What makes a custom ROM faster?

[rstoyguy]

Originally Posted by FormerPalmOS

There are some known performance tweaks (registry edits for file system caches, disabling some unnecessary services, etc.). These tweaks can be made to a stock ROM as well. So my question is this: What about a custom ROM makes it faster than a stock ROM?

One item I can think of is increasing the amount of free program memory so that the above-referenced cache sizes can also be increased, however increasing cache sizes reaches a point of diminishing returns.

Other things I can think of - using a newer build of WM (assuming the newer build is faster), using newer drivers for certain hardware components (again assuming the newer drivers are faster).

Mostly what makes a custom rom is exactly what you have stated. Tweaks to enhance battery life, speed and other quirks. Usually by removing removing some of the "extras" and a page or two of RGU registry tweaks will speed up the stock rom. At least all of my custom roms I build are based off the stock release. IMO the SYS by itself will not make a device go that much faster, Usually a new SYS is void of all the carriers "additions" and that is what makes it seem to run faster. The craze for a higher numbered sys...I'm just not gonna follow that crowd myself.