Resolving WinAC RTX Boot Options Complete Removal After Uninstall

1. Problem Overview

Siemens WinAC RTX (Windows Automation Center – Real-Time eXtension) installs a real-time kernel subsystem on the host PC that runs side-by-side with Microsoft Windows. After installation, the Windows boot loader is modified to present an additional boot entry, typically labeled "Windows XP/RTX Shared" or "Windows 7/RTX Shared," that boots the operating system with the IntervalZero RTX real-time HAL enabled. The WinAC RTX engine, the SoftPLC runtime, and any configured PC stations then communicate with the I/O over PROFIBUS or PROFINET through the real-time layer.

When an engineer removes the WinAC RTX software through the standard Windows Add/Remove Programs (Windows XP) or Programs and Features (Windows Vista/7/8/10/11) control panel, the application binaries, STEP 7 PC station configuration, and the RTX runtime drivers are removed, but the boot menu entry persisted in the Windows boot configuration is not removed automatically. The result is a stranded boot option that, if selected, either boots into a non-functional RTX environment (causing a hang, BSOD, or repeated rollback) or requires the operator to wait out the timeout to reach the default Windows desktop.

The issue affects all WinAC RTX product versions, including 3.1, 4.0, 4.1, 4.2, 2005, 2008, 2010, and 2010 SP2. The boot mechanism differs between Windows XP (boot.ini) and Windows Vista and later (BCD store), so the corrective procedure depends on the host operating system in use.

2. Root Cause Analysis

WinAC RTX relies on the Ardence / IntervalZero RTX real-time extension, a kernel-mode HAL augmentation that turns Windows into a deterministic real-time platform. The RTX installer performs three actions that survive an Add/Remove uninstall:

1. Boot loader modification. On Windows XP, the RTX installer appends a new [operating systems] stanza to C:\boot.ini and adjusts the timeout= value. On Windows Vista and later, the installer writes a new BCD object in the Boot Configuration Data store. Uninstalling the WinAC RTX application packages removes the RTX user-mode DLLs and the SoftPLC service but does not roll back the boot loader change.
2. Driver registration. The RTX HAL driver (RtxSrv.exe, rtxSer.exe, and several rtX*.sys kernel drivers) is registered in HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services. The uninstaller removes the user-mode executables but the service registry keys are typically left in place.
3. STEP 7 PC station integration. The PC station project in the SIMATIC Manager or TIA Portal retains the WinLC RTX slot. Re-installation is not required to remove the boot option, but the engineer should clear the PC station configuration if a different controller will replace WinAC RTX.

Because the boot loader entry is the most user-visible side effect, this article focuses on the boot.ini and BCD removal procedure, then walks through the residual driver and registry cleanup that produces a fully reverted Windows installation.

3. Prerequisites

Before starting the boot entry removal procedure, confirm the following:

• Local administrator account on the WinAC RTX host. The boot configuration store and the C:\boot.ini file are protected system objects.
• Knowledge of the host operating system. Check winver or msinfo32 to confirm Windows XP SP3, Windows Vista, Windows 7, Windows 8/8.1, Windows 10, or Windows 11.
• Original WinAC RTX installation media or download, referenced from the WinAC RTX 3.1 Overview PDF (Siemens Support, attachment 12099246) if re-installation is required as a recovery path.
• Boot media (Windows installation DVD/USB or a manufacturer recovery partition) in case a no-boot condition is introduced.
• Empty USB key or network share for backing up the boot.ini file or exporting the BCD store.

Identify the currently selected boot entry before editing. From an elevated command prompt run bcdedit /enum all (Windows Vista and later) or open C:\boot.ini in Notepad (Windows XP). Mark which stanza is the default Windows installation and which was added by the RTX installer.

4. Uninstalling the WinAC RTX Application

Step 1 below is the only step the OEM-supplied uninstaller performs. Steps 2-8 must be executed manually to clean up the boot entry, drivers, and registry residue.

