So what else could be holding our CPU back? What could be affecting the scalability of the Pentium 4 platform?
Back to our office intern. Suppose he is so good at collating that he can collate documents faster than the boss can hand them to him. Now we have a completely different ballgame. Instead of a slow intern holding up the company, itís actually the bossí inability to feed the intern documents thatís slowing things down.
Applying that analogy to our processor, suppose we have a processor thatís so fast that it can process data faster than it can be fed. Now, all of a sudden, itís not our processor holding things back, but the device that feeds the processor data. And what feeds the data to the processor? The memory.
Todayís Pentium 4 platforms are available with a choice of three types of memory; SDRAM, DDR SDRAM, and RDRAM. The former two are the more popular types (particularly in this community), and will likely continue to be the most popular for the near future, so those are the ones on which weíll focus today. The type of memory chosen directly affects not only the immediate performance of your system, but will affect the systemís ability to benefit from CPU upgrades in the future.
By using processors of various speeds, and paired with different memory combinations, this article will attempt to establish and quantify how well the Pentium 4 platform scales with clock speed at different memory speeds. This is not to say that memory is the only factor that affects scalability -- there are, in fact, potentially hundreds of factors at work, however the memory is usually far and away the largest.
Again, the intent here is not to dissect the architecture completely, but rather to offer some numbers and information that may surprise some readers, answer some questions, teach you a bit, or maybe just help you form new questions. Either way, consider this an Ďinterestí read.
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