Bus and cache speeds for dummies

Discussion in 'General Mac Discussion' started by reemas, Jan 13, 2004.

  1. reemas macrumors member

    Joined:
    Jan 6, 2004
    #1
    Can someone please help:
    I posted before asking the diff between notebooks and desktops with the same specifications. For the most part I now know that unless the specs are truly identical, desktops are faster.

    But someone said usually 1 GHz notebook doesn't have the same cache and bus speeds as a 1GHz desktop.

    I looked this up on Apple's site and noticed the following:

    Current model powerbooks (15-inch):
    1GHz or 1.25GHz PowerPC G4 processor with Velocity Engine
    512K SRAM on-chip L2 cache
    167MHz system bus

    Previous generation G4 PowerMacs:
    1.25GHz PowerPC G4 processor
    Full 128-bit internal memory data paths
    256K on-chip L2 cache running at processor speed
    1MB DDR SRAM L3 cache per processor (2MB DDR SRAM L3 cache per processor with dual 1.25GHz PowerPC G4 build-to-order option)
    167MHz system bus supporting over 1.3GBps data throughput

    Could someone please explain L2 vs L3 cache and what it means and does to me?
    Also, where does bus speed come in and how does it affect things?
    I'm guessing the desktop is faster?

    Thanks for your time.
     
  2. G5orbust macrumors 65816

    G5orbust

    Joined:
    Jun 14, 2002
    #2
    Re: Bus and cache speeds for dummies

    Can someone please help:
    I posted before asking the diff between notebooks and desktops with the same specifications. For the most part I now know that unless the specs are truly identical, desktops are faster.

    But someone said usually 1 GHz notebook doesn't have the same cache and bus speeds as a 1GHz desktop.

    I looked this up on Apple's site and noticed the following:


    Theyre wrong. The laptop FSB speeds are the same as the desktop versions of the G4.


    Could someone please explain L2 vs L3 cache and what it means and does to me?
    Also, where does bus speed come in and how does it affect things?
    I'm guessing the desktop is faster?


    L2 cache holds data in super fast memory that feeds directly into the CPU. This memory runs at processor speed. L3 cache is larger and its used for more application data that is pumped into the CPU at faster than FSB speeds but it is fractional to proc speed. A higher amount of L2 cache will yield more performance than a proportional amount of L3 cache.

    Bus speed directly effects processor clock via the multiplyer. The bus speed in actuality represents how much data can be pushed through in one cycle. If I were to compare since 1.25GHz G4s in the given laptop and desktop models, the laptop would be faster due to its larger amount of L2 cache.
     

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