diff --git a/applications/test/ListOps/Test-ListOps.C b/applications/test/ListOps/Test-ListOps.C
index e2739021b3..926d6e90f8 100644
--- a/applications/test/ListOps/Test-ListOps.C
+++ b/applications/test/ListOps/Test-ListOps.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2012-2013 OpenFOAM Foundation
-    Copyright (C) 2019 OpenCFD Ltd.
+    Copyright (C) 2019-2021 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -124,7 +124,7 @@ int main(int argc, char *argv[])
     std::for_each(test6.begin(), test6.end(), [](label& x){ x *= 3; });
 
     // Randomize the list
-    std::random_shuffle(test6.begin(), test6.end());
+    Foam::shuffle(test6);
 
     Info<< "randomized input list: " << flatOutput(test6) << nl;
 
@@ -160,7 +160,7 @@ int main(int argc, char *argv[])
 
     // List reorder
     labelList oldToNew(identity(40));
-    std::random_shuffle(oldToNew.begin(), oldToNew.end());
+    Foam::shuffle(oldToNew);
 
     // Force a few -1:
     oldToNew[4] = oldToNew[8] = -1;
@@ -192,9 +192,9 @@ int main(int argc, char *argv[])
         )
     );
 
-    Info<<"packed input: " << flatOutput(packed) << nl;
+    Info<< "packed input: " << packed << nl;
     inplaceReorder(oldToNew, packed);
-    Info<<"     reorder: " << flatOutput(packed) << nl << nl;
+    Info<<"     reorder: " << packed << nl << nl;
 
     Info<< "\nEnd\n" << endl;
 
diff --git a/applications/test/vector/Test-vector.C b/applications/test/vector/Test-vector.C
index 2a1e0675d5..2cfebcd81d 100644
--- a/applications/test/vector/Test-vector.C
+++ b/applications/test/vector/Test-vector.C
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2018-2019 OpenCFD Ltd.
+    Copyright (C) 2018-2021 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -34,6 +34,7 @@ Description
 #include "vector.H"
 #include "IOstreams.H"
 #include <algorithm>
+#include <random>
 
 using namespace Foam;
 
@@ -115,9 +116,8 @@ void testData(const VecSpace& vs)
 int main(int argc, char *argv[])
 {
     Info<<"normalised: " << vector(1,2,3).normalise() << nl;
-    Info<<"normalised: " << vector(VSMALL,VSMALL,VSMALL).normalise() << nl;
-    Info<<"normalised: " <<
-        vector(ROOTVSMALL,ROOTVSMALL,ROOTVSMALL).normalise() << nl;
+    Info<<"normalised: " << vector::uniform(VSMALL).normalise() << nl;
+    Info<<"normalised: " << vector::uniform(ROOTVSMALL).normalise() << nl;
 
     {
         vector vec1(0.5, 0.5, 0.5);
@@ -134,7 +134,7 @@ int main(int argc, char *argv[])
         std::sort(vec2.begin(), vec2.end());
         Info<< "sorted: " << vec2 << nl;
 
-        std::random_shuffle(vec2.begin(), vec2.end());
+        std::shuffle(vec2.begin(), vec2.end(), std::default_random_engine());
         Info<< "shuffled: " << vec2 << nl;
     }
 
diff --git a/applications/utilities/mesh/generation/foamyMesh/conformalVoronoiMesh/DelaunayMesh/DelaunayMesh.C b/applications/utilities/mesh/generation/foamyMesh/conformalVoronoiMesh/DelaunayMesh/DelaunayMesh.C
index 9ae95d5db8..192a7e4034 100644
--- a/applications/utilities/mesh/generation/foamyMesh/conformalVoronoiMesh/DelaunayMesh/DelaunayMesh.C
+++ b/applications/utilities/mesh/generation/foamyMesh/conformalVoronoiMesh/DelaunayMesh/DelaunayMesh.C
@@ -6,6 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2012-2015 OpenFOAM Foundation
+    Copyright (C) 2021 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -33,6 +34,8 @@ License
 #include "scalarIOField.H"
 #include "labelIOField.H"
 #include "pointConversion.H"
+#include <algorithm>
+#include <random>
 
 // * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
 
@@ -304,7 +307,7 @@ Foam::Map<Foam::label> Foam::DelaunayMesh<Triangulation>::rangeInsertWithInfo
         );
     }
 
-    std::random_shuffle(points.begin(), points.end());
+    std::shuffle(points.begin(), points.end(), std::default_random_engine());
 
     spatial_sort
     (
diff --git a/applications/utilities/mesh/generation/foamyMesh/conformalVoronoiMesh/DelaunayMesh/DistributedDelaunayMesh.C b/applications/utilities/mesh/generation/foamyMesh/conformalVoronoiMesh/DelaunayMesh/DistributedDelaunayMesh.C
index 56b18a898a..3a93a47583 100644
--- a/applications/utilities/mesh/generation/foamyMesh/conformalVoronoiMesh/DelaunayMesh/DistributedDelaunayMesh.C
+++ b/applications/utilities/mesh/generation/foamyMesh/conformalVoronoiMesh/DelaunayMesh/DistributedDelaunayMesh.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2012-2016 OpenFOAM Foundation
-    Copyright (C) 2020 OpenCFD Ltd.
+    Copyright (C) 2020-2021 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -33,6 +33,8 @@ License
 #include "pointConversion.H"
 #include "indexedVertexEnum.H"
 #include "IOmanip.H"
+#include <algorithm>
+#include <random>
 
