When SAS processes the program data vector, it typically
moves the data in one large operation rather than by individual variables.
When data is properly aligned (in 8-byte boundaries), data movement
can occur in as little as two clock cycles (a single load followed
by a single store). SAS moves unaligned data by more complex means,
at worst, a single byte at a time. This would be at least eight times
slower for an 8-byte variable.
Many high performance
RISC (Reduced Instruction Set Computer) processors pay a very large
performance penalty for movement of unaligned data. When possible,
leave numeric data at full width (eight bytes). Note that SAS must
widen short numeric data for any arithmetic operation. On the other
hand, short numeric data can save both memory and I/O. You must determine
which method is most advantageous for your operating environment and
situation.
Note: Alignment can be especially
important when you process a data set by selecting only specific variables
or when you use WHERE processing.