The standard without a memory chip is about 150K of memory for data and I/O. For more data storage you have to add a memory chip on the processor board to increase its capacity.
On the 5550 L1 processors you have 3 memory chip options
M1 - ~500K
M2 - ~1000K
M3 - ~2000k
One other note... the L1 processors will only work up to firmware revision 13. After that these processors were phased out by AB.
If you are looking to expand memory on one of them, I'd strongly suggest taking advantage of the AB Trade-up program, and swapping the 5550's for a 60 series processor.