 // * * * * * * * * * * * * Static Member Functions * * * * * * * * * * * * * //
 
@@ -880,7 +882,12 @@ Foam::DistributedDelaunayMesh<Triangulation>::rangeInsertReferredWithInfo
         );
     }
 
-    std::random_shuffle(pointsBbDistSqr.begin(), pointsBbDistSqr.end());
+    std::shuffle
+    (
+        pointsBbDistSqr.begin(),
+        pointsBbDistSqr.end(),
+        std::default_random_engine()
+    );
 
     // Sort in ascending order by the distance of the point from the centre
     // of the processor bounding box
diff --git a/src/OpenFOAM/containers/Bits/PackedList/PackedList.H b/src/OpenFOAM/containers/Bits/PackedList/PackedList.H
index 7c2bf50a77..c27a442ece 100644
--- a/src/OpenFOAM/containers/Bits/PackedList/PackedList.H
+++ b/src/OpenFOAM/containers/Bits/PackedList/PackedList.H
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2016 OpenFOAM Foundation
-    Copyright (C) 2017-2020 OpenCFD Ltd.
+    Copyright (C) 2017-2021 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -401,6 +401,10 @@ public:
         //- A pointer to the raw storage
         inline unsigned int* data() noexcept;
 
+        //- The number of bytes used in the raw storage
+        //- including any unused padding.
+        inline std::streamsize size_bytes() const noexcept;
+
         //- The number of bytes used in the raw storage
         //- including any unused padding.
         inline std::streamsize byteSize() const noexcept;
diff --git a/src/OpenFOAM/containers/Bits/PackedList/PackedListI.H b/src/OpenFOAM/containers/Bits/PackedList/PackedListI.H
index d52fc32eff..98e179b9cd 100644
--- a/src/OpenFOAM/containers/Bits/PackedList/PackedListI.H
+++ b/src/OpenFOAM/containers/Bits/PackedList/PackedListI.H
@@ -562,12 +562,19 @@ inline unsigned int* Foam::PackedList<Width>::data() noexcept
 
 
 template<unsigned Width>
-inline std::streamsize Foam::PackedList<Width>::byteSize() const noexcept
+inline std::streamsize Foam::PackedList<Width>::size_bytes() const noexcept
 {
     return num_blocks(size()) * sizeof(block_type);
 }
 
 
+template<unsigned Width>
+inline std::streamsize Foam::PackedList<Width>::byteSize() const noexcept
+{
+    return this->size_bytes();
+}
+
+
 template<unsigned Width>
 inline void Foam::PackedList<Width>::swap(PackedList<Width>& rhs)
 {
diff --git a/src/OpenFOAM/containers/Bits/PackedList/PackedListIO.C b/src/OpenFOAM/containers/Bits/PackedList/PackedListIO.C
index 45bb1c1fea..9bcf609c53 100644
--- a/src/OpenFOAM/containers/Bits/PackedList/PackedListIO.C
+++ b/src/OpenFOAM/containers/Bits/PackedList/PackedListIO.C
@@ -128,7 +128,7 @@ Foam::Istream& Foam::PackedList<Width>::read(Istream& is)
                 is.read
                 (
                     reinterpret_cast<char*>(list.data()),
-                    list.byteSize()
+                    list.size_bytes()
                 );
 
                 is.fatalCheck
@@ -230,7 +230,7 @@ Foam::Ostream& Foam::PackedList<Width>::writeList
             os.write
             (
                 reinterpret_cast<const char*>(list.cdata()),
-                list.byteSize()
+                list.size_bytes()
             );
         }
     }
diff --git a/src/OpenFOAM/containers/Bits/bitSet/bitSetIO.C b/src/OpenFOAM/containers/Bits/bitSet/bitSetIO.C
index 597e40ba0d..64032740d1 100644
--- a/src/OpenFOAM/containers/Bits/bitSet/bitSetIO.C
+++ b/src/OpenFOAM/containers/Bits/bitSet/bitSetIO.C
@@ -88,7 +88,7 @@ Foam::Ostream& Foam::bitSet::writeList
             os.write
             (
                 reinterpret_cast<const char*>(list.cdata()),
-                list.byteSize()
+                list.size_bytes()
             );
         }
     }
diff --git a/src/OpenFOAM/containers/Lists/FixedList/FixedList.C b/src/OpenFOAM/containers/Lists/FixedList/FixedList.C
index 6d0f5703d4..d0570f2a98 100644
--- a/src/OpenFOAM/containers/Lists/FixedList/FixedList.C
+++ b/src/OpenFOAM/containers/Lists/FixedList/FixedList.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2015 OpenFOAM Foundation
-    Copyright (C) 2017-2020 OpenCFD Ltd.
+    Copyright (C) 2017-2021 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -40,8 +40,7 @@ std::streamsize Foam::FixedList<T, N>::byteSize() const
             << "Invalid for non-contiguous data types"
             << abort(FatalError);
     }
-
-    return N*sizeof(T);
+    return this->size_bytes();
 }
 
 
diff --git a/src/OpenFOAM/containers/Lists/FixedList/FixedList.H b/src/OpenFOAM/containers/Lists/FixedList/FixedList.H
index 2378f152bc..a4406b5861 100644
--- a/src/OpenFOAM/containers/Lists/FixedList/FixedList.H
+++ b/src/OpenFOAM/containers/Lists/FixedList/FixedList.H
@@ -216,7 +216,12 @@ public:
         //- The last element of the list, position [N-1]
         inline const T& last() const noexcept;
 
