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Memory Bandwidth Clarification

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oopyseohs

Junior Member
HI. This is my first post @ anandtech

I have a question about memory bandwidth. I thought it was a relatively simple calculation at first, but then I came across a whole bunch of information on the topic that has made me very confused.

I understand that a Byte is 8 bits and its almost like my understanding has failed form that point forward.

Here is a typical example of my problem:
DDR400 = 200MHZ
200MHZ x 8-bits = 1600Mbps
1600Mbps x 2 (double data rate) = 3200Mbps

So that 3200Mbps is what? Peak bandwidth? Transfer Rate? Theoretical Bandwidth? Transfer Speed? WHAT IS THE DIFFERENCE?

To compound issues even further, almost at the bottom of this website there is a chart showing the peak bandwidth of various memory products. Under DDR400 it shows the Peak Bandwidth to be .8Gb/s (800Mbps). So how the hell was that calculated? Shouldnt it be 3200 like I though above? WHAT AM I MISSING?

So someone PLEASE PLEASE PLEASE help me out here. Give me a detailed and clear explanation of how the various numbers are calculated, PLEEEEEEEEEEASE.

Thankyou so much if ur able to help my noob-self out,

oopyseohs
😕
 
Actually it is a theoretical peak bandwidth of 3200 Mb/s. The number they put up is 0.8 GB/s - that means multiply it by 8 to get 3.2 Gb/s and by 1000 to get 3200 Mb/s like you said.

It looks like you forgot your understanding of bits/bytes or missed the memo about the abbreviations. 😛

EDIT: Oh yeah, and welcome to AT. 🙂
 
This figure is bandwidth as it occurs while data are actually transmitted. Addressing, latency, refresh, and other misc housekeeping take time as well, so that even in a perfect situation, you'll never see more than about 2750 MB/s from PC3200 RAM. (This value spotted on an AMD64 system where RAM access latency is as low as it possibly gets.)
 
HELLO NO TIME FOR INTRODUCTION BUT I AM THE BEST MATHAMATICAN IN THE WEST, THIS TOPIC HAS SOLVED THE HARDEST PROBLEM EVER AND I HAVE TO GO NOW.

THANK YOU FOR YOUR TIME AND I SHALL SEE YOU IN THE FUTURE.

PS PAYPAL ME MONEY TO FUND MY RESEARCH
 
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