The structure of a .COM is somewhat simplified and possesses less functionality. A .COM program may occupy only one segment. Thus it may not exceed 64 kb in size. The stack of a .COM is automatically created by the assembler so the programmer does not define a stack in a .COM program. Since a .COM may not have a separate data segment, data declarations in a .COM are embedded in the code.
Most programmers locate the data declarations at the begining of the program.
This means that the first instruction in a .COM must normally be a jump around the data declarations since we do not want the system to interpret them as code and try to execute the data. The former approach is preferred. Do not code a stack segment since this will be handled automatically by the assembler. Locate data declarations near the start of the code. Make the first instruction a jump around the data declarations to the actual start of program code.