-        //- The number of bytes stored by the list data for contiguous types
+        //- Number of contiguous bytes for the list data,
+        //- no runtime check that the type is actually contiguous
+        inline static std::streamsize size_bytes() noexcept;
+
+        //- Number of contiguous bytes for the list data,
+        //- with runtime check that the type is actually contiguous
         std::streamsize byteSize() const;
 
         //- Return the forward circular index, i.e. next index
diff --git a/src/OpenFOAM/containers/Lists/FixedList/FixedListI.H b/src/OpenFOAM/containers/Lists/FixedList/FixedListI.H
index 5bdcf55eb5..4f7d544e46 100644
--- a/src/OpenFOAM/containers/Lists/FixedList/FixedListI.H
+++ b/src/OpenFOAM/containers/Lists/FixedList/FixedListI.H
@@ -184,6 +184,13 @@ Foam::FixedList<T, N>::data() noexcept
 }
 
 
+template<class T, unsigned N>
+inline std::streamsize Foam::FixedList<T, N>::size_bytes() noexcept
+{
+    return N*sizeof(T);
+}
+
+
 template<class T, unsigned N>
 inline T& Foam::FixedList<T, N>::first() noexcept
 {
diff --git a/src/OpenFOAM/containers/Lists/List/List.C b/src/OpenFOAM/containers/Lists/List/List.C
index 302529f81f..c39f993934 100644
--- a/src/OpenFOAM/containers/Lists/List/List.C
+++ b/src/OpenFOAM/containers/Lists/List/List.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2016 OpenFOAM Foundation
-    Copyright (C) 2017-2020 OpenCFD Ltd.
+    Copyright (C) 2017-2021 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -199,7 +199,7 @@ Foam::List<T>::List(const UList<T>& a)
         {
             std::memcpy
             (
-                static_cast<void*>(this->v_), a.v_, this->byteSize()
+                static_cast<void*>(this->v_), a.v_, this->size_bytes()
             );
         }
         else
@@ -232,7 +232,7 @@ Foam::List<T>::List(const List<T>& a)
         {
             std::memcpy
             (
-                static_cast<void*>(this->v_), a.v_, this->byteSize()
+                static_cast<void*>(this->v_), a.v_, this->size_bytes()
             );
         }
         else
@@ -274,7 +274,7 @@ Foam::List<T>::List(List<T>& a, bool reuse)
         {
             std::memcpy
             (
-                static_cast<void*>(this->v_), a.v_, this->byteSize()
+                static_cast<void*>(this->v_), a.v_, this->size_bytes()
             );
         }
         else
@@ -516,7 +516,7 @@ void Foam::List<T>::operator=(const UList<T>& a)
         {
             std::memcpy
             (
-                static_cast<void*>(this->v_), a.v_, this->byteSize()
+                static_cast<void*>(this->v_), a.v_, this->size_bytes()
             );
         }
         else
diff --git a/src/OpenFOAM/containers/Lists/UList/UList.C b/src/OpenFOAM/containers/Lists/UList/UList.C
index 267a7b3269..41dbb8f036 100644
--- a/src/OpenFOAM/containers/Lists/UList/UList.C
+++ b/src/OpenFOAM/containers/Lists/UList/UList.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2016 OpenFOAM Foundation
-    Copyright (C) 2017-2020 OpenCFD Ltd.
+    Copyright (C) 2017-2021 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -32,6 +32,7 @@ License
 #include "labelRange.H"
 
 #include <algorithm>
+#include <random>
 
 // * * * * * * * * * * * * Protected Member Functions  * * * * * * * * * * * //
 
@@ -120,7 +121,7 @@ void Foam::UList<T>::deepCopy(const UList<T>& list)
         {
             std::memcpy
             (
-                static_cast<void*>(this->v_), list.v_, this->byteSize()
+                static_cast<void*>(this->v_), list.v_, this->size_bytes()
             );
         }
         else
@@ -196,8 +197,7 @@ std::streamsize Foam::UList<T>::byteSize() const
             << "Invalid for non-contiguous data types"
             << abort(FatalError);
     }
-
-    return this->size_*sizeof(T);
+    return this->size_bytes();
 }
 