1. Remove the WinAC RTX application. Open Control Panel → Add/Remove Programs on Windows XP, or Settings → Apps → Apps & features on Windows 10/11. Locate SIMATIC WinAC RTX (or Windows Automation Center RTX) and select Uninstall. The Siemens uninstaller removes the SoftPLC runtime, the WinLC RTX slot type, the PC station templates, and the STEP 7 integration plug-ins.
2. Reboot once to complete the application removal. Note that the RTX boot option will still be present.

Reference: WinAC RTX 3.1 Overview, Siemens Support attachment 12099246, sections on Add/Remove Programs workflow.

5. Removing the RTX Boot Entry on Windows XP (boot.ini)

Windows XP stores boot configuration in a plain-text file at C:\boot.ini. The file is hidden, read-only, and system. To edit it, use the following procedure.

1. Open an elevated command prompt (Start → Run → cmd → OK, or right-click Command Prompt and select Run as administrator).
2. Clear the read-only attribute and back up the file:

   attrib -r -h -s C:\boot.ini
   copy C:\boot.ini C:\boot.ini.bak

3. Open the file in Notepad:

   notepad C:\boot.ini

4. Identify the RTX stanza. A typical post-install boot.ini reads:

   [boot loader]
   timeout=30
   default=multi(0)disk(0)rdisk(0)partition(1)\WINDOWS
   [operating systems]
   multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows XP Professional" /noexecute=optin /fastdetect
   C:\RTX\RTXBOOT.SYS="Windows XP/RTX Shared" /fastdetect /rtxport=0xD000 /rtxirq=5 /rtxmode=rtxhal

   The second [operating systems] entry is the RTX shared kernel boot. It references RTXBOOT.SYS in C:\RTX\.
5. Delete the RTX line entirely. Be careful not to alter the Windows XP Professional entry.
6. Adjust the timeout from 30 to a value appropriate to single-boot operation. Microsoft documentation and forum guidance suggest 3 seconds as a practical minimum. The [boot loader] section becomes:

   [boot loader]
   timeout=3
   default=multi(0)disk(0)rdisk(0)partition(1)\WINDOWS

7. Save and close Notepad, then restore the file attributes:

   attrib +r +h +s C:\boot.ini

8. Reboot. The boot menu should no longer appear.

To revert the timeout to a fast single-second display without deleting the RTX line (the workaround suggested for situations where the engineer cannot edit the file), the same procedure applies with timeout=1. This is a cosmetic mitigation only; the stale RTX stanza remains and will fail to boot if selected.

6. Removing the RTX Boot Entry on Windows Vista / 7 / 8 / 10 / 11 (BCD)

From Windows Vista onward, the boot configuration is stored in the BCD (Boot Configuration Data) registry hive at \EFI\Microsoft\Boot\BCD (UEFI) or in a file at \Boot\BCD (legacy BIOS). Editing is performed with bcdedit.

1. Open an elevated command prompt. Press Win+X, then select Terminal (Admin) or Command Prompt (Admin). On Windows 7 use Start → type cmd → Ctrl+Shift+Enter.
2. Export the BCD as a safety backup:

   bcdedit /export C:\BCD_Backup\bcd_backup

   If the command returns The store export operation has failed, the path does not exist. Create the directory first: mkdir C:\BCD_Backup.
3. Enumerate boot entries to identify the RTX object:

   bcdedit /enum all

   The RTX entry is typically labeled Windows 7/RTX Shared or Windows XP/RTX Shared. Note the identifier GUID, for example {c3a8e8a1-1f3a-4f7e-9d2b-2c7c0a4e1f01}. The device and path fields will reference \RTX\RTXBOOT.SYS or an RTX boot loader file.
4. Delete the RTX entry:

   bcdedit /delete {c3a8e8a1-1f3a-4f7e-9d2b-2c7c0a4e1f01}

   Replace the GUID with the identifier noted in step 3. If the entry is the default boot, BCD will not allow deletion until another entry is set as default; switch the default first:

   bcdedit /default {current}

5. Adjust the boot menu timeout. By default Windows 7+ uses a 30-second menu. To disable the menu entirely:

   bcdedit /timeout 0

   To set a 3-second menu, use bcdedit /timeout 3. The boot menu can also be controlled from System Configuration (msconfig) on the Boot tab.
6. Verify with bcdedit /enum that only the default Windows installation remains.
7. Reboot and confirm the boot menu is gone.

