Does PHP has built in caching mechanism that can handle many small changes?

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http://stackoverflow.com – My programs use usual file system to do caching. The amount of disk read and write is so phenomenal that I got to use SSD But SSD don't have many spaces. I wonder if PhP has a a caching mechanism that say cache data in memory and write only ocassionally? I think I read that somewhere but then couldn't find it. I checked memcached Actually it doesn't. The problem is memcached would speed up read. I got huge WRITE. Not huge read. (HowTos)