 
@@ -281,7 +281,7 @@ void Foam::stableSort(UList<T>& a, const Compare& comp)
 template<class T>
 void Foam::shuffle(UList<T>& a)
 {
-    std::random_shuffle(a.begin(), a.end());
+    std::shuffle(a.begin(), a.end(), std::default_random_engine());
 }
 
 
diff --git a/src/OpenFOAM/containers/Lists/UList/UList.H b/src/OpenFOAM/containers/Lists/UList/UList.H
index fcdbc3d75a..c7b6a0cf1e 100644
--- a/src/OpenFOAM/containers/Lists/UList/UList.H
+++ b/src/OpenFOAM/containers/Lists/UList/UList.H
@@ -274,8 +274,12 @@ public:
             //- Return the last element of the list
             inline const T& last() const;
 
-            //- The number of bytes stored by the list data for contiguous types
-            //  \note is a std::streamsize since it is used in stream ops
+            //- Number of contiguous bytes for the List data,
+            //- no runtime check that the type is actually contiguous
+            inline std::streamsize size_bytes() const noexcept;
+
+            //- Number of contiguous bytes for the List data,
+            //- with runtime check that the type is actually contiguous
             std::streamsize byteSize() const;
 
 
@@ -530,7 +534,7 @@ public:
             {
                 if (is_contiguous<T>::value)
                 {
-                    return Hasher(obj.cdata(), obj.size()*sizeof(T), seed);
+                    return Hasher(obj.cdata(), obj.size_bytes(), seed);
                 }
 
                 for (const T& val : obj)
@@ -600,7 +604,7 @@ struct Hash<UList<T>>
     {
         if (is_contiguous<T>::value)
         {
-            return Hasher(obj.cdata(), obj.size()*sizeof(T), seed);
+            return Hasher(obj.cdata(), obj.size_bytes(), seed);
         }
         for (const T& val : obj)
         {
diff --git a/src/OpenFOAM/containers/Lists/UList/UListI.H b/src/OpenFOAM/containers/Lists/UList/UListI.H
index 9edb72fc6a..923e896f23 100644
--- a/src/OpenFOAM/containers/Lists/UList/UListI.H
+++ b/src/OpenFOAM/containers/Lists/UList/UListI.H
@@ -207,6 +207,13 @@ inline T* Foam::UList<T>::data() noexcept
 }
 
 
+template<class T>
+inline std::streamsize Foam::UList<T>::size_bytes() const noexcept
+{
+    return std::streamsize(size_)*sizeof(T);
+}
+
+
 template<class T>
 inline bool Foam::UList<T>::found(const T& val, label pos) const
 {
diff --git a/src/OpenFOAM/containers/Lists/UList/UListIO.C b/src/OpenFOAM/containers/Lists/UList/UListIO.C
index c77d98c0cf..6fc94df561 100644
--- a/src/OpenFOAM/containers/Lists/UList/UListIO.C
+++ b/src/OpenFOAM/containers/Lists/UList/UListIO.C
@@ -146,7 +146,7 @@ Foam::Ostream& Foam::UList<T>::writeList
             os.write
             (
                 reinterpret_cast<const char*>(list.cdata()),
-                list.byteSize()
+                list.size_bytes()
             );
         }
     }
diff --git a/src/OpenFOAM/db/IOobjects/decomposedBlockData/decomposedBlockData.C b/src/OpenFOAM/db/IOobjects/decomposedBlockData/decomposedBlockData.C
index 41234f7509..b4388efb1c 100644
--- a/src/OpenFOAM/db/IOobjects/decomposedBlockData/decomposedBlockData.C
+++ b/src/OpenFOAM/db/IOobjects/decomposedBlockData/decomposedBlockData.C
@@ -609,7 +609,7 @@ void Foam::decomposedBlockData::gather
     const label nProcs = UPstream::nProcs(comm);
     datas.setSize(nProcs);
 
-    char* data0Ptr = reinterpret_cast<char*>(datas.begin());
+    char* data0Ptr = reinterpret_cast<char*>(datas.data());
 
     List<int> recvOffsets;
     List<int> recvSizes;
@@ -682,15 +682,15 @@ void Foam::decomposedBlockData::gatherSlaveData
     )
     {
         // Note: UPstream::gather limited to int
-        nSend = int(data.byteSize());
+        nSend = int(data.size_bytes());
     }
 
     UPstream::gather
     (
-        data.begin(),
+        data.cdata(),
         nSend,
 
-        recvData.begin(),
+        recvData.data(),
         sliceSizes,
         sliceOffsets,
         comm
@@ -822,8 +822,8 @@ bool Foam::decomposedBlockData::writeBlocks
                 (
                     UPstream::commsTypes::scheduled,
                     proci,
-                    elems.begin(),
-                    elems.size(),
+                    elems.data(),
+                    elems.size_bytes(),
                     Pstream::msgType(),
                     comm
                 );
@@ -841,8 +841,8 @@ bool Foam::decomposedBlockData::writeBlocks
             (
                 UPstream::commsTypes::scheduled,
                 UPstream::masterNo(),
-                data.begin(),
-                data.byteSize(),
+                data.cdata(),
+                data.size_bytes(),
                 Pstream::msgType(),
                 comm
             );
@@ -1015,12 +1015,12 @@ bool Foam::decomposedBlockData::writeData(Ostream& os) const
     if (isA<OFstream>(os))
     {
         // Serial file output - can use writeRaw()
-        os.writeRaw(data.cdata(), data.byteSize());
+        os.writeRaw(data.cdata(), data.size_bytes());
     }
     else
     {
         // Other cases are less fortunate, and no std::string_view
-        std::string str(data.cdata(), data.byteSize());
+        std::string str(data.cdata(), data.size_bytes());
         os.writeQuoted(str, false);
     }
 
