Here is a breakdown of the filename:

conf t boot system flash flash:C2900-universalk9-mz.spa.157-3.m1.bin do wr

C2900-universalk9-mz.spa.157-3.m1.bin

Here is a breakdown of the filename:

conf t boot system flash flash:C2900-universalk9-mz.spa.157-3.m1.bin do wr C2900-universalk9-mz.spa.157-3.m1.bin