Cache Size for HDD, what does it mean?

The larger the cache the better. Cache is MUCH faster than the hard drive.

Data is read and written to and from cache (hopefully). Then sent to the HD or to RAM.

The more cache means more data that can be accessed quickly. As in orders of magnitude faster.

 

"They" say bigger is better, but is 32MB cache 4 times better than 8MB cache?

 

Unfortunately, No. If you plot out the performance of the same drive with different cache values, it's not linear. But larger values do help, and it can be simplified to "get the largest available for the capacity".

Another way to look at it, is cache/GB. For example, WD's RE3 line. The 250 & 320GB variants have 16MB of cache, while the 1TB model has 32MB. And the smaller drives do run a little quicker. Other issues such as platter count are also factors, as the smaller drives are singles.

WD's datasheets show this in the specs, as does independent testing. Personally, I take what I can get.