I use the Keil C51 V5.02

If you are a experienced assembler programmer, your C programs should need only about 5..20% more code space as on programming in assembler.

If you not so experienced on assembler, a C program should need less program memory and looking on the assembler listing can teach you many tricks, how efficient the C compiler works on the 8051.

Be aware, use never the large model. Always use the small model and place only large data into the xdata space.


Peter