The Execution Counts window shows a list of source locations and the number of times those source locations have been executed. This window is only available for targets that support the collection of jump trace information.
The count value displayed is the number of times the first instruction of the source code location has been executed. The source locations displayed are target dependent: they could represent each statement of the program or each jump target of the program. If however the debugger is in intermixed or disassembly mode then the count values will be displayed on a per instruction basis.
The execution counts window is updated each time your program stops and the window is visible so if you have this window displayed then single stepping may be slower than usual.