The help file of RS logix 5 describe it as follows.
The following list describes the different data table file types. Default data table file types 0-8 cannot be redefined.
File # - Type File Description Comments
O0 - Output This file stores the state of output terminals for the controller. --
I1 – Input This file stores the state of input terminals for the controller. --
S2 - Status This file stores controller operation information useful for troubleshooting controller and program operation. Status file 2 is fixed at 32 words for PLC-5/10, -5/12, -5/15, and -5/25 processors and at 128 words for PLC-5/11, -5/20, -5/30, -5/40, -5/40L, -5/60, -5/60L, and -5/80 processors.
B3 - Binary Bit This file stores internal relay logic. This file can be 1,000 words maximum.
T4 - Timer This file stores the timer accumulator and preset values and status bits. T4 is the default file number. For this file type, you can assign any file number from 3 thru 999. This file cannot exceed 1000 structures.
C5 - Counter This file stores the counter accumulator and preset values and status bits. C5 is the default file number. For this file type, you can assign any file number from 3 thru 999. This file cannot exceed 1000 structures.
R6 - Control This file stores the length, pointer position, and status bits for specific instructions such as shift registers and sequencers. R6 is the default file number. For this file type, you can assign any file number from 3 thru 999. This file cannot exceed 1000 structures.
N7 - Integer This file is used to store numeric values or bit information. N7 is the default file number. For this file type, you can assign any file number from 3 thru 999. This file can be 1,000 words maximum.
F8 - Floating Point This file stores a # with a range of -3.40282347e38 to -1.1754944e-38 and 1.1754944e-38 to 3.40282347e38. F8 is the default file number. For this file type, you can assign any file number from 3 thru 999. This file can be 1,000 float words (32-bit words) maximum.
A(3-999) - ASCII This is an ASCII data storage file. This file can be 1,000 words maximum.
D(3-999) - BCD This is a BCD data storage file. This file can be 1,000 words maximum.
BT(3-999)
Block Transfer Used to store control data for the BTR (Block Transfer Read) and BTW (Block Transfer Write) instructions. This file cannot exceed 1000 structures. (Available only with these processors)
MG(3-999)
Message Used to store message data for the Message instruction. Each MG file can be 585 structures maximum. (Available only with these processors)
PD(3-999)
PID This is a PID (Proportional, Integral, Derivative) storage file. Each PD file can be 399 structures maximum. (Available only with these processors)
SC(3-999)
SFC Status Used to store SFC (Sequential Function Chart) status data. This file cannot exceed 1000 structures. (Available only with these processors)
ST(3-999)
ASCII String Used to store string data for ASCII instructions. Each ST file can be 780 structures maximum. (Available only with these processors)
CT(3-999)
ControlNet Message Used to store data for ControlNet instructions. Each CT file can contain a maximum of 1000 elements. (Available only with Control Net processor)
MTX(3-4095)
Mutex Used to provide an exclusive access handshaking mechanism between two or more cooperating asynchronous processes. Each MTX file can contain a maximum of 4096 elements.
4 words/element. (Available only with the SoftLogix 5 controller)
EVT(3-4095)
Event Automatic event. Lets you create user defined events that send a signal to an external program. Each EVT file can contain a maximum of 4096 elements. 4 words/element. This is an edge-triggered auto-resetting event mechanism. (Available only with the SoftLogix 5 controller)
EVTM(3-4095)
EVTM Manual event. Lets you create user defined events that are broadcast to all external programs that interface with the SoftLogix 5 engine. In addition, you can use EVTM events to poll for incoming messages from an external program. Each EVTM file can contain a maximum of 4096 elements. 4 words/element. This is a level-triggered auto-resetting event mechanism. (Available only with the SoftLogix 5 controller)
L(3-4095)
Long Used to provide a 32-bit signed integer. Each L file can contain a maximum of 4096 elements. 2 words/element. The L file type cannot be used in an indirect address. (Available only with the SoftLogix 5 controller)
DF(3-4095)
Double Precision Float Stores a number with a range of -1.7976931348623157e308 to -2.2250738585072014e-308 and 2.2250738585072014e-308 to 1.7976931348623157e308Bit addressing is disallowed. Each DF file can contain a maximum of 4096 elements. 4 words/element. (Available only with the SoftLogix 5 controller)
Rockwell Software Inc., 1997, 1998, 1999, 2000