ROOT version 6.08/00 has been released on November 4, 2016.

For more information, see:

The following people have contributed to this new version:

David Abdurachmanov, CERN, CMS,
Adrian Bevan, Queen Mary University of London, ATLAS,
Attila Bagoly, GSoC,
Bertrand Bellenot, CERN/SFT,
Rene Brun, CERN/SFT,
Philippe Canal, Fermilab,
Andrew Carnes, University of Florida, CMS,
Cristina Cristescu, CERN/SFT,
Olivier Couet, CERN/SFT,
Gerri Ganis, CERN/SFT,
Paul Gessinger, CERN/SFT,
Andrei Gheata, CERN/SFT,
Luca Giommi, CERN/SFT,
Sergei Gleyzer, University of Florida, CMS
Christopher Jones, Fermilab, CMS,
Wim Lavrijsen, LBNL, PyRoot,
Sergey Linev, GSI, http,
Pere Mato, CERN/SFT,
Lorenzo Moneta, CERN/SFT,
Abhinav Moudgil, GSoC,
Axel Naumann, CERN/SFT,
Simon Pfreundschuh, GSoC, CERN/SFT,
Danilo Piparo, CERN/SFT,
Timur Pocheptsov, CERN/SFT,
Fons Rademakers, CERN/IT,
Paul Russo, Fermilab,
Enric Tejedor Saavedra, CERN/SFT,
George Troska, Dortmund Univ.,
Liza Sakellari, CERN/SFT,
Alex Saperstein, ANL,
Manuel Tobias Schiller, CERN/LHCb,
David Smith, CERN/IT,
Peter Speckmayer,
Tom Stevenson, Queen Mary University of London, ATLAS
Matevz Tadel, UCSD/CMS, Eve,
Peter van Gemmeren, ANL, ATLAS,
Xavier Valls, CERN/SFT,
Vassil Vassilev, Fermilab/CMS,
Stefan Wunsch, KIT, CMS
Omar Zapata, University of Antioquia, CERN/SFT.


Core Libraries

ROOT prepares for cxx modules. One of the first requirements is its header files to be self-contained (section “Missing Includes”). ROOT header files were cleaned up from extra includes and the missing includes were added.

This could be considered as backward incompatibility (for good however). User code may need to add extra includes, which were previously resolved indirectly by including a ROOT header. For example:

Other improvements, which may cause compilation errors in third party code:



Meta Library

Add a new mode for TClass::SetCanSplit (2) which indicates that this class and any derived class should not be split. This included a rework the mechanism checking the base classes. Instead of using InheritsFrom, which lead in some cases, including the case where the class derived from an STL collection, to spurrious autoparsing (to look at the base class of the collection!), we use a custom walk through the tree of base classes that checks their value of fCanSplit. This also has the side-effect of allowing the extension of the concept ‘base class that prevent its derived class from being split’ to any user class. This fixes ROOT-7972.


Interpreter Library


I/O Libraries

TTree Libraries

Fast Cloning

We added a cache specifically for the fast option of the TTreeCloner to significantly reduce the run-time when fast-cloning remote files to address ROOT-5078. It can be controlled from the TTreeCloner, TTree::CopyEntries or hadd interfaces. The new cache is enabled by default, to update the size of the cache or disable it from TTreeCloner use: TTreeCloner::SetCacheSize. To do the same from TTree::CopyEntries add to the option string “cachesize=SIZE”. To update the size of the cache or disable it from hadd, use the command line option -cachesize SIZE. SIZE shouyld be given in number bytes and can be expressed in ‘human readable form’ (number followed by size unit like MB, MiB, GB or GiB, etc. or SIZE can be set zero to disable the cache.

Other Changes

Histogram Libraries

Math Libraries

TMVA Libraries

2D Graphics Libraries

3D Graphics Libraries

TRatioPlot has two constructors, one which accepts two histograms, and is responsible for setting up the calculation of ratios and differences. This calculation is in part delegated to TEfficiency. A single option can be given as a parameter, that is used to determine which procedure is chosen. The remaining option string is then passed through to the calculation, if applicable.

Several examples illustrate how to use this class. See: $ROOTSYS/tutorials/hist/ratioplot?.C

New histogram drawing options


COL2 is a new rendering technique providing potential performance improvements compared to the standard COL option. The performance comparison of the COL2 to the COL option depends on the histogram and the size of the rendering region in the current pad. In general, a small (approx. less than 100 bins per axis), sparsely populated TH2 will render faster with the COL option.

However, for larger histograms (approx. more than 100 bins per axis) that are not sparse, the COL2 option will provide up to 20 times performance improvements. For example, a 1000x1000 bin TH2 that is not sparse will render an order of magnitude faster with the COL2 option.

The COL2 option will also scale its performance based on the size of the pixmap the histogram image is being rendered into. It also is much better optimized for sessions where the user is forwarding X11 windows through an ssh connection.

For the most part, the COL2 and COLZ2 options are a drop in replacement to the COL and COLZ options. There is one major difference and that concerns the treatment of bins with zero content. The COL2 and COLZ2 options color these bins the color of zero.

This has been implemented by Jeromy Tompkins

Geometry Libraries

A new module geom/vecgeom was introduced to give transparent access to VecGeom solid primitives. VecGeom is a high performance geometry package (link) providing SIMD vectorization for the CPU-intensive geometry algorithms used for geometry navigation. The module creates a new library depending on the VecGeom main library and loaded using the ROOT plug-in mechanism.

The main functionality provided by the new vecgeom module is to make a conversion in memory of all the shapes in a loaded TGeo geometry into a special adapter shape TGeoVGShape, redirecting all navigation calls to the corresponding VecGeom solid. The library loading and geometry conversion can be done with a single call TVirtualGeoConverter::Instance()->ConvertGeometry()

After the conversion is done, all existing TGeo functionality is available as for a native geometry, only that most of the converted solids provide better navigation performance, despite the overhead introduced by the new adapter shape.

Prerequisites: installation of VecGeom. The installation instructions are available at Due to the fact that VecGeom provides for the moment static libraries and depends on ROOT, is is advised to compile first ROOT without VecGeom support, then compile VecGeom against this ROOT version, then re-configure ROOT to enable VecGeom and Vc support, using the flags -Dvc=ON -Dvecgeom=on

This has been implemented by Mihaela Gheata

Database Libraries

Networking Libraries

GUI Libraries

Language Bindings


Notebook integration

JavaScript ROOT

For more details, like the complete change log, the documentation, and very detailed examples, see the JSROOT home page and the JSROOT project github page


Build, Configuration and Testing Infrastructure

Release 6.08/02

Released on December 2, 2016



Bugs fixed in this release

Release 6.08/04

Released on January 13, 2017


Bugs fixed in this release

Release 6.08/06

Released on March 2, 2017






Bugs fixed in this release

HEAD of the v6-08-00-patches branch

Changes will be part of the future 6.08/08