dcba, dcbz, dcbt, dcbtst cache control instructions in PowerPC

dcba - Data Cache Block Allocate

dcbz - Data Cache Block set to Zero

dcbt - Data Cache Block Touch

dcbtst - Data Cache Block Touch for Store

are called data-cache hint instructions. These instructions are used to improve the memory performance by avoiding cache miss. With these instructions, the cache lines corresponding to memory locations that are likely to be accessed in the near future can be allocated speculatively to avoid cache-miss. For example, with dcbt and dcbtst instructions, if the byte specified by the effective address (EA) is cacheable and is not currently cached by the data cache, the cacheline containing that byte is loaded into the data cache from main memory.

dcbt and dcbtst instructions are further optimized to dcba and dcbz instructions where the cache lines are allocated for the effective address (EA) without copying data from system memory where the contents of the main memory are no longer needed or the memory block can be initialized to zero.