Below is a list of all the sweet improvements made to the .NET Framework 3.5 Service Pack 1 since the .NET Framework 3.5 was initially released!
"NGen infrastructure rewrite: the new infrastructure uses less memory, produces less fragmented NGen images with much better locality, and does so in dramatically less time. What this means to you: Installing or servicing an NGen image is much faster, and cold startup time of your NGen’ed code is better.
Framework Startup Performance Improvements: The framework is now better optimized for startup. We’ve tweaked the framework to consider more scenarios for startup, and now layout both code & data in the framework’s NGen images more optimally. What this means to you: Even your JIT code starts faster!
Better OS citizenship: We’ve modified NGen to produce images that are ASLR capable, in an effort to decrease potential security attack surface area. We’ve also started generating stacks that are always walkable using EBP-chaining for x86. What this means to you: Stack traces are more consistent, and NGen images aren’t as easily used to attack the system.
Better 32-bit code quality: The x86 JIT has dramatically improved inlining heuristics that result in generally better code quality, and, in particular, much lower “cost of abstraction”. If you want to author a data type that only manipulates a single integer, you can wrap the thing in a struct, and expect similar performance to code that explicitly uses an integer. There have also been some improvements to the ‘assertion propagation’ portion of the JIT, which means better null/range check elimination, as well as better constant propagation, and slight better ‘smarts’ in the JIT optimizer, overall. What this means to you: Your managed code should run slightly faster (and sometimes dramatically faster!). Note to 64 bit junkies: We’re working on getting x64 there, too. The work just wasn’t quite there in time." ( JIT, NGen, and other Managed Code Generation Stuff )