I'm confused..


I’m fairly new to computers and I‘m trying to understand some things. I’m very confused. I’m hoping someone can help me out with my query. Can someone explain the whole concept of CPU FSB, L1 cache, and L2 cache, motherboard BUS Speed and how all those interact to effect computer performance?
Let me explain my system and then I’ll show my ignorance by asking specific questions.
My system:
I have a board that allows me to set the CPU/FSB Frequency (whatever that is) at 133MHz or 100MHz. It is presently set at 133MHz. My CPU is a 1335Mhz Athlon XP 1500 with 266Mhz FSB (?) and it has a L1 cache (?) of 64K and 256KB of L2 cache (?). According to my manuals my VIA KL133a chipset has a 200/266 Mhz FSB. I have 512MB of 133MHz SDRAM (my board does not support DDR RAM, whatever that is).

Questions: Is the 133MHz the BUS speed of the whole motherboard? If so, does it mean that although my CPU has a FSB (I’m assuming FSB is a similar type of BUS specifically for the CPU??) of 266MHz that it can only use 133MHz of that 266Mhz to communicate with the motherboard and components on the motherboard such as my chipset? Basically I’m led to believe that all communication between all components on the motherboard is done at 133MHz, as it’s the speed of the motherboard BUS. Yes/No? If this is the case why are all the components produced with varying speeds when their actual operating speed will be determined by the motherboard BUS speed? If this is not the case please enlighten me!!

What is L1 and L2 cache and what does it do? I know it is some sort of high speed memory for the CPU but why is there two types?
Also my memory is PC133 SDRAM. Recommended RAM for my CPU is DDR RAM but my board does not support it. How does this affect my system?

I have been on the net trying to find all this out and although I can get individual explanations I have found nothing that explains how all this interacts, assuming of course it does interact? I know I’m asking a lot but I appreciate any help given or links to information that may help.
Regards Dave, Ireland
4 answers Last reply
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  1. Wow! Almost nothing to explain ;-)

    A CPU works at a given velocity, in your case 1333 Mhz. This is the result of 10 (multiplier) times 133 (frecuency).

    Another thing is the velocity of the memory. In your case is 133Mhz. But DDRRAM is able to transmit information in the raising and falling of each cycle. For this reason is called "266Mhz", because in theory is doubled. It is possible to run your CPU with SDRAM and DDRAM, but usually a mobo is designed for just one (hey, there is some exceptions that con use both).

    As you pointed out, your XP comunicates with the chipset (it's like a center of comunications, distributes everything and pass the demands between components) at 266Mhz, but the chipset comunicates with the SDRAM at 133Mhz. Is this bad? Well, what happens is that probably your CPU is usually "waiting" for the information coming from the RAM. So, in fact if you were using a DDR mobo the overall performance would be increased largely.

    Finally, the L1 and L2 cache. This memory is located inside the CPU. Thing of it as a superfast memory that holds repeated actions, important adresses, stores data if the CPU is working in other things, etc. Don't ask me exactly what they do, but the trend is to increase L2 memory, because you gain some performance (it depends of the CPU and configuration).

    More questions?

    DIY: read, buy, test, learn, reward yourself!
  2. Hello,

    Beware of fancy dancers.
    Don't make any adjustments based on learned advice just yet, or next you'll be wondering why you can only get a black screen.
    You left out the most important piece of information. What motherboard are you using?
    Post again, and we'll go from there.

    Regards to all.
  3. Thanks baldurga and Telaman.
    My Mobo is an ASUS A7VC. It’s part of an ASUS Terminator bare bone system (as I said I’m new to computers so for a first machine I didn’t splash out). It’s a basic enough mobo with 2 SDRAM DIMM sockets (as I said it only supports PC100 and PC133 SDRAM DIMMS), 2 PCI and 1 AMR expansion slot (NO VGA expansion slot), on-board S3 graphics (via the chipset Northbridge) and on-board AC ’97 audio (via the Southbridge). I guess if I could use DDR RAM I would.
    So what then does the BUS speed of the mobo itself signify? Is the 133MHz actually the BUS speed of the mobo? If so is there not some sort of conflict between the 133Mhz speed of the mobo and the 266MHz speed of the CPU? Is it simply a case of the CPU being too quick for the mobo??!!
    Cheers folks…. It’s great to get this finally understood. Keep the replies coming!!
  4. DDR stands for Double Data Rate, basicly getting twice the data over the same bus speed. So, 133 DDR is 266. The athlon runs on a 133 DDR Bus (or 266). With 133 memory, it only can access the memory at 133, so the who bus isn't sued.

    L1 Cache and L2 Cache are CPU architecture functions that speed up the CPU by allowing the CPU to bypass accessing your main memory for faster memory built onto the CPU. They are used in various ways (I'm not sure exactly how, but it's not that big of a deal) that can differ from chip to chip (P4 to Athlon XP, not from XP to XP). The L1 and L2 store different pieces of data, at different CPU stages of the computing process.

    Unfortunately, a motherboard BUS is quite complex, with several different parts of it running at different speeds. In general, the FSB is considered what your memory and/or your CPU runs at. In your case, they are both 133. Even though your CPU uses a DDR interface to get a throughput of 266, it is still running at 133 (Actualy, the CPU is running at 10 times the speed of the bus to achive a CPU clock of 1.333 Ghz). The PCI bus, where your sound cards, network cards, and other expansion cards work, runs at 33, and your AGP slot that runs for your video card runs at 66.

    Hope this helps.

    "Search your feelings you know it to be true, I am your... twin sister" - Darth Vader
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