> For the complete documentation index, see [llms.txt](https://xlswriter-docs.viest.me/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://xlswriter-docs.viest.me/english/memory.md).

# 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`.