@@ -1052,7 +1052,7 @@ bool Foam::decomposedBlockData::writeObject
     }
 
     labelList recvSizes;
-    gather(comm_, label(this->byteSize()), recvSizes);
+    gather(comm_, label(this->size_bytes()), recvSizes);
 
     List<std::streamoff> start;
     PtrList<SubList<char>> slaveData;  // dummy slave data
diff --git a/src/OpenFOAM/db/IOstreams/Pstreams/UOPstream.C b/src/OpenFOAM/db/IOstreams/Pstreams/UOPstream.C
index e70e9cc1c0..82f72e866b 100644
--- a/src/OpenFOAM/db/IOstreams/Pstreams/UOPstream.C
+++ b/src/OpenFOAM/db/IOstreams/Pstreams/UOPstream.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2017 OpenFOAM Foundation
-    Copyright (C) 2016-2020 OpenCFD Ltd.
+    Copyright (C) 2016-2021 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -170,7 +170,7 @@ Foam::UOPstream::~UOPstream()
             (
                 commsType_,
                 toProcNo_,
-                sendBuf_.begin(),
+                sendBuf_.cdata(),
                 sendBuf_.size(),
                 tag_,
                 comm_
diff --git a/src/OpenFOAM/db/IOstreams/Pstreams/combineGatherScatter.C b/src/OpenFOAM/db/IOstreams/Pstreams/combineGatherScatter.C
index da30e43862..2e7627db90 100644
--- a/src/OpenFOAM/db/IOstreams/Pstreams/combineGatherScatter.C
+++ b/src/OpenFOAM/db/IOstreams/Pstreams/combineGatherScatter.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2017 OpenFOAM Foundation
-    Copyright (C) 2019-2020 OpenCFD Ltd.
+    Copyright (C) 2019-2021 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -314,7 +314,7 @@ void Foam::Pstream::listCombineGather
                     UPstream::commsTypes::scheduled,
                     belowID,
                     reinterpret_cast<char*>(receivedValues.data()),
-                    receivedValues.byteSize(),
+                    receivedValues.size_bytes(),
                     tag,
                     comm
                 );
@@ -371,7 +371,7 @@ void Foam::Pstream::listCombineGather
                     UPstream::commsTypes::scheduled,
                     myComm.above(),
                     reinterpret_cast<const char*>(Values.cdata()),
-                    Values.byteSize(),
+                    Values.size_bytes(),
                     tag,
                     comm
                 );
@@ -451,7 +451,7 @@ void Foam::Pstream::listCombineScatter
                     UPstream::commsTypes::scheduled,
                     myComm.above(),
                     reinterpret_cast<char*>(Values.data()),
-                    Values.byteSize(),
+                    Values.size_bytes(),
                     tag,
                     comm
                 );
@@ -493,7 +493,7 @@ void Foam::Pstream::listCombineScatter
                     UPstream::commsTypes::scheduled,
                     belowID,
                     reinterpret_cast<const char*>(Values.cdata()),
-                    Values.byteSize(),
+                    Values.size_bytes(),
                     tag,
                     comm
                 );
diff --git a/src/OpenFOAM/db/IOstreams/Pstreams/gatherScatterList.C b/src/OpenFOAM/db/IOstreams/Pstreams/gatherScatterList.C
index 5e392eba3b..a3282d1ece 100644
--- a/src/OpenFOAM/db/IOstreams/Pstreams/gatherScatterList.C
+++ b/src/OpenFOAM/db/IOstreams/Pstreams/gatherScatterList.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2017 OpenFOAM Foundation
-    Copyright (C) 2015-2020 OpenCFD Ltd.
+    Copyright (C) 2015-2021 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -85,7 +85,7 @@ void Pstream::gatherList
                     UPstream::commsTypes::scheduled,
                     belowID,
                     reinterpret_cast<char*>(receivedValues.data()),
-                    receivedValues.byteSize(),
+                    receivedValues.size_bytes(),
                     tag,
                     comm
                 );
@@ -161,7 +161,7 @@ void Pstream::gatherList
                     UPstream::commsTypes::scheduled,
                     myComm.above(),
                     reinterpret_cast<const char*>(sendingValues.cdata()),
-                    sendingValues.byteSize(),
+                    sendingValues.size_bytes(),
                     tag,
                     comm
                 );
@@ -247,7 +247,7 @@ void Pstream::scatterList
                     UPstream::commsTypes::scheduled,
                     myComm.above(),
                     reinterpret_cast<char*>(receivedValues.data()),
-                    receivedValues.byteSize(),
+                    receivedValues.size_bytes(),
                     tag,
                     comm
                 );
@@ -303,7 +303,7 @@ void Pstream::scatterList
                     UPstream::commsTypes::scheduled,
                     belowID,
                     reinterpret_cast<const char*>(sendingValues.cdata()),
-                    sendingValues.byteSize(),
+                    sendingValues.size_bytes(),
                     tag,
                     comm
                 );
diff --git a/src/OpenFOAM/global/fileOperations/collatedFileOperation/OFstreamCollator.C b/src/OpenFOAM/global/fileOperations/collatedFileOperation/OFstreamCollator.C
index fc3480bd80..2f146ea2eb 100644
--- a/src/OpenFOAM/global/fileOperations/collatedFileOperation/OFstreamCollator.C
+++ b/src/OpenFOAM/global/fileOperations/collatedFileOperation/OFstreamCollator.C
@@ -465,7 +465,7 @@ bool Foam::OFstreamCollator::write
                     UPstream::commsTypes::nonBlocking,
                     proci,
                     reinterpret_cast<char*>(slaveData[proci].data()),
-                    slaveData[proci].byteSize(),
+                    slaveData[proci].size_bytes(),
                     Pstream::msgType(),
                     localComm_
                 );
@@ -480,7 +480,7 @@ bool Foam::OFstreamCollator::write
                     UPstream::commsTypes::nonBlocking,
                     0,
                     reinterpret_cast<const char*>(slice.cdata()),
-                    slice.byteSize(),
+                    slice.size_bytes(),
                     Pstream::msgType(),
                     localComm_
                 )
@@ -489,7 +489,7 @@ bool Foam::OFstreamCollator::write
                 FatalErrorInFunction
                     << "Cannot send outgoing message. "
                     << "to:" << 0 << " nBytes:"
-                    << label(slice.byteSize())
+                    << label(slice.size_bytes())
                     << Foam::abort(FatalError);
             }
         }
diff --git a/src/OpenFOAM/matrices/Matrix/Matrix.C b/src/OpenFOAM/matrices/Matrix/Matrix.C
index 84a089b8cd..1a45c0460e 100644
--- a/src/OpenFOAM/matrices/Matrix/Matrix.C
+++ b/src/OpenFOAM/matrices/Matrix/Matrix.C
@@ -469,8 +469,7 @@ std::streamsize Foam::Matrix<Form, Type>::byteSize() const
             << "Invalid for non-contiguous data types"
             << abort(FatalError);
     }
-
-    return mRows_*nCols_*sizeof(Type);
+    return this->size_bytes();
 }
 
