Configuring Entire OS vs Changes-Only Downloads and Resolving Grayed-Out Options in PCS 7

In SIMATIC PCS 7, the download option 'Entire OS' is disabled or grayed out when WinCC Runtime is actively running on the target Operator Station, because an entire download completely overwrites the runtime project database files (.mcp and SQL databases), which cannot occur while database engines hold active file locks. Conversely, 'Changes only' is grayed out if the OS project was never compiled, if an 'Entire Compilation' was executed, or if structural changes (such as alarm logging schema or picture tree restructuring) mandate an initial Entire Download. To enable Entire OS download, deactivate WinCC Runtime on the target OS and close WinCC Explorer; to enable Changes-only download, compile the OS with the 'Changes' option and ensure the project was previously downloaded entirely.

Executive Summary

Maintaining continuous human-machine interface availability while deploying control updates requires a precise understanding of the download mechanisms in SIMATIC PCS 7. Engineers attempting to update an OS Server or Single Station frequently find either the Entire OS or Changes download options unexpectedly disabled in the PLC Download dialog. Attempting to force an entire download while the plant is in operation risks catastrophic visibility loss, while being unable to download online changes halts routine commissioning. This article explains the architectural differences between Entire and Changes downloads, outlines the prerequisites for each transfer mode, and provides verified operational sequences for redundant server maintenance.

Architecture and Fundamental Mechanics

WinCC Database Locking, OS Compile Modes, and Download State Machines in PCS 7:

Architecture of 'Entire OS' Download:
An Entire OS download transfers the complete WinCC project directory: CS (Configuration Studio) project file, Master SQL databases (<Project>.mdf/.ldf), runtime templates, graphics (.pdl), scripts, and configuration archives.
Runtime Lock Constraint: When WinCC Runtime is active, Microsoft SQL Server attaches the project databases and holds exclusive operating system write locks. Any attempt to overwrite active .mdf/.ldf files results in Windows sharing violations. Therefore, PCS 7 automatically disables the 'Entire OS' option if WinCC Runtime or WinCC Explorer is detected open on the target.
Architecture of 'Changes' Download (Delta Download):
Changes-only download transfers only modified graphic pictures (.pdl), updated tag definitions, and new alarm messages into the running WinCC database via real-time online SQL replication scripts without interrupting operator visualization.
Prerequisites for Changes Download:
1. The target OS must have previously received an 'Entire OS' download of the exact base project version.
2. The OS was compiled with the Changes scope (not Entire OS compile).
3. No structural changes occurred that violate online delta transfer rules (e.g. modifying computer name, changing redundancy partner assignments, or modifying OS Project Editor basic screen layouts).
Redundant Server Staged Download Workflow:
For redundant OS servers, an Entire Download must NEVER be executed simultaneously on both servers.
The procedure mandates a phased sequence: deactivate Standby Server -> download Entire OS -> activate Standby Server -> wait for archive redundancy synchronization -> switch clients -> repeat on Master Server.

Step-by-Step Implementation Procedure

How to Enable and Execute an 'Entire OS' Download:
* On the target OS Server / Single Station, click Deactivate in WinCC Explorer to shut down WinCC Runtime cleanly.
* Close WinCC Explorer and all Siemens engineering applications on the target machine.
* On the Engineering Station in SIMATIC Manager, select the OS object.
* Select menu PLC > Download.
* Confirm that Entire OS is now selectable.
* Click OK to execute the full transfer.
How to Enable and Execute a 'Changes Only' Download:
* In SIMATIC Manager, right-click the OS object and select Compile.
* In the OS Compilation Wizard, select Changes (never select 'Entire' if you intend to do an online delta download).
* Complete compilation; confirm that compilation finishes without errors.
* Right-click the OS object, select PLC > Download, and select Changes.
* Click OK; observe the delta download complete while WinCC Runtime continues running on the target station.
Recovering When 'Changes' Is Unexpectedly Grayed Out:
* If 'Changes' is grayed out despite compiling changes, check if an 'Entire compilation' was run previously. An Entire compilation resets the delta tracking pointer and forces an initial Entire Download.
* Check if the project was restored from a foreign backup without an initial baseline download.
* For redundant servers, plan a staged download maintenance window to re-establish the baseline.

Verification

During a Changes download, observe that WinCC Runtime on the target OS remains active and alarms continue to update.
Confirm that newly added graphic elements or tag changes appear on operator screens within 10 seconds of download completion.
Verify that the SIMATIC Manager download status window reports 'Download of changes completed successfully'.

Limitations and Operational Precautions

Executing an 'Entire OS' compile permanently disables 'Changes' download until a full offline Entire Download is performed. Certain changes—such as modifying the computer name, changing communication drivers in Tag Management, or updating basic APL faceplate templates via OS Project Editor—strictly require an Entire Download.

Engineer FAQ

Why is 'Entire OS' download grayed out?

WinCC Runtime is currently running on the target OS computer. Deactivate runtime and close WinCC Explorer to enable it.

Why is 'Changes only' download grayed out?

An Entire compilation was executed, or the project was never downloaded entirely to establish the delta tracking baseline.

Can I download changes to redundant OS servers while the plant is running?

Yes, Changes download is designed to update running redundant OS servers without interrupting operator supervision.

Does compiling 'Entire OS' stop runtime?

Compiling does not stop runtime, but it forces the next download to be an 'Entire OS' download, which requires stopping runtime.

What happens if a Changes download fails midway?

WinCC rolls back the transaction. You must rectify the error and re-download changes or plan a staged entire download.

Technical References

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Configuring Entire OS vs Changes-Only Downloads and Resolving Grayed-Out Options in PCS 7