I am a bit new at this hardware stuff.

I read from Wikipedia that:

Memory bandwidth is the rate at which data can be read from or stored into a semiconductor memory by a processor.

So, what is ram speed, exactly? Because rams have a PC part which describes the bandwidth and DDR which describes the speed. What's the difference between these two?

  • Speed is Bus Clock of the memory (MHZ), Bandwidth is data transfer rate, measured in gigabytes per second. Bandwidth is a more accurate representation of performance. – Moab Jan 11 '16 at 22:42
  • @Moab What is Bus Clock? – Mark Read Jan 11 '16 at 22:59
  • @Ramhound Alright, I understand now. Thanks for answering – Mark Read Jan 11 '16 at 23:02
  • @Ramhound, yea, not so much. Technically "bandwidth" refers to the width of the frequency spectrum of a signal. Colloquially it is used to refer to throughput, otherwise known as "speed". – psusi Jan 12 '16 at 0:15
  • There is a quite good explanation at en.wikipedia.org/wiki/DDR_SDRAM – David Balažic Sep 17 '18 at 18:04

DDR is just an acronym for Double Data Rate.

Compared to single data rate (SDR) SDRAM, the DDR SDRAM interface makes higher transfer rates possible by more strict control of the timing of the electrical data and clock signals. Implementations often have to use schemes such as phase-locked loops and self-calibration to reach the required timing accuracy.

With data being transferred 64 bits at a time, DDR SDRAM gives a transfer rate of (memory bus clock rate) × 2 (for dual rate) × 64 (number of bits transferred) / 8 (number of bits/byte). Thus, with a bus frequency of 100 MHz, DDR SDRAM gives a maximum transfer rate of 1600 MB/s.

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