Answer / navdeep

Both are different series of PLC with major difference of
Memory capacity, both have same programming software of
Simatic Step 7, Input Output range vary as per version or
model of PLC used, the memory size of PCMCIA card in both
PLC vary, Data Transmission speed varies in both the PLC,
S7 300 plc are small in size or compact while S7 400
requires separate PSU with the CPU they are bigger in size
compared to s7 300.

Answer / taj

Siemens rates the S7-300 as a medium level PLC, and the S7-400 as a high-level PLC. So there are differences in work memory, processor speed, number of communication links and I/O connectivity.
First point, the S7-400 family is rack-based (Multi-pin backplane linking all modules, from power supply to I/Os) whereas the S7-300 is a bus-linked platform (a serial connector links all modules). So essentially the physical layout limits the S7-300 back[plane exchanges to MPI speeds (187,5 Bits per second), whereas the S7-400 uses parallel connections over the backplane rack, permitting higher exchange rates, and a higher module-density.
Second point, the form factor of the S7-300 is smaller, more compact than the S7-400, so this is something to take into account if space is a premium (inside a small machine panel, for example).
Now, the higher S7-300 CPUs (especiatlly for the new S7-317 and S7-319)have specs that approach (and sometimes pass) the specs of lower end S7-400 CPUs, so the distinction is starting to blur.

Answer / guna

S7-300 plc is a mid end plc rated by the Siemens, This
rating is depends on so many constraints but main
consideration on Number of I/O's & Instruction set, No.of
baud-rates, Cost per module. it works on the Simatic
manager driver software. it is available in compact and
modular types. this needs separate flash memory cards
(Removable)in cpu memory to store the data.

S7-400 is a high end plc means its capacity is larger when
compared to s7-300 in all the ways like technically and
physically. it can also work on the simatic manager. S7-400
is also called as DCS (distributed control systems) which
works on the driver software of PCS-7. its memory capacity
is above 64mb(very high).

the hardware configuration of both the plc types differs
a lot.

Answer / guest

s7-300 means we can able to develop a logic upto 300 and
simultaneously 500

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