added explanatory material about servicing stack updates

windows/deployment/TOC.md

@@ -213,6 +213,7 @@
 
 ## [Update Windows 10](update/index.md)
 ### [Quick guide to Windows as a service](update/waas-quick-start.md)
+#### [Servicing stack updates](update/servicing-stack-updates.md)
 ### [Overview of Windows as a service](update/waas-overview.md)
 ### [Prepare servicing strategy for Windows 10 updates](update/waas-servicing-strategy-windows-10-updates.md)
 ### [Build deployment rings for Windows 10 updates](update/waas-deployment-rings-windows-10-updates.md)

windows/deployment/update/servicing-stack-updates.md

@@ -0,0 +1,41 @@
+---
+title: Servicing stack updates (Windows 10)
+description: Servicing stack updates improve the code that installs the other updates.
+ms.prod: w10
+ms.mktglfcycl: manage
+ms.sitesec: library
+author: Jaimeo
+ms.localizationpriority: high
+ms.author: jaimeo
+ms.date:05/27/2018
+---
+
+# Servicing stack updates
+
+
+**Applies to**
+
+- Windows 10
+- Windows 10 Mobile
+- Windows 10 IoT Mobile
+
+## What is a servicing stack update?
+The "servicing stack" is the code that installs other operating system updates. Additionally, it contains the "component-based servicing stack" (CBS), which is a key underlying component for several elements of Windows deployment, such as DISM, SFC, changing Windows features or roles, and repairing components. The CBS is a small component that typically does not have updates released every month.
+
+## Why should servicing stack updates be installed and kept up to date?
+  
+Having the latest servicing stack update is a prerequisite to reliably installing the latest quality updates and feature updates.  
+
+## When are they released?
+
+Currently, the servicing stack update releases are aligned with the monthly quality update release date, though sometimes they are released on a separate date if required.
+
+## Is there any special guidance?
+
+Typically, the improvements are reliability, security, and performance improvements that do not require any specific special guidance. If there is any significant impact is will be present in the release notes.
+
+## Installation notes
+
+•	Servicing stack updates contain the full servicing stack; as a result, typically administrators only need to install the latest servicing stack update for the operating system.
+•	Installing servicing stack update does not require restarting the device, so installation should not be disruptive.  
+•	Servicing stack update releases are specific to the operating system version (build number), much like quality updates.

windows/deployment/update/waas-quick-start.md

@@ -7,7 +7,7 @@ ms.sitesec: library
 author: Jaimeo
 ms.localizationpriority: high
 ms.author: jaimeo
-ms.date: 02/09/2018
+ms.date:05/27/2018
 ---
 
 # Quick guide to Windows as a service
@@ -25,7 +25,7 @@ Windows as a service is a new concept, introduced with the release of Windows 10
 
 Some new terms have been introduced as part of Windows as a service, so you should know what these terms mean.
 - **Feature updates** will be released twice per year, around March and September.  As the name suggests, these will add new features to Windows 10, delivered in bite-sized chunks compared to the previous practice of Windows releases every 3-5 years.
-- **Quality updates** are released monthly, delivering both security and non-security fixes.  These are cumulative, so installing the latest quality update is sufficient to get all the available fixes for a specific Windows 10 feature update.
+- **Quality updates** are released monthly, delivering both security and non-security fixes. Typically released the second Tuesday of each month (though they can be released at any time), these include security updates, critical updates, servicing stack updates, and driver updates. The "servicing stack" is the code that installs other updates, so they are especially important to keep current. For more information, see [Servicing stack updates](servicing-stack-updates.md)  Quality updates are cumulative, so installing the latest quality update is sufficient to get all the available fixes for a specific Windows 10 feature update.
 - **Insider Preview** builds are made available during the development of the features that will be shipped in the next feature update, enabling organizations to validate new features as well as compatibility with existing apps and infrastructure, providing feedback to Microsoft on any issues encountered.
 - **Servicing channels** allow organizations to choose when to deploy new features. 
     - The **Semi-Annual Channel** receives feature updates twice per year.