||How to Boost XP Performance|
|Subject:||Reducing Color Depth can Impede Performance|
Reducing the color depth from 32 bits (24 bits padded to 32) down to 16 bits can save memory, which in turn can significantly improve performance when you're using a system which shares memory between the graphics system and the CPU (e.g., Intel i810 family).
However, if you're not short on RAM, using 16-bit graphics can dramatically slow down graphics operations -- especially when the CPU is doing the work -- depending on what operations you are performing.
At 32 bits per pixel, the CPU can write a full 32-bit word to change the color of one pixel. When using 16 bits per pixel, there are two pixels in every 32-bit word. To change the color of one pixel, the CPU has to read the word from memory, perform an AND to preserve the unaffected pixel's value, perform an OR to insert the affected pixel's value, and then write the word pack to memory -- 4 operations instead of 1 (and that's when you're changing the low-order pixel; add a 16-bit left shift when you're changing the high-order pixel).