# Memory model

xlswriter offers two memory strategies for writing files:

* **Normal mode** — the entire workbook is held in memory; fastest but proportional to data size.
* [**Fixed memory mode**](/english/memory/fixed-memory.md) — rows are flushed to disk as they are written, keeping peak memory under \~1 MB regardless of file size. Recommended for exporting millions of rows.

Pick fixed memory mode whenever the dataset may not fit comfortably in PHP's `memory_limit`.


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