Mitsubishi Electric MELSEC iQ-R Series - Defragmentation of Drive Memory

15 QnACPU DEDICATED COMMANDS
15.2 Defragmentation of Drive Memory
289
15
15.2 Defragmentation of Drive Memory
An external device performs the following functions for other station QnACPU drive which stores parameters and program
files that the sequence programs are written.
Read drive memory usage status
Check the usage status of the drive memory (cluster usage status) of the specified drive.
Defragment drive memory
When the valid data written in the drive memory is not consecutive, increase the consecutive free area in cluster unit by
defragmentation.
A cluster is the minimum unit when files are stored to drive memory (such as memory card) and the memory
containing data is managed by FAT
*1
.
The size of one cluster of each QnACPU drive is as follows:
• Internal memory : 4096 bytes
• Other memory : 512 bytes
For example, if a data less than 512 bytes is written to a memory card, one cluster of drive memory is used to
write the data.
If 513 to 1024 bytes of data are written, two clusters of drive memory is used to write the data.
*1 An abbreviation for 'File Allocation Table'. A table used by the operating system to manage the location of files on the drive memory.
■Images of drive memory defragmentation
: Cluster in not used (empty), : Cluster is being used (valid data is written in it)
• Before drive memory defragmentation

• After drive memory defragmentation
*1 16th cluster from the head cluster
*2 First cluster
*3 Last cluster
Cluster b15 b14 b13 b12 b11 b10 b9 b8 b7 b6 b5 b4 b3 b2 b1 b0
First 16 clusters 
*1

*2
  
 
  
 
  
Last 16 clusters 
*3
 
Cluster b15 b14 b13 b12 b11 b10 b9 b8 b7 b6 b5 b4 b3 b2 b1 b0
First 16 clusters 
*1

*2
 
 
 
 
 
Last 16 clusters 
*3
