# Initialization: Overview

When developing TWL or NITRO applications using the TWL-SDK, always call `OS_Init` as soon as `NitroMain` is entered. The functions called internally by `OS_Init` are required for proper behavior and cannot be called in any other order.
(In the sample demo `os/cplusplus-1`, implemented in C++, the `OS_Init` function is called before `NitroMain` because memory management needs to be initialized.)

The functions called inside `OS_Init` differ depending on whether the system is operating in NITRO or TWL mode. For details, see the `OS_Init` function.

## See Also

`OS_Init
` OS Function List

## Revision History

2009/06/03 Initial version.

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