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Re: [linux-dell-laptops] CL2-memory for 4100

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  • jsc3@havoc.gtf.org
    ... Actually, I have seen it claimed by folks I trust that PC100 CL2 is actually faster in the scheme of things than PC133 CL3. ... This is the key point - I
    Message 1 of 3 , Nov 29, 2001
      > I don't think that it would make a noticable differance. The 512 leaves you
      > with a better upgrade path, which (in my opinion) is better than CL2.
      > I don't think that the memory controler (being CL2 or CL3) will make too
      > much difference because the speed bottle necks are elsewhere is the system.

      Actually, I have seen it claimed by folks I trust that PC100 CL2 is actually
      faster in the scheme of things than PC133 CL3.

      > >is it adressed as CL3 anyway?

      This is the key point - I believe that on the Inspiron 4000 and 8X00
      at least, the memory timing is going to be 3-2-2 (CL3) no matter what
      kind of memory you install. Certainly the BIOS (I am currently
      using A17, which I think is the most recent for I8X00) does not seem
      to provide any way to tweak memory timings, unlike the BIOS of every
      desktop system I currently own.

      > CL is a measure of latency, not bandwidth so the system memory addressing
      > system would not it change much.

      Ah, but latency does affect overall system throughput, particularly when
      the memory latencies are much larger than the clock cycle (which they
      are - think about, PC133 memory, and then waiting two memory or three
      memory clock cycles over that, when used with a 1.2 GHz CPU, which has
      a clock 9 times faster than the memory clock).

      This is one reason that Rambus RAM (RDRAM) has not provided the performance
      improvement that everybody expected. Theoretically, PC800 RDRAM has a
      maximum memory bandwidth of 3.2 gigabytes per second, while PC2100 DDR
      has a maximum memory bandwidth of 2.1 gigabytes per second, and PC133
      SDRAM has a maximum bandwidth of about 1 gigabyte per second.

      However, the latency of Rambus RDRAM is much higher than SDR or DDR
      SDRAM and thus for many applications even plain old PC133 memory provides
      higher throughput than RDRAM, and for almost all real-world applications
      DDR seems to produce a higher throughput than RDRAM, even though RDRAM
      has a 50% higher maximum bandwidth - the difference is almost entirely
      due to the lower latency of DDR SDRAM.

      > I have ordered 512MB CL3, Doubling to RAM capacity is more important to me.

      This is probably the best choice.

      > It is personal Preference really, - I am no expert.

      I believe in this case, you will lose nothing by your decision, since Dell
      indicates that the Dell laptops run at CL3 memory timings and I have not
      seen any evidence that would lead me to believe otherwise. If I did think
      that there was some way to get CL2 timing, I would advise buying CL2 memory
      as that would provide a 5-10% improvement in memory/CPU throughput (it
      would be higher, but the L1 and L2 cache must also be considered, and
      their latencies are much lower than the system RAM).

      > -----Original Message-----
      > From: Peer Soehring [mailto:Peer_Soehring@...-hamburg.de]
      > Sent: Wednesday, 28 November 2001 12:00 AM
      > To: linux-dell-laptops@yahoogroups.com
      > Subject: [linux-dell-laptops] CL2-memory for 4100
      > Hello,
      > I checked crucial and noticed they sell 128 and 256 MB CL2, but 512 MB CL3 -
      > should I get CL2 memory for the 4100 or is it adressed as CL3 anyway?
      > Peer Soehring

      John Cronin
      mailto: `echo NjsOc3@... | sed 's/[NOSPAM]//g'`
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