7 ns. Its SRAM and DRAM banks operate concurrently.

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Where to Find

Rambus

Mountain View, CA 
Phone:    415-903-3800
Internet: 
http://www.rambus.com



Ramtron

Colorado Springs, CO 
Phone:    800-545-3726
Phone:    719-481-7000
Internet: 
http://www.ramtron.com

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How Direct Rambus Gets 95% Efficiency

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Rambus and Ramtron in 1998

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AT A GLANC E: A mess of acronyms are fighting to be the RAM in your next system; SDRAM is the choice for 1998.

WHO SUPPORTS IT: Intel, Ramtron, Rambus, MoSys, SyncLink, Mitsubishi.