Every Windows has had significant functionality additions. The closest to a "weak" service pack was Windows 7.
Service Pack 1
It contains post-RTM security fixes and hot-fixes, compatibility updates, optional .NET Framework support, enabling technologies for new devices such as Tablet PCs, and a new Windows Messenger 4.7 version. The most notable new features were USB 2.0 support and a Set Program Access and Defaults utility that aimed at hiding various middleware products. Users can control the default application for activities such as web browsing and instant messaging, as well as hide access to some of Microsoft's bundled programs. This utility was first brought into the older Windows 2000 operating system with its Service Pack 3. This Service Pack supported SATA and hard drives that were larger than 137 GB (48-bit LBA support) by default. The Microsoft Java Virtual Machine, which was not in the RTM version, appeared in this Service Pack. It also removed the Energy Star logo from the ScreenSaver tab of the Display properties, leaving a very noticeable blank space next to the link to enter the Power Management control panel. Support for IPv6 was also introduced in this Service Pack.
Service Pack 2
Windows Security Center was added in Service Pack 2. Service Pack 2 (SP2) was released on August 25, 2004, with an emphasis on security. Unlike the previous service pack, SP2 added new functionality to Windows XP, such as WPA encryption compatibility and improved Wi-Fi support (with a wizard utility), a pop-up ad blocker for Internet Explorer 6, and partial Bluetooth support. The new welcome screen during the kernel boot removes the subtitles "Professional", "Home Edition" and "Embedded" since Microsoft introduced new Windows XP editions prior to the release of SP2. The green loading bar in Home Edition and the yellow one in Embedded were replaced with the blue bar, seen in Professional and other versions of Windows XP, making the boot-screen of operating systems resemble each other. Colors in other areas, such as Control Panel and the Help and Support tool, remained as before.
Service Pack 2 also added new security enhancements (codenamed "Springboard"), which included a major revision to the included firewall that was renamed to Windows Firewall and became enabled by default, Data Execution Prevention, which can be weakly emulated,[clarification needed] gains hardware support in the NX bit that can stop some forms of buffer overflow attacks. Also raw socket support is removed (which supposedly limits the damage done by zombie machines). Additionally, security-related improvements were made to e-mail and web browsing. Windows XP Service Pack 2 includes the Windows Security Center, which provides a general overview of security on the system, including the state of antivirus software, Windows Update, and the new Windows Firewall. Third-party anti-virus and firewall applications can interface with the new Security Center.
Service Pack 3
Windows XP Service Pack 3 (SP3) was released to manufacturing on April 21, 2008, and to the public via both the Microsoft Download Center and Windows Update on May 6, 2008.
A feature set overview which details new features available separately as stand-alone updates to Windows XP, as well as backported features from Windows Vista, has been posted by Microsoft. A total of 1,174 fixes have been included in SP3. Service Pack 3 can be installed on systems with Internet Explorer versions 6, 7, or 8. Internet Explorer 7 and 8 are not included as part of SP3.
New features in Service Pack 3
NX APIs for application developers to enable Data Execution Prevention for their code, independent of system-wide compatibility enforcement settings 
Turns black hole router detection on by default
Support for SHA-2 signatures in X.509 certificates 
Network Access Protection client
Group Policy support for IEEE 802.1X authentication for wired network adapters.
Credential Security Support Provider
Descriptive Security options in Group Policy/Local Security Policy user interface
An updated version of the Microsoft Enhanced Cryptographic Provider Module (RSAENH) that is FIPS 140-2 certified (SHA-256, SHA-384 and SHA-512 algorithms)
Installing without requiring a product key during setup for retail and OEM versions
Service Pack 1
Windows Vista Service Pack 1 (SP1) was released on February 4, 2008, alongside Windows Server 2008 to OEM partners, after a five-month beta test period. The synchronized release date of the two operating systems reflected the merging of the workstation and server kernels back into a single code base for the first time since Windows 2000. MSDN subscribers were able to download SP1 on February 15, 2008.
A whitepaper published by Microsoft near the end of August 2007 outlined the scope and intent of the service pack, identifying three major areas of improvement: reliability and performance, administration experience, and support for newer hardware and standards.
Service Pack 1 introduced support for some new hardware and software standards, notably the exFAT file system, 802.11n wireless networking, IPv6 over VPN connections, and the Secure Socket Tunneling Protocol.