 
diff --git a/src/OpenFOAM/matrices/Matrix/Matrix.H b/src/OpenFOAM/matrices/Matrix/Matrix.H
index e77be53016..e6882cbbe7 100644
--- a/src/OpenFOAM/matrices/Matrix/Matrix.H
+++ b/src/OpenFOAM/matrices/Matrix/Matrix.H
@@ -204,7 +204,12 @@ public:
         //- be used to address into Matrix contents
         inline Type* data() noexcept;
 
-        //- The number of bytes stored by the Matrix data for contiguous types
+        //- Number of contiguous bytes for the Matrix data,
+        //- no runtime check that the type is actually contiguous
+        inline std::streamsize size_bytes() const noexcept;
+
+        //- Number of contiguous bytes for the Matrix data,
+        //- with runtime check that the type is actually contiguous
         std::streamsize byteSize() const;
 
         //- Return const pointer to data in the specified row
diff --git a/src/OpenFOAM/matrices/Matrix/MatrixI.H b/src/OpenFOAM/matrices/Matrix/MatrixI.H
index 29f988881e..4f0a269412 100644
--- a/src/OpenFOAM/matrices/Matrix/MatrixI.H
+++ b/src/OpenFOAM/matrices/Matrix/MatrixI.H
@@ -211,6 +211,13 @@ inline Type* Foam::Matrix<Form, Type>::data() noexcept
 }
 
