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Question about AMD Laptops L2 Cache

N

narmak

Junior Member
I'm not the most technically advanced, but I know that alot of the AMD notebooks, for exmaple the AMD 3800+ has a FSB of 2000mhz, but it only has a 512kb cache. While a Centrino 1.86 has a 533MHZ FSB, but the cache is 2mb. Is it just not possible for an AMD to have a 2mb cache? Does the higher AMD FSB make up for the difference?

It just confused me when I was looking at those specs. Any help would be GREATLY appreciated. Thanks.
 
On AMD K8 chips, extra cache doesn't make for a huge difference in most cases because if it needs to access data bigger than what the cache can hold, it can go to ram. K8 chips can get data off ram very quickly because of the on-die memory controller. If a Pentium M needed to get data off ram, data would run through the northbridge, contributing to more latency.
 
While having more cache will be better (even if its a little bit), it boils down to real estate. To keep costs down, chip makers want the most cpus per wafer so that means smaller cpus and by extension, smaller feature size (130nm -> 90nm -near future> 65nm). On die cache takes up a lot of space and can also decrease yields (more complex design = more things that can go wrong in its manufacturing) and that space could be better used. AMD chips will perform better theoretically with more cache but the increase probably cannot be justified by the cost and yield factors involved.

As for your other point, AMD cpus use HyperTransport (the 2000 MHz number) and not a FSB. That is slightly (and I use the term loosely) different from FSB. I suggest looking on the AMD website to learn about HT vs FSB.
 
Originally posted by: narmak
I'm not the most technically advanced, but I know that alot of the AMD notebooks, for exmaple the AMD 3800+ has a FSB of 2000mhz, but it only has a 512kb cache. While a Centrino 1.86 has a 533MHZ FSB, but the cache is 2mb. Is it just not possible for an AMD to have a 2mb cache? Does the higher AMD FSB make up for the difference?

It just confused me when I was looking at those specs. Any help would be GREATLY appreciated. Thanks.
Click to expand...


Cache greatly increases the cost to produce a chip.
Plus, a larger cache size can also mean more latency to retrieve data from the cache, if cache size can't be increased without increasing latency, then there isn't too much benefit to increasing it.

BTW, hypertransport runs at 2ghz, its the entire platform's bus speed though, not just the cpu, everything on the motherboard taps into that bus.
 
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