What Is Blob Data? Definition, Examples & FAQ (2026)

What Is Blob Data? (Direct Definition)

Blob data (Binary Large Object) is a data type that stores large, unstructured binary data - such as images, video, audio, or documents - as a single raw byte sequence in a database or storage system.

BLOB stands for Binary Large Object, and it describes a way of holding raw binary data inside a database or file system when that data doesn't fit neatly into standard column types like integers or text strings. The key characteristic of blob data is that it has no predefined internal structure. The system storing it treats the entire chunk as a single, opaque sequence of bytes; it doesn't inspect or interpret what's inside.

If you've ever stored a JPEG, an MP3, a PDF, a video file, or a ZIP archive in a database, you've worked with blob data. The term itself entered mainstream technical usage in the late 1980s, coined specifically to describe data too large or too unstructured for conventional column types in relational databases.

In web browsers, the concept extends to the MDN Web API Blob object, which represents immutable raw data with two defining properties: a size measured in bytes and a MIME type. This browser-side Blob object can be read as text or binary and is separate from, but conceptually identical to, the database BLOB type.

For a broader reference on related Bluesky concepts and terms, the BluePilot FAQ covers platform-specific definitions. If you're coming to this topic from a social media angle, the guide on what is Bluesky Social provides useful background on the platform where blob data plays a significant technical role. Cloudflare's explainer on blob storage and DBVisualizer's BLOB data type guide are both solid starting points for deeper reading.

How Blob Data Works: Databases, Cloud Storage & Social Platforms

SQL Databases

In relational databases, BLOB is a first-class column data type. MySQL is the clearest example, offering four size-tiered sub-types: TINYBLOB (up to 255 bytes), BLOB (up to 65KB), MEDIUMBLOB (up to 16MB), and LONGBLOB (up to 4GB). PostgreSQL handles binary data through its bytea type or via large object storage, achieving equivalent functionality. You can read a full breakdown of these variants in DBVisualizer's BLOB data type guide.

It's important to distinguish BLOB from TEXT or VARCHAR. A TEXT column stores character data encoded in a character set like UTF-8, which means the database understands the content as readable strings and can sort or compare it. A BLOB column stores raw bytes with no encoding assumption at all. Inserting a JPEG into a TEXT column will corrupt the data because the encoding conversion will mangle the bytes. Use TEXT for human-readable strings; use BLOB for anything binary. This distinction is well documented on Stack Overflow and holds across virtually every SQL engine.

One architectural consideration: storing large blobs directly in a relational database table can hurt query performance, since the binary payload sits alongside the indexed metadata the database is trying to scan. A common pattern is to store only a reference URL or storage key in the database column, while the actual binary object lives in dedicated external storage.

NoSQL and Cloud Object Storage

In NoSQL databases like MongoDB, binary data is stored using the BSON BinData type. It's functionally equivalent to a SQL BLOB, just named differently because of MongoDB's document-oriented model.

Cloud blob storage takes the concept further. Services like Azure Blob Storage, Cloudflare R2, and AWS S3 are built around an object storage architecture where every file, regardless of type, is stored as an unstructured binary object inside a flat container or bucket. There's no folder hierarchy by default. Each object is addressed by a unique key, and you retrieve it via that key or a URL. Cloudflare's cloud storage guide explains this model clearly. It's optimised for large, static, or infrequently modified files: media libraries, backups, data archives, and similar workloads.

Blobs in the Browser

The MDN Web API Blob brings blob handling into the browser environment. You can create a Blob programmatically with new Blob([data], { type: 'image/png' }) and then generate a temporary object URL using URL.createObjectURL(blob). This lets you offer file downloads or render image previews entirely in the browser without a server round-trip, which is a pattern you'll encounter frequently in file upload UIs and media editors.

Git Blobs

Git uses blob objects internally to store file content. Every tracked version of every file in a repository is saved as a blob: a compressed binary snapshot identified by its SHA-1 hash, completely separate from tree objects (which hold directory structure) and commit objects (which hold history). This separation is what allows Git to deduplicate file content efficiently across commits. A Reddit explanation in r/git covers this well for anyone new to the concept.

Blob Data on Bluesky

This is where blob data becomes directly relevant to social media users. Bluesky, which is built on the AT Protocol (you can read more in the guide to what is the Bluesky app and the overview of who owns Bluesky), stores all media as blob references within each user's repository.

When you upload a profile picture, a post image, or a video to Bluesky, the AT Protocol sends the binary data to your Personal Data Server (PDS). The PDS assigns the blob a Content Identifier (CID), which is a cryptographic hash of the content itself, and then embeds a lightweight blob reference in the corresponding Lexicon record. The binary data and the social post metadata are stored separately, which is a core part of how Bluesky's decentralised feeds work.

Bluesky enforces size limits and MIME type validation at the PDS level before accepting a blob, which is part of how the platform maintains content integrity. You can learn more about the safety implications of this in the Is Bluesky Safe guide. This architecture also means that tools like those covered in the Bluesky video downloader guide retrieve media by resolving blob references directly. It's one of the technical features that distinguishes Bluesky from platforms like Threads, where media handling is opaque and centralised.

Directories like blueskydirectory.com catalogue Bluesky tools and features at a useful surface level, but they don't cover the AT Protocol blob mechanics described here.

Blob Data: Frequently Asked Questions

What is a blob?

A blob is a Binary Large Object: any chunk of raw binary data (image, video, audio, document) stored as a single entity without an enforced internal structure. The system holding it treats the bytes as opaque. The term appears across databases, web browsers, cloud storage, and version control systems, always carrying the same core meaning.

What is blob storage?

Blob storage is a cloud object storage model where each file is stored as an unstructured binary object, accessed via a unique key or URL rather than a file path. Services like Azure Blob Storage, AWS S3, and Cloudflare R2 use this architecture. It's well-suited to media assets, backups, and any large files that don't need frequent in-place modification.

What's the difference between blob storage and block storage?

Blob (object) storage accesses data via HTTP using unique keys and is optimised for large file retrieval at scale. Block storage divides data into fixed-size chunks with low-latency I/O, making it the right choice for databases and OS volumes. The access pattern is the defining difference.

Is BLOB the same as TEXT in SQL?

No. A TEXT column stores charset-encoded, collation-aware character data. A BLOB column stores raw bytes with no encoding assumption. Inserting binary data into a TEXT column corrupts it. The Stack Overflow thread on BLOBs in DBMS contexts explains this in detail.

What is a Blob in JavaScript?

The browser Blob Web API object represents immutable raw binary data with a size (in bytes) and a type (MIME string). You create one with new Blob([data], { type: 'image/png' }) and can generate a temporary URL with URL.createObjectURL(blob) for in-browser previews or downloads.

How does Bluesky use blobs?

Every profile avatar, banner, post image, and video on Bluesky is stored as a blob reference in the AT Protocol user repository. The binary data lives on the user's PDS, identified by a CID hash, while the social record holds only the reference. This decoupled design makes Bluesky's media handling both verifiable and portable. Understanding this architecture is useful context if you're exploring what a Bluesky handle is, how Bluesky lists work, or how BluePilot interacts with Bluesky's data layer.

If you're building a presence on Bluesky and want to grow a relevant, organic audience on the platform, BluePilot's Bluesky marketing guide is a useful next read. BluePilot handles the growth mechanics so you can focus on the content side. Sign up for free to get started.