Following the move to the new Publish-Subscribe infrastructure with Version 7.0, a number of customers were adversely affected by a change in the way the product behaves in respect to Block Writes. This change was generic to the driver interface and specific issues have been raised with in regard to HITACHI, MODBUS and OPC, however other drivers may also have been affected.
In Version 7.20 changes have been made to the way that writes are performed at the I/O Server in order to restore the pre-V7.0 behavior.
These changes will result in a similar level of blocking as occurred in previous versions. It does not confirm that writes will be blocked, but it is more than likely that they will be if they are initiated close enough together.
This will also allow use of the re-instated Citect.ini parameter [IOServer]BlockWrites in order to choose whether to use the Block Writes functionality.