Double Data Rate SDRAM: Fast Performance at an Economical Price

ManualsBrandsHP ManualsServerHP ProLiant ML330 G2 Server

TECHNOLOGY BRIEF

Doc Number TC020603TB

June 2002

Compaq Computer

Corporation

Prepared by

ISS Technology

Communications

CONTENTS

Executive Summary......... 1

Notice ................................ 2

Introduction ...................... 3

SDRAM Operation ............ 3

How CAS Latency Affects

System Performance ..... 5

Double Data Rate

SDRAM .............................. 6

Differences between

Standard SDRAM and DDR

SDRAM.......................... 6

2n-Prefetch

Architecture ................ 6

Strobe-based Data

Bus ............................. 7

Signaling Technology. 7

Reduced Power

Requirements............. 8

DDR SDRAM DIMMs..... 8

DDR SDRAM

Performance .................. 8

The Future of DDR

SDRAM .............................. 9

Conclusion........................ 9

Double Data Rate SDRAM: Fast

Performance at an Economical Price

EXECUTIVE SUMMARY

Memory technology is continually evolving to keep pace with the bandwidth demands of

processors and server I/O interconnects. For some years synchronous DRAM has been the most

widely accepted memory technology due to its high performance (1 GB/s at 133 MHz). The

evolution from SDRAM to DDR SDRAM actually began in 1999, but its adoption was slowed by

what appeared to be more promising revolutionary memory technologies. DDR SDRAM is now

becoming more widely accepted in the server industry because of its faster performance (up to

2.7 GB/s at 166 MHz), power savings (2.5V compared to 3.3V for SDRAM), and lower cost than

competing memory technologies.

The JEDEC Solid State Technology Association (once known as the Joint Electron Device

Engineering Council) is now finalizing the specification for the next version of DDR SDRAM. The

new version, to be called DDR SDRAM II, will be backward compatible with DDR SDRAM and

will improve bus utilization to increase performance and bandwidth to yield a theoretical peak

bandwidth of 6.4 GB/s at 400 MHz.

Please direct comments regarding this communication to the ISS Technology Communications Group at this Internet

address: TechCom@hp.com

Summary of content (9 pages)

PAGE 1
TECHNOLOGY BRIEF .. .. .. .. .. .. Compaq Computer .. Corporation .. .. Prepared by .. .. ISS Technology .. Communications .. .. .. CONTENTS .. .. Executive Summary ......... 1 .. Notice ................................ 2 ... Introduction ...................... 3 ... SDRAM Operation ............ 3 ... .. How CAS Latency Affects . System Performance ..... 5 ... .. Double Data Rate . SDRAM .............................. 6 ... .. Differences between . Standard SDRAM and DDR ... SDRAM ..........................
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Double Data Rate SDRAM: Fast TECHNOLOGY BRIEF (cont.) .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . Doc Number TC020603TB 2 Performance at an Economical Price NOTICE Compaq shall not be liable for technical or editorial errors or omissions contained herein.
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Double Data Rate SDRAM: Fast TECHNOLOGY BRIEF (cont.) SDRAM: synchronous dynamic random access memory DDR: double data rate Doc Number TC020603TB .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .
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Double Data Rate SDRAM: Fast TECHNOLOGY BRIEF (cont.) .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . Doc Number TC020603TB 4 Performance at an Economical Price carries control signals that enable devices to negotiate for use of the memory bus.
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Double Data Rate SDRAM: Fast TECHNOLOGY BRIEF (cont.) Unbuffered DIMMs do not use any buffer logic chips. By eliminating propagation delay of the logic buffer during the first read/write operation, unbuffered DIMMs achieve slightly faster operation (by one clock cycle at the initial access). PC100: a DIMM that is rated at 8 ns and has other internal timing characteristics that allow it to function properly in a 100 MHz system. Doc Number TC020603TB .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .
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Double Data Rate SDRAM: Fast TECHNOLOGY BRIEF (cont.) .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .
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Double Data Rate SDRAM: Fast TECHNOLOGY BRIEF (cont.) .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . Doc Number TC020603TB 7 Performance at an Economical Price Strobe-based Data Bus In a synchronous system, data output and capture are referenced to transitions in the system clock.
PAGE 8
Double Data Rate SDRAM: Fast TECHNOLOGY BRIEF (cont.) .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . Doc Number TC020603TB 8 Performance at an Economical Price Reduced Power Requirements DDR SDRAM has another significant improvement. The voltage supply for DDR SDRAM uses only 2.5 V, instead of 3.3 V.
PAGE 9
Double Data Rate SDRAM: Fast TECHNOLOGY BRIEF (cont.) .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .