= TeX format file
{c}
A \b[TeX format file] stores initialized internal structures for a <TeX format>, usually under a `.fmt` filename. Loading it reconstructs prepared definitions and related state more quickly than rereading the initialization input. Creating it uses the initialization facility and the `\dump` command.<TeX by Topic by Victor Eijkhout>[§33.1.2, pp.257–258: compact internal dump, load and initialization]{ref}
This is an example of <serialization>. Suppose an initialization input defines `\def\banner{First}` and its state is saved. Changing the original input to define `Second` does not by itself replace the already saved state. The format must be regenerated, or the loaded definition explicitly changed, for subsequent processing to use that new initialization.
A loaded <TeX format file> initializes future document processing. The document can then add further <TeX macros>, change parameters and request <mathematical typesetting>. The relevant implementation must be able to read the saved representation; a `.fmt` suffix alone does not establish compatibility between different implementations.
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