lkml.org 
[lkml]   [2000]   [Aug]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: DRAM to CPU Frequency Ratio (Athlon)
    Ookhoi wrote:
    >
    > Hi Marc,
    >
    > > > I have two exactly the same Athlon systems at 750MHz and 512 meg memory
    > > > (@ 133MHz). In the BIOS there is a option: "DRAM to CPU Frequency
    > > > Ratio", which can be 3:3 or 4:3. The Help says: "Using this item to set
    > > > the operating frequency of DRAM".
    > > >
    > > > I just installed Debian on the machines, rebooted, changed one machine
    > > > to 3:3, the other was 4:3, and compiled a kernel on both of them. The
    > > > time it took was almost exactly the same (about 5 min 32 sec). The 3:3
    > > > one was 0.24 seconds faster.
    > > >
    > > > Does Linux ignore the DRAM to CPU Frequency Ratio (if at all possible),
    > > > is it just a useless BIOS option (because of hardware limits or
    > > > something), or is it not supposed to make the machine faster (if, what
    > > > _does_ it do then ;-) ? (the book that came with the machine doesn't
    > > > tell me much about the option).
    > > >
    > > <snip>
    > >
    > > You have PC133-333 RAM installed (PC133-222 SDRAM is still hard to find)
    > > which may also be run as PC100-222. So, when you select a ratio of 3:3,
    > > then the RAM runs in PC100-222 mode, which is not too much slower than
    > > PC133-333:
    > >
    > > 2*1/100e6 = 1/50e6 is actually smaller than 3*1/133e6 = 1/44e6.
    > >
    > > There are _many_ factors to SDRAM timing, but the bottomline is that you
    > > will only see a difference (of then ca. 5%, which sounds tiny, but is
    > > approximately the same gain as when going from a 600 to a 650 MHz CPU)
    > > if you use PC133-222 SDRAM.
    >
    > Thank you for your reaction. Others on the list also said that with a
    > kernel compile, disk speed is a bottleneck, not memory.
    >
    > What is the difference between PC133-333 and PC133-222, and is that also
    > the difference between RAM and SDRAM? Do you have an url to more info
    > about this (and other factors to SDRAM timing)? TIA!
    >

    The full spec:
    http://developer.intel.com/technology/memory/pcsdram/spec/index.html

    The most important parameters (from approx. 30?)

    PARAMETER SYMBOL
    cycle period t_CK
    CAS Latency CL
    RAS-to-CAS Delay t_RCD
    RAS Precharge Time t_RP
    Output Valid from Clock t_AC
    RAS Cycle Time t_RC
    RAS Active Time t_RAS

    The PC-blah-blah convention is also spec'ed in the above document, but
    here comes the short story:

    PC<1/t_CK>-<CL><t_RCD><t_RP>

    where 1/t_CK is in MHz, CL, t_RCD and t_RP are in units of t_CK.

    If you speak German, you can read all that in c't, issue 17/00, pp.166.

    Marc

    --
    Marc Mutz <Marc@Mutz.com> http://marc.mutz.com/Encryption-HOWTO/
    University of Bielefeld, Dep. of Mathematics / Dep. of Physics

    PGP-keyID's: 0xd46ce9ab (RSA), 0x7ae55b9e (DSS/DH)

    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2005-03-22 12:38    [W:0.030 / U:0.632 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site