What is the diffrence between S7 200 & S7 300 plc?

well there are many differences in S7200 and S7300.  But so far to my knowledge S7200 is referred to as a micro PLC because of it small size. the S7200 is brick design which means that the power supply and I/O are on board. S7200 can be used on smaller, stand alone application such as Elevators, crush machine, car washers, can also be used on little complex machine such as bottling and packing machines. 

while is used on more Complex machine that support greater number of I/O points. S7300 is modular and Expandable. The I/O and power supply consist of separated modules connected to CPU. it is chosen often by the industries that they have future expansions plans or not. S7300 is more costly and large in size compare to S7200.

i am sorry for my spellings mistakes and late reply as i was busy some where else.

I am Afraid, i dont have knowledge of this 

S7200 & S7300 both are Siemens PLC.S7200 is obsolete version of Siemens Required Step 7 microwin Software for Programming.  S7300 is latest then S7200 Required Sametic Step 7 for Programming.

the main diffrent between them it size, so I agree with all answers.

S7-200 is a (microcontroller) PLC for small applications and can only be programmed via special SW and small instruction set with low memory. you can not able to expand the reck of extra I/O module. S7-200 has limited timer (On delay/off delay and pulse).S7-300 is for the low-end and mid-end performance applications (Compact modules). you can able to expand the reck of extra I/O module with central control main PLC. S7-300 has the addition of " retentive on delay and off delay timers" which provides so much specific and easiest way to programe on it.

There is lot more differences on the behalf of technical terminology. like CPU, operating software , Memory bits, Code function , clock memory and flash memory and so on.