 
+template<class Form, class Type>
+inline std::streamsize Foam::Matrix<Form, Type>::size_bytes() const noexcept
+{
+    return mRows_*nCols_*sizeof(Type);
+}
+
+
 template<class Form, class Type>
 inline const Type* Foam::Matrix<Form, Type>::rowData(const label irow) const
 {
diff --git a/src/OpenFOAM/matrices/lduMatrix/solvers/PPCG/PPCG.C b/src/OpenFOAM/matrices/lduMatrix/solvers/PPCG/PPCG.C
index 0f9a0ad748..d231a2daac 100644
--- a/src/OpenFOAM/matrices/lduMatrix/solvers/PPCG/PPCG.C
+++ b/src/OpenFOAM/matrices/lduMatrix/solvers/PPCG/PPCG.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2019-2020 Mattijs Janssens
-    Copyright (C) 2020 OpenCFD Ltd.
+    Copyright (C) 2020-2021 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -67,7 +67,7 @@ void Foam::PPCG::gSumMagProd
     {
         Foam::reduce
         (
-            globalSum.begin(),
+            globalSum.data(),
             globalSum.size(),
             sumOp<solveScalar>(),
             Pstream::msgType(),
diff --git a/src/OpenFOAM/meshes/polyMesh/globalMeshData/globalIndexTemplates.C b/src/OpenFOAM/meshes/polyMesh/globalMeshData/globalIndexTemplates.C
index 7b995adfa6..127d3688eb 100644
--- a/src/OpenFOAM/meshes/polyMesh/globalMeshData/globalIndexTemplates.C
+++ b/src/OpenFOAM/meshes/polyMesh/globalMeshData/globalIndexTemplates.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2013-2017 OpenFOAM Foundation
-    Copyright (C) 2019-2020 OpenCFD Ltd.
+    Copyright (C) 2019-2021 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -66,7 +66,7 @@ void Foam::globalIndex::gather
                         commsType,
                         procIDs[i],
                         reinterpret_cast<char*>(procSlot.data()),
-                        procSlot.byteSize(),
+                        procSlot.size_bytes(),
                         tag,
                         comm
                     );
@@ -133,7 +133,7 @@ void Foam::globalIndex::gather
                     commsType,
                     procIDs[0],
                     reinterpret_cast<const char*>(fld.cdata()),
-                    fld.byteSize(),
+                    fld.size_bytes(),
                     tag,
                     comm
                 );
@@ -170,7 +170,7 @@ void Foam::globalIndex::gather
                 commsType,
                 procIDs[0],
                 reinterpret_cast<const char*>(fld.cdata()),
-                fld.byteSize(),
+                fld.size_bytes(),
                 tag,
                 comm
             );
@@ -319,7 +319,7 @@ void Foam::globalIndex::scatter
                         commsType,
                         procIDs[i],
                         reinterpret_cast<const char*>(procSlot.cdata()),
-                        procSlot.byteSize(),
+                        procSlot.size_bytes(),
                         tag,
                         comm
                     );
@@ -366,7 +366,7 @@ void Foam::globalIndex::scatter
                     commsType,
                     procIDs[i],
                     reinterpret_cast<const char*>(procSlot.cdata()),
-                    procSlot.byteSize(),
+                    procSlot.size_bytes(),
                     tag,
                     comm
                 );
@@ -391,7 +391,7 @@ void Foam::globalIndex::scatter
                     commsType,
                     procIDs[0],
                     reinterpret_cast<char*>(fld.data()),
-                    fld.byteSize(),
+                    fld.size_bytes(),
                     tag,
                     comm
                 );
@@ -428,7 +428,7 @@ void Foam::globalIndex::scatter
                 commsType,
                 procIDs[0],
                 reinterpret_cast<char*>(fld.data()),
-                fld.byteSize(),
+                fld.size_bytes(),
                 tag,
                 comm
             );
diff --git a/src/OpenFOAM/meshes/polyMesh/globalMeshData/globalMeshData.C b/src/OpenFOAM/meshes/polyMesh/globalMeshData/globalMeshData.C
index b3f7aed676..3b98b0c996 100644
--- a/src/OpenFOAM/meshes/polyMesh/globalMeshData/globalMeshData.C
+++ b/src/OpenFOAM/meshes/polyMesh/globalMeshData/globalMeshData.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2017 OpenFOAM Foundation
-    Copyright (C) 2015-2020 OpenCFD Ltd.
+    Copyright (C) 2015-2021 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -1920,7 +1920,7 @@ Foam::pointField Foam::globalMeshData::sharedPoints() const
             (
                 Pstream::commsTypes::blocking,
                 slave,
-                sharedPoints.size()*sizeof(Foam::vector)  // byteSize()
+                sharedPoints.size_bytes()
             );
             toSlave << sharedPoints;
         }
diff --git a/src/OpenFOAM/meshes/polyMesh/mapPolyMesh/mapDistribute/mapDistributeBaseTemplates.C b/src/OpenFOAM/meshes/polyMesh/mapPolyMesh/mapDistribute/mapDistributeBaseTemplates.C
index 43c2e6c29a..61813efd66 100644
--- a/src/OpenFOAM/meshes/polyMesh/mapPolyMesh/mapDistribute/mapDistributeBaseTemplates.C
+++ b/src/OpenFOAM/meshes/polyMesh/mapPolyMesh/mapDistribute/mapDistributeBaseTemplates.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2015-2017 OpenFOAM Foundation
-    Copyright (C) 2015-2020 OpenCFD Ltd.
+    Copyright (C) 2015-2021 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -536,7 +536,7 @@ void Foam::mapDistributeBase::distribute
                         Pstream::commsTypes::nonBlocking,
                         domain,
                         reinterpret_cast<const char*>(subField.cdata()),
-                        subField.byteSize(),
+                        subField.size_bytes(),
                         tag,
                         comm
                     );
@@ -559,7 +559,7 @@ void Foam::mapDistributeBase::distribute
                         Pstream::commsTypes::nonBlocking,
                         domain,
                         reinterpret_cast<char*>(recvFields[domain].data()),
-                        recvFields[domain].byteSize(),
+                        recvFields[domain].size_bytes(),
                         tag,
                         comm
                     );
@@ -1061,7 +1061,7 @@ void Foam::mapDistributeBase::distribute
                         Pstream::commsTypes::nonBlocking,
                         domain,
                         reinterpret_cast<const char*>(subField.cdata()),
-                        subField.size()*sizeof(T),
+                        subField.size_bytes(),
                         tag,
                         comm
                     );
@@ -1084,7 +1084,7 @@ void Foam::mapDistributeBase::distribute
                         Pstream::commsTypes::nonBlocking,
                         domain,
                         reinterpret_cast<char*>(recvFields[domain].data()),
-                        recvFields[domain].size()*sizeof(T),
+                        recvFields[domain].size_bytes(),
                         tag,
                         comm
                     );
diff --git a/src/OpenFOAM/meshes/polyMesh/syncTools/syncToolsTemplates.C b/src/OpenFOAM/meshes/polyMesh/syncTools/syncToolsTemplates.C
index 0392a0f0cc..8e9d91dfd0 100644
--- a/src/OpenFOAM/meshes/polyMesh/syncTools/syncToolsTemplates.C
+++ b/src/OpenFOAM/meshes/polyMesh/syncTools/syncToolsTemplates.C
@@ -1053,7 +1053,7 @@ void Foam::syncTools::syncBoundaryFaceList
                         Pstream::commsTypes::nonBlocking,
                         procPatch.neighbProcNo(),
                         reinterpret_cast<char*>(fld.data()),
-                        fld.byteSize()
+                        fld.size_bytes()
                     );
                 }
             }
@@ -1079,7 +1079,7 @@ void Foam::syncTools::syncBoundaryFaceList
                         Pstream::commsTypes::nonBlocking,
                         procPatch.neighbProcNo(),
                         reinterpret_cast<const char*>(fld.cdata()),
-                        fld.byteSize()
+                        fld.size_bytes()
                     );
                 }
             }
@@ -1280,7 +1280,7 @@ void Foam::syncTools::syncFaceList
                     Pstream::commsTypes::nonBlocking,
                     procPatch.neighbProcNo(),
                     reinterpret_cast<char*>(recvInfo.data()),
-                    recvInfo.byteSize()
+                    recvInfo.size_bytes()
                 );
             }
         }
@@ -1315,7 +1315,7 @@ void Foam::syncTools::syncFaceList
                     Pstream::commsTypes::nonBlocking,
                     procPatch.neighbProcNo(),
                     reinterpret_cast<const char*>(sendInfo.cdata()),
-                    sendInfo.byteSize()
+                    sendInfo.size_bytes()
                 );
             }
         }
diff --git a/src/OpenFOAM/primitives/Pair/Pair.H b/src/OpenFOAM/primitives/Pair/Pair.H
index 5b9dd491fc..7420d1bfc5 100644
--- a/src/OpenFOAM/primitives/Pair/Pair.H
+++ b/src/OpenFOAM/primitives/Pair/Pair.H
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2016 OpenFOAM Foundation
-    Copyright (C) 2017-2020 OpenCFD Ltd.
+    Copyright (C) 2017-2021 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -200,7 +200,7 @@ struct Hash<Pair<T>>
     {
         if (is_contiguous<T>::value)
         {
-            return Hasher(obj.cdata(), sizeof(obj), seed);
+            return Hasher(obj.cdata(), obj.size_bytes(), seed);
         }
 