Booting a system using Extensible Firmware Interface on x64 systems was also introduced; this feature had originally been slated for the initial release of Vista but was delayed due to a lack of compatible hardware at the time. Booting from a GUID Partition Table–based hard drive greater than 2.19 TB is supported (x64 only).
Two areas have seen changes in SP1 that have come as the result of concerns from software vendors. One of these is desktop search; users will be able to change the default desktop search program to one provided by a third party instead of the Microsoft desktop search program that comes with Windows Vista, and desktop search programs will be able to seamlessly tie in their services into the operating system. These changes come in part due to complaints from Google, whose Google Desktop Search application was hindered by the presence of Vista's built-in desktop search. In June 2007, Google claimed that the changes being introduced for SP1 "are a step in the right direction, but they should be improved further to give consumers greater access to alternate desktop search providers". The other area of note is a set of new security APIs being introduced for the benefit of antivirus software that currently relies on the unsupported practice of patching the kernel (see Kernel Patch Protection).
An update to DirectX 10, named DirectX 10.1, marked mandatory several features that were previously optional in Direct3D 10 hardware. Graphics cards will be required to support DirectX 10.1. SP1 includes a kernel (6001.18000) that matches the version shipped with Windows Server 2008.
The Group Policy Management Console (GPMC) was replaced by the Group Policy Object Editor. An updated downloadable version of the Group Policy Management Console was released soon after the service pack.
SP1 enables support for hotpatching, a reboot-reduction servicing technology designed to maximize uptime. It works by allowing Windows components to be updated (or "patched") while they are still in use by a running process. Hotpatch-enabled update packages are installed via the same methods as traditional update packages, and will not trigger a system reboot.
Service Pack 2
Service Pack 2 for Windows Vista was released to manufacturing on April 28, 2009, and released to Microsoft Download Center and Windows Update on May 26, 2009. In addition to a number of security and other fixes, a number of new features have been added. However, it did not include Internet Explorer 8:
Windows Vista Service Pack 2 is build 6002.18005.090410-1830.
Windows Search 4.0 (currently available for SP1 systems as a standalone update)
Feature Pack for Wireless adds support for Bluetooth 2.1
Windows Feature Pack for Storage enables the data recording onto Blu-ray media
Windows Connect Now (WCN) to simplify Wi-Fi configuration
Improved support for resuming with active Wi-Fi connections
Improved support for eSATA drives
The limit of 10 half open, outgoing TCP connections was removed
Enables the exFAT file system to support UTC timestamps, which allows correct file synchronisation across time zones
Support for ICCD/CCID smart cards
Support for VIA 64-bit CPUs
Improved performance and responsiveness with the RSS feeds sidebar
Improves audio and video performance for streaming high-definition content
Improves Windows Media Center (WMC) in content protection for TV
Provides an improved power management policy that is up to 10% more efficient than the original in some[clarification needed] configurations
Windows Vista and Windows Server 2008 share a single service pack binary, reflecting the fact that their code bases were joined with the release of Server 2008. Service Pack 2 is not a cumulative update meaning that Service Pack 1 must be installed first.
The Platform Update for Windows Vista was released on October 27, 2009. It includes major new components that shipped with Windows 7, as well as updated runtime libraries. It requires Service Pack 2 of Windows Vista or Windows Server 2008 and is listed on Windows Update as a Recommended download.
The Platform Update allows application developers to target both Windows Vista and Windows 7. It consists of the following components:
Windows Graphics runtime: Direct2D, DirectWrite, Direct3D 11, DXGI 1.1, and WARP;
Updates to Windows Imaging Component;
Updates to XPS Print API, XPS Document API and XPS Rasterization Service;
Windows Automation API (updates to MSAA and UI Automation);
Windows Portable Devices Platform; (adds support for MTP over Bluetooth and MTP Device Services)
Windows Ribbon API;
Windows Animation Manager library.
Some updates will also be available as separate releases for both Windows XP and Windows Vista:
Windows Management Framework: Windows PowerShell 2.0, Windows Remote Management 2.0, BITS 4.0
Remote Desktop Connection 7.0 (RDP7) client
Although extensive, the Platform Update does not bring Windows Vista to the level of features and performance offered by Windows 7. For example, even though Direct3D 11 runtime will be able to run on D3D9-class hardware and WDDM drivers using "feature levels" first introduced in Direct3D 10.1, Desktop Window Manager has not been updated to use Direct3D 10.1.
In July 2011, Microsoft released Platform Update Supplement for Windows Vista and Windows Server 2008, which contains bugfixes and performance improvements.