On UEFI systems with Secure Boot, bcdedit operates against the firmware-resident BCD. The same commands apply; no separate UEFI variable cleanup is required for the WinAC RTX entry.

7. Removing the IntervalZero RTX Subsystem

After the boot entry is removed, residual RTX drivers and services may still be installed. Clean them up in the following order.

1. List RTX-related services from an elevated command prompt:

   sc query state= all | findstr /I "RTX"

   Typical service names are RTX, RTXSer, RtxTimer, and RTXSync.
2. Stop and delete each service:

   sc stop RTX
   sc delete RTX
   sc stop RTXSer
   sc delete RTXSer

3. Remove the RTX installation directory, default locations:
   • Windows XP: C:\RTX and C:\Program Files\RTX
   • Windows 7+: C:\Program Files\Ardencia\RTX or C:\Program Files (x86)\IntervalZero\RTX depending on version
   If Windows reports the directory is in use, the RTX service is still running. Re-run the sc stop command and retry.
4. Remove RTX driver files from %SystemRoot%\System32\drivers\: rtX*.sys, rtxhal.sys, rtxport.sys. The del command will require the service to be deleted first.

8. Registry and Configuration Cleanup

The following keys may contain residual WinAC RTX configuration. Back up the registry (File → Export in regedit) before editing.

• HKEY_LOCAL_MACHINE\SOFTWARE\Siemens\WinAC RTX — version, install path, license fingerprint.
• HKEY_LOCAL_MACHINE\SOFTWARE\Ardence or HKEY_LOCAL_MACHINE\SOFTWARE\IntervalZero — RTX subsystem settings.
• HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\RTX* — service registrations (also removed by sc delete).
• HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\WinPE — not used by RTX, skip.

Use regedit to navigate to each key, right-click, and select Delete. If a future WinAC RTX installation is anticipated, skip registry removal and re-install over the existing structure to preserve any leftover PC station projects.

9. STEP 7 PC Station Reconfiguration

If the PC station previously hosted WinLC RTX (Slot 4 of the PC station configuration in SIMATIC Manager or TIA Portal), the slot is now empty. To prevent NetPro / Topo errors during compile, do one of the following:

• Reinstall WinAC RTX and re-import the PC station from the S7 project backup. Use the WinAC RTX 3.1 Overview for installation workflow.
• Replace the slot with a different controller (for example, a software controller on ET 200SP or a hardware S7-1500 attached via PROFINET) and re-assign any tags previously bound to WinLC inputs/outputs.
• Remove the slot from the PC station if the engineer is decommissioning the SoftPLC. The PC station can then host an HMI runtime or OPC server only.

10. Verification Procedure

1. Boot menu verification. Reboot the host. Confirm the boot menu does not appear (or appears for at most the configured timeout) and that Windows boots directly to the default installation.
2. Service verification. From services.msc confirm no RTX services are present. Run sc query state= all | findstr /I "RTX" and verify the command returns no results.
3. Driver verification. Open Device Manager → View → Show hidden devices and confirm no RTX HAL, RTX Sync, or RTX Timer entries are listed under System devices or Non-Plug and Play Drivers.
4. Filesystem verification. Confirm C:\RTX (or the IntervalZero install path) is removed and that no rtX*.sys files remain in %SystemRoot%\System32\drivers\.
5. Registry verification. Run regedit and search for "WinAC" and "RTX". All entries should be absent.
6. STEP 7 verification. Open the PC station project in SIMATIC Manager or TIA Portal and recompile. No missing-slot errors should be reported.

11. Troubleshooting Matrix

12. Reinstalling WinAC RTX if Required

If the engineer decides to restore the SoftPLC environment, the install media must be matched to the host operating system. WinAC RTX versions are tied to specific Windows releases:

Always consult the Siemens Industry Online Support portal for the latest compatibility matrix and the corresponding installation manual for the specific version. The WinAC RTX 3.1 Overview PDF is the canonical reference for the V3.1 line.

13. FAQ