Mitsubishi Electric MELSEC-Q00U(J)CPU User Manual page 322

(d) File size (size for saving)
The size of the operation history file can be changed in the RAS tab of the PLC parameter. (
Appendix 1.2.4)
The setting range is from 1 to 1024K bytes.
If the storage size exceeds the specified size, histories are deleted in order from the oldest one and the latest
one is stored.
The following table lists each element to be stored in the operation history file and its size.
File header size
Operation history management information size
Size per operation history
*1 Since detailed information may differ depending on the operation history to be saved, the size per operation history is
variable.
The number of the operations to be saved in the operation history file differs depending on the operation type to
be saved. The following provides examples of the registrable number of operations when the size of the
operation history file is the default of the function setting (128K bytes).
When programs (program name: 8 characters (12 characters including a period and extension)) are
Ex.
continued to be written to the CPU module
[Calculation formula]
128 [K bytes] = 128 [bytes] × 1024 = 131072 [bytes]
131072 [bytes] - (64 [bytes] + 12 [bytes]) = 130996 [bytes]
130996 [bytes]  72 [bytes] = 1819 [operations]
Up to 1819 operation histories (2000:Write File) can be registered.
When one point of M0 (bit) is continued to be written with SLMP Write command to the CPU module
Ex.
[Calculation formula]
128 [K bytes] = 128 [bytes] × 1024 = 131072 [bytes]
131072 [bytes] - (64 [bytes] + 12 [bytes]) = 130996 [bytes]
130996 [bytes]  64 [bytes] = 2046 [operations]
Up to 2046 operation histories (1000: Write Device) can be registered.
320
Element name Size
64 bytes (fixed)
12 bytes (fixed)
*1
40 bytes minimum (variable)
Page 441,