S3 – Simple Storage Service – An object storage access protocol devised by AWS which has become a standard across the storage industry. It currently stores about 280 trillion objects. An object is a set of data with an identity. It is not a file with a filesystem folder-based address nor is it a set of storage drive blocks with a location address relative to the drive’s start address, as in a SAN with its LUNs (virtual drives).

S3 objects are stored in virtual repositories called buckets which can store any amount of data. They are not fixed in size. Buckets are stored in regions of the AWS infrastructure, meaning they have a two-part address: region name followed by a user-assigned key. 

S3 buckets have access controls which define which users can access them and what can be done to the bucket’s contents. There are eight different classes of S3 storage: Standard,  Standard-Infrequent Access (Standard-IA), One Zone-Infrequent Access (One Zone-IA), Intelligent-Tiering,  S3 on Outposts,  Glacier Instant Retrieval,  Glacier Flexible Retrieval, and Glacier Deep Archive.

S3 objects can be between 1 byte and 5TB in size, with 5TB being the maximum S3 object upload size. Data objects larger than 5TB are split into smaller chunks and sent to S3 in a multi-part upload operation.

Since S3 buckets can store anything, they can store files. An object can have a user-assigned key prefix that represents its access path. For example, Myfile.txt could have a BucketName/Project/Document/Myfile.txt prefix.

There is a flat S3 address space, unlike a hierarchical file:folder system, but S3 does use the concept of a folder to group and display objects within a bucket. The “/“ character in an object’s key prefix separates folder names. So, in the key prefix BucketName/Project/Document/Myfile.txt prefix, there is a folder, Project, and sub-folder, Document, with both classed as folders.

All this means that data stored in an S3 bucket can look as if it is stored and addressed in a file:folder system but it is not. An object’s key is its full path, in this case BucketName/Project/Document/Myfile.txt. AWS uses the / character to delineate virtual Project and Document folders but they are not used as part of the object’s location process, only for grouping and display purposes.

The S3 folder construct is just used to group objects together but not to address them in a hierarchical fashion. S3 buckets are effectively bottomless.