A data cache can have as many as 4 separate pools.
When initially created a data cache will always have a single pool where the pool's IO size is the same size as the dataserver's pagesize (@@maxpagesize) (eg, a dataserver with @@maxpagesize=16K IO will always have a 16K IO pool in every data cache).
The DBA can then add up to 3 more pools (sizes: 2x @@maxpagesize, 4x @@maxpagesize, 8x @@maxpagesize) to a data cache.
data cache changes (eg, cache size, number of partitions, cache replacement policy) are made with the sp_cacheconfig stored proc.
pool changes (eg, pool size, wash marker, APF) are made with the sp_poolconfig stored proc.
A data cache's memory is allocated across the 1-4 pools that make up the data cache (ie, data cache memory = sum(pool memory)).