In SQL Server 2012, a new feature was added called Columnstore Indexes that resulted in huge query performance improvements.  In SQL Server 2014, there have been two major improvements on this feature:

Clustered: They have enhanced the columnstore to be a pure columnar store, so indexing is no longer required.  The In-Memory ColumnStore for data warehousing is implemented as a clustered columnstore index (or CCI) on a table.  The data in a CCI is grouped and stored for every column in the table.  Unlike the non-clustered columnstore index, the CCI is the data – there is no other underlying data structure

Updatable: You are able to insert, update, and delete data in an existing ColumnStore.  Note that a columnstore index is impossible to update “in-place” due to its highly compressed structure, so “deltastores” are used.  The same solution was done for v2 of PDW

Note you will still be able to create a non-clustered columnstore index which is not updatable.  A table with a clustered columnstore index cannot have any type of nonclustered index.

More info:

CREATE COLUMNSTORE INDEX (Transact-SQL)

SQL SERVER 2014 – Columnstore Index Enhancement – Part 1

Clustered Columnstore Indexes – part 1 (“Intro”)

Updatable columnstore index, sp_spaceused and sys.partitions

SQL SERVER CLUSTERED COLUMNSTORE INDEXES AT TECHED 2013

Video What’s New for Columnstore Indexes and Batch Mode Processing

Enhancements to SQL Server Column Stores

What’s New for Columnstore Indexes in SQL Server 2014

ColumnStore Archival Compression–SQL Server 2014

New Enhanced Column Store Index in SQL Server 2014 – Part 1