Deferred Symbol Loading
By default, symbol information is not actually loaded when the target modules are loaded. Instead, symbols are loaded by the debugger as they are needed. This is called deferred symbol loading or lazy symbol loading. When this option is enabled, the debugger loads symbols whenever it encounters an unrecognized symbol.
When deferred symbol loading is disabled, process startup can be much slower, because all symbols are read whenever a module is loaded.
In WinDbg, the deferred symbol loading behavior can be modified for symbols that have no module prefix by using the Resolve Unqualified Symbols option on the Debug menu.
You can override deferred symbol loading by using the ld (Load Symbols) command or the .reload (Reload Module) command with the /f option. These force the specified symbols to be loaded immediately, although the loading of other symbols is deferred. If the symbol path is changed, symbols are not automatically reloaded.
By default, deferred symbol loading is enabled. In CDB and KD, the -scommand-line option will turn this option off. It can also be turned off in CDB by using the LazyLoad variable in the tools.ini file. Once the debugger is running, this option can be turned on or off by using .symopt+0x4 or .symopt-0x4, respectively.