GAC

//=== GAC (Global Assembly Cache)

[Q] Where is GAC?
[try]

• for .net 1.x, .net 2.x, .net 3.x :
  %windir%\assembly\...   --> e.g. C:\Windows\assembly
• .net4.0 :
  %windir%\Microsoft.NET\assembly\... -> e.g. C:\Windows\Microsoft.NET\assembly\...

//=== .NET Framework
[Q] How to know which .NET Framework versions are installed?
[try]

• check registry 
  HKEY_LOCAL_MACHINE\Software\Microsoft\.NETFramework
• check %windir%\Microsoft.NET\Framework directory will have the directories
  v1.x , v2.x, ...

 //===

[Q] Where is gacutil.exe ?

[try]

install Windows SDK suitable for the targeting version of Windows and .net framework

e.g. for Win7 + .net3.5sp1 ,

download iso file from

http://www.microsoft.com/downloads/en/details.aspx?FamilyID=C17BA869-9671-4330-A63E-1FD44E0E2505

 //=== Microsoft Windows SDK for Windows 7 and .NET Framework 3.5 SP1 (ISO)

File Name: GRMSDK_EN_DVD.iso

Chip: X86
CRC#: 0xCA4FE79D
SHA1: 0x8695F5E6810D84153181695DA78850988A923F4E
================================================
File Name: GRMSDKX_EN_DVD.iso
Chip: AMD64
CRC#: 0xB417A4F7
SHA1: 0x3393C98B8468CB3505557854922707510F8B65E1
================================================
File Name: GRMSDKIAI_EN_DVD.iso
Chip: Itanium
CRC#: 0x5E0E4BEA
SHA1: 0xAE454215585A044EBE593E9F71FF1A4BC03D56A8

  

[ref]

http://en.wikipedia.org/wiki/Global_Assembly_Cache

http://www.pcreview.co.uk/forums/which-net-framework-version-installed-t1346870.html

http://stackoverflow.com/questions/3397479/where-is-gacutil-exe