Windows Server 2008 R2
Windows Server 2008 R2 is a server operating system produced by Microsoft. It was released to manufacturing on July 22, 2009 and launched on October 22, 2009. According to the Windows Server Team blog, the retail availability was September 14, 2009. It is built on Windows NT 6.1, the same core operating system used with the end-user oriented Windows 7. It is the first 64-bit-only operating system release from Microsoft. Windows Server 2008 R2 is an update of Windows Server 2008.
There are seven editions: Foundation, Standard, Enterprise, Datacenter, Web, HPC Server and Itanium.
On January 7, 2009, a beta release of Windows Server 2008 R2 was made available to subscribers of Microsoft's TechNet and MSDN programs, as well as those participating in the Microsoft Connect program for Windows 7. Two days later, the beta was released to the public via the Microsoft Download Center.
On April 30, 2009, the release candidate was made available to subscribers of Microsoft's TechNet and MSDN. On May 5, 2009, the release candidate was made available to the general public via the Microsoft download center.
According to Windows Server Division WebLog, the following are the dates of the year 2009 when Microsoft Windows Server 2008 R2 has been made available to various distribution channels:
- OEMs received Windows Server 2008 R2 RTM in English and all Language Packs on July 29. The remaining languages were available around August 11.
- ISV (Independent software vendor) and IHV (Independent hardware vendor) partners have been able to download Windows Server 2008 R2 RTM from MSDN starting on August 14.
- IT Professionals with TechNet Subscriptions are able to download Windows Server 2008 R2 RTM in English, French, German, Italian, and Spanish on August 14 and all remaining languages beginning August 21.
- Developers with MSDN Subscriptions have been allowed to download Windows Server 2008 R2 RTM in English, French, German, Italian, and Spanish on August 14 and all remaining languages starting August 21.
- Microsoft Partner Program Gold/Certified Members were able to download Windows Server 2008 R2 RTM through the Microsoft Partner Program (MPP) Portal on August 19.
- Volume License (VL) customer with an existing Software Assurance (SA) license were able to download Windows Server 2008 R2 RTM on August 19 via the Volume License Service Center (VLSC).
- Volume License customers without a Software Assurance (SA) license can purchase Windows Server 2008 R2 through Volume Licensing on September 1.
Microsoft has announced that Server 2008 R2 will be the last version of Windows supporting the Itanium architecture.
See also: Features new to Windows 7
A reviewer guide published by the company describes several areas of improvement in version R2. These include new virtualization capabilities (Live Migration, Cluster Shared Volumes using Failover Clustering and Hyper-V), reduced power consumption, a new set of management tools and new Active Directory capabilities such as a "recycle bin" for deleted AD objects. IIS 7.5 has been added to this release which also includes updated FTP server services. Security enhancements include the addition of DNSSEC support for DNS Server Service (note: even though DNSSEC as such is supported, only one signature algorithm is available (#5 / RSA/SHA-1). Since many zones use a different algorithm - not least the root zone - this means that in reality Windows still can't serve as a recursive resolver) and encrypted clientless authenticated VPN services through DirectAccess for clients using Windows 7. The DHCP server supports a large number of enhancements  such as MAC address-based control filtering, converting active leases into reservations or Link Layer based filters, IPv4 address exhaustion[clarification needed] at scope level[clarification needed], DHCP Name protection for non-Windows machines to prevent name squatting, better performance through aggressive lease database caching, DHCP activity logging, auto-population of certain network interface fields, a wizard for split-scope configuration, DHCP Server role migration using WSMT, support for DHCPv6 Option 15 (User Class) and Option 32 (Information Refresh Time). The DHCP server runs in the context of the Network Service account which has less privileges to reduce potential damage if compromised.
Windows Server 2008 R2 supports up to 64 physical processors  or up to 256 logical processors per system. When deployed in a file server role, new File Classification Infrastructure services allow files to be stored on designated servers in the enterprise based on business naming conventions, relevance to business processes and overall corporate policies.
Performance improvement was a major area of focus for this release; Microsoft has stated that work was done to decrease boot time, improve the efficiency of I/O operations while using less processing power, and generally improve the speed of storage devices, especially iSCSI.
Active Directory has several new features when raising the forest and domain functional levels to Windows Server 2008 R2. When raising the domain function level, two added features are Authentication Mechanism Assurance and Automatic SPN Management. When raising the forest functional level, the Active Directory recycle bin feature is available and can be enabled using the Active Directory Module for Powershell.
The final build of Service Pack 1 have been finalized and is now RTM with build number 6.1.7601.17514.101119-1850 Current official release of Service Pack 1 is slated for the first quarter of 2011.
System requirements for Windows Server 2008 R2 are as follows:
Maximum: 8 GB RAM (Foundation), 32 GB RAM (Standard), or 2 TB RAM (Enterprise, Datacenter and Itanium-Based Systems)
Super VGA (800 x 600)
Disk Space Requirements
Minimum: 32 GB or more
Computers with more than 16 GB of RAM require more disk space for paging and dump files.
DVD drive, keyboard and mouse, Internet access
Source : wikipedia