MOBI vs PDB — Differences, File Size & When to Use Each

MOBI vs PDB

A detailed comparison of Mobipocket eBook and PalmDOC eBook — file size, quality, compatibility, and which format to choose for your workflow.

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MOBI

Mobipocket eBook

eBooks

MOBI is the Mobipocket eBook format historically used by Amazon Kindle devices. While Amazon has moved to newer formats, MOBI remains relevant for older Kindles and legacy eBook libraries.

About MOBI files

PDB

PalmDOC eBook

eBooks

PDB (Palm Database) is a generic database format from the Palm OS era that was widely used for ebooks on Palm handheld devices. PalmDOC and Mobipocket both use PDB as their underlying container for storing text-based ebook content.

About PDB files

Strengths Comparison

MOBI Strengths

Universal Kindle support on every device ever released.
Very small file sizes for text-heavy books.
Mature tooling via Calibre and Amazon's KindleGen.
Simple container structure — easy to parse.

PDB Strengths

Compact record-based structure for low-RAM devices.
Basis of PalmDOC, Mobipocket, eReader, and Kindle AZW formats.
Well-documented.
Simple to parse — stable for 30 years.

Limitations

MOBI Limitations

Deprecated by Amazon for new uploads since 2022.
Poor support for rich typography (drop caps, ligatures, fixed layout).
No embedded fonts in the base format.
Proprietary container discouraged use outside Kindle.
Effectively a legacy format — new books go to AZW3/EPUB.

PDB Limitations

Ecosystem collapsed with Palm's hardware business.
Name collides with biochemistry's Protein Data Bank PDB.
Modern ebook tooling prefers EPUB, AZW3, or direct formats.
Very little new content written as PDB in 2026.

Technical Specifications

Specification	MOBI	PDB
MIME type	application/x-mobipocket-ebook	—
Extension	.mobi, .prc (PalmDOC variant)	.pdb
Container	Palm Database (PDB)	—
Markup	Compressed HTML subset	—
Successor	.azw, .azw3 (Kindle-specific)	—
MIME types	—	application/vnd.palm (Palm), chemical/x-pdb (biochemistry)
Palm structure	—	Header + record list + record data
Related formats	—	PalmDOC, Mobipocket MOBI, AZW
Namespace clash	—	Biochemistry Protein Data Bank is a different format entirely

Typical File Sizes

MOBI

Text-only novel 200 KB - 1 MB
Illustrated book 2-10 MB

PDB

PalmDOC ebook (text novel) 200 KB - 2 MB
PalmOS app data store 10 KB - 500 KB
Protein Data Bank file (biochemistry) 50 KB - 5 MB

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Frequently Asked Questions

MOBI (Mobipocket eBook) is an ebook format designed for reading long-form text on dedicated e-readers, tablets, and ebook apps. It is part of the ebooks family and typically supports reflowable text, embedded images, chapter navigation, cover art, and metadata (title, author, ISBN) in a portable package.

MOBI (Mobipocket eBook) is an ebook formato designed para reading long-form text on dedicated e-readers, tablets, e ebook apps. It is part of the ebooks family e tipicamente suporta reflowable text, embedded images, chapter navigation, cover art, e metadata (title, author, ISBN) em um portable package.

Dedicated e-readers — Kindle, Kobo, Nook, Pocketbook — support the most common ebook formats. On phones, Apple Books, Google Play Books, Moon+ Reader and KOReader all handle MOBI. For desktop reading, Calibre is the universal ebook viewer and library manager. Convert to EPUB or PDF for maximum compatibility.

Dedicated e-readers — Kindle, Kobo, Nook, Pocketbook — support the most common ebook formatoos. On phones, Apple Books, Google reproduzir Books, Moon+ Reader e KOReader all handle MOBI. para desktop reading, Calibre is the universal ebook viewer e library manager. converter to EPUB ou PDF para máximo compatibilidade.

Upload your MOBI to KaijuConverter and pick EPUB, MOBI, PDF, AZW3, or similar targets. Our Calibre-powered pipeline preserves chapter structure, embedded images, cover art, and metadata. Conversion takes seconds for typical novels; long technical books with many images may take a little longer.

EPUB is the open ebook standard — it plays on every e-reader except older Kindles and in every major ebook app. PDF is better for fixed-layout content (textbooks, coffee-table books) and printing. Pick EPUB when the ebook is reflowable text, PDF when the layout matters more than the reading experience.