cycles and after the release of the software. Unlike event logging, software tracing usually does not have the concept of a "class" of event or an "event code". Other reasons why event-logging solutions based on event codes are inappropriate for software tracing include: Because software tracing is low-level, there are often many more types of messages that would need to be defined, many of which would only be used at one place in the code. The event-code paradigm introduces significant development overhead for these "one-shot" messages. The types of messages that are logged are often less stable through the development cycle than for event logging. Because the tracing output is intended to be consumed by the developer, the messages don't need to be localized. Keeping tracing messages separate from other resources that need to be localized (such as event messages) is therefore important. There are messages that should never be seen. Tracing messages should be kept in the code, because they can add to the readability of the code. This is not always possible or feasible with event-logging solutions. Another important consideration for software tracing is performance. Because software tracing is low-level, the possible volume of trace messages is much higher. To address performance concerns, it often must be possible to turn off software tracing, either at compile-time or run-time. Other special concerns: In proprietary software, tracing data may include sensitive information about the product's source code. If tracing is enabled or disabled at run-time, many methods of tracing require the inclusion of a significant amount of additional data in the binary, which can indirectly hurt performance even when tracing is disabled. If tracing is enabled or disabled at compile-time, getting trace data for a problem on a customer machine depends on the customer being willing and able to install a special, tracing-enabled version of the software and then duplicating the problem. Many uses of tracing have very stringent robustness requirements. This is both in the robustness of the trace output but also in that the use-case being traced should not be disrupted. In operating systems, tracing is sometimes useful in situations (such as booting) where some of the technologies used to provide event logging may not be available. in embedded software, tracing requires special techniques. Techniques Software tracing: Tracing macros Output to debugger Aspect-oriented programming and related instrumentation techniques Windows software trace preprocessor (aka WPP) FreeBSD and SmartOS tracing