VTAM® uses buffer pools to control the handling of data: VTAM control blocks, I/O buffers, and channel programs that control the transmission of data. Each buffer pool handles storage for a different VTAM service; therefore, the needs of your network will determine which buffer pools are used the most. After you determine which buffer pools are the most important to your system, you may want to change the sizes of some of the buffer pools.

When you set a buffer pool size, you are reserving storage for use only by that buffer pool. If you specify buffer pools that are larger than necessary, you are setting aside storage that is not being used. The storage is being wasted when it could be used in other areas.

When you set a buffer pool size that is too small, VTAM will reach the buffer pool limit and will then dynamically allocate more space in the buffer pool. When the current need is satisfied, VTAM will then dynamically deallocate space in the buffer pool. Specifying small buffer pools conserves storage, but can cause frequent CPU use for expansion and contraction. For information about types of buffer pools and buffer pool allocation, see Buffer pools.