What is the onboard cache on a motherboard ?

[vinayag]

>> Onboard cache. Not really the most important feature, you may want to take note of the amount
>> of cache memory the motherboard you want to get has. As a rule of thumb, anything under 512K cache is
>> not worth it. Anything above 512K cache is very good, and just plain 512K is average.

I read this in one of the hardware sites and realize that I knew nothing about onboard cache when I got my Tyan trinity 400 !!!

What does onboard cache means ? What is the purpose ?

 

[Mday]

cache is MEMORY, almost just like RAM. the rule of thumb is a piece of crap, and is outdated. cache here refers to system cache. and onboard usually means L2 (level 2). onboard means on the motherboard. L1 (level 1) cache has always been part of the processor.

Back in the days of the pentium, the L2 cache came in a card that was inserted pretty much like an expansion card, into a specialized socket just for cache RAM. The thing about cache is that, it is MUCH faster than system RAM, and MUCH more expensive. Cache is made of SRAM which is hard to make. Sometimes motherboards have the cache soldered on. In this case, the cache operates at the speed of the motherboard, usually 66MHz. And for Pentium systems, that had L2 cache on the motherboard, the size is usually 512KB. Though some motherboards supported as much as 1MB of cache.

You may have read that the Pentium II processors have the L2 cache in the cartridge, or how the newer processors have the L2 cache onchip. This cache operates FASTER. And since the cache is part of the processor as a whole, the motherboards for Pentium II systems don't have onboard cache. This is what your motherboard is, that is, it has no need, nor can it support, cache on itself as it is part of the processor. Socket 370 is just basically a different variety of processor connection for the latter type of processor i mentioned which has the cache on the chip.

enough of the background, why is cache important? well, cache is RAM.

you have several levels of storage of data on your computer. the slowest is your drives, HDD or CD\DVD-ROM or floppy. HDD is for permanent storage where your data and programs are stored. Then you have your system RAM, this is where your 128MB or whatnot comes in. when you access that data, or open that program for use, the data moves to the much faster system RAM.

Now, what about L1 or L2? In order for the computer to "process" data or execute a program, it has to go to the processor. Since system RAM is MUCH SLOWER than the processor, the processor has it's own L1 cache (which is RAM also remember, just MUCH faster than your system RAM) so it can store smaller amounts of data to be "processed" much faster due to the speeds over system RAM. With L2, well, the processor has a larger reservoir of data to draw from which is faster than system RAM. it is also important to know that data is exchanged constantly, so whatever you use, is whatever is stored in RAM, be it system, L1 or L2.

 

[Mday]

a note about L3: it exists. on pentium systems, the L2 cache is on the motherboard. What if there was a processor that can use the same socket as the pentium that had onchip L2 cache? well, you get L3. AMD's K6-3 processor was such a processor, and could be used on a pentium (socket 5 or socket 7) type socket. But this type of motherboard was not designed for the pentium, so the socket was called super 7 because the FSB (front side bus) is 100MHz, as opposed to 66MHz.

RAM speeds are measured in ns (nanoseconds), which can be converted to MHz.

As for the 512K thing you mentioned, it is outdated because speeds of L2 cache has become MUCH faster since with the beginning of the Pentium 2 (cache part of the processor), L2 cache ran at 1/2 the speed of the processor which meant it was MUCH faster than your onboard cache. The size of this cache was 512KB keeping in line with the predecessor Pentium systems with 512KB of cache on the motherboard. THEN, the celeronA processors came out, with 128KB of L2 cache, which RAN at FULL processor speed. So for a given PII or celeronA rated at the same MHz, the cache of the celeron was 4 time smaller, but ran twice as fast. This ratio made the performance of the celeronA virtually identical to the PII. Now the new Pentium 3s have full speed onchip L2 cache, 256KB of it. Note, the ratio is just for the celeron and pentium2\3, it also depends on how the cache is actually implemented.

And why is 512K of cache is outdated. it's not only capacity anymore, it's speed too.

and more is better. Intel has their Xeon line of processors with 1 MB of cache or more, which cost several thousand dollars. But these processors have the same core, which means other than the cache, the processors are IDENTICAL. more RAM means being able to handle more data more efficiently.

 

[Mday]

without cache, your system may just slow down A LOT. the same can be said with less system RAM. and don't even ask about having NO L2 cache and barely any RAM running today's software...

 

[StanTheMan]

Mday is correct. The difference between original celeron (Covingto core) with Celeron A (Mendocino core) is great when they are runnong at the same speed. It was just bcos the celeron A has 128 kb L2 cache.