Amazon S3 objects overview - Amazon Simple Storage Service
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Amazon S3 objects overview

Amazon S3 is an object store that uses unique key-values to store as many objects as you want. You store these objects in one or more buckets, and each object can be up to 5 TB in size. An object consists of the following:


The name that you assign to an object. You use the object key to retrieve the object. For more information, see Working with object metadata.

Version ID

Within a bucket, a key and version ID uniquely identify an object. The version ID is a string that Amazon S3 generates when you add an object to a bucket. For more information, see Using versioning in S3 buckets.


The content that you are storing.

An object value can be any sequence of bytes. Objects can range in size from zero to 5 TB. For more information, see Uploading objects.


A set of name-value pairs with which you can store information regarding the object. You can assign metadata, referred to as user-defined metadata, to your objects in Amazon S3. Amazon S3 also assigns system-metadata to these objects, which it uses for managing objects. For more information, see Working with object metadata.


Amazon S3 uses the subresource mechanism to store object-specific additional information. Because subresources are subordinates to objects, they are always associated with some other entity such as an object or a bucket. For more information, see Object subresources.

Access control information

You can control access to the objects you store in Amazon S3. Amazon S3 supports both the resource-based access control, such as an access control list (ACL) and bucket policies, and user-based access control. For more information about access control, see the following:

Your Amazon S3 resources (for example, buckets and objects) are private by default. You must explicitly grant permission for others to access these resources. For more information about sharing objects, see Sharing objects with presigned URLs.


You can use tags to categorize your stored objects, for access control, or cost allocation. For more information, see Categorizing your storage using tags.

Object subresources

Amazon S3 defines a set of subresources associated with buckets and objects. Subresources are subordinates to objects. This means that subresources don't exist on their own. They are always associated with some other entity, such as an object or a bucket.

The following table lists the subresources associated with Amazon S3 objects.

Subresource Description
acl Contains a list of grants identifying the grantees and the permissions granted. When you create an object, the acl identifies the object owner as having full control over the object. You can retrieve an object ACL or replace it with an updated list of grants. Any update to an ACL requires you to replace the existing ACL. For more information about ACLs, see Access control list (ACL) overview.