         seed = Hash<T>()(obj.first(), seed);
diff --git a/src/OpenFOAM/primitives/Scalar/doubleFloat.H b/src/OpenFOAM/primitives/Scalar/doubleFloat.H
index 945b08fc13..7767088e51 100644
--- a/src/OpenFOAM/primitives/Scalar/doubleFloat.H
+++ b/src/OpenFOAM/primitives/Scalar/doubleFloat.H
@@ -73,6 +73,8 @@ MAXMINPOW(float, int, float)
 MAXMINPOW(float, float, long)
 MAXMINPOW(float, long, float)
 #if defined(__APPLE__) && WM_LABEL_SIZE == 64
+MAXMINPOW(double, double, int64_t)
+MAXMINPOW(double, int64_t, double)
 MAXMINPOW(float, float, int64_t)
 MAXMINPOW(float, int64_t, float)
 #endif
diff --git a/src/Pstream/mpi/UIPread.C b/src/Pstream/mpi/UIPread.C
index 4761b813b9..5fed1729e3 100644
--- a/src/Pstream/mpi/UIPread.C
+++ b/src/Pstream/mpi/UIPread.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2017 OpenFOAM Foundation
-    Copyright (C) 2019 OpenCFD Ltd.
+    Copyright (C) 2019-2021 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -115,7 +115,7 @@ Foam::UIPstream::UIPstream
         (
             commsType,
             fromProcNo_,
-            externalBuf_.begin(),
+            externalBuf_.data(),
             wantedSize,
             tag_,
             comm_
@@ -221,7 +221,7 @@ Foam::UIPstream::UIPstream(const int fromProcNo, PstreamBuffers& buffers)
         (
             commsType(),
             fromProcNo_,
-            externalBuf_.begin(),
+            externalBuf_.data(),
             wantedSize,
             tag_,
             comm_
diff --git a/src/Pstream/mpi/UPstream.C b/src/Pstream/mpi/UPstream.C
index 0964e754cc..c19ee6bad0 100644
--- a/src/Pstream/mpi/UPstream.C
+++ b/src/Pstream/mpi/UPstream.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2017 OpenFOAM Foundation
-    Copyright (C) 2016-2020 OpenCFD Ltd.
+    Copyright (C) 2016-2021 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -770,10 +770,10 @@ void Foam::UPstream::allToAll
             (
                 // NOTE: const_cast is a temporary hack for
                 // backward-compatibility with versions of OpenMPI < 1.7.4
-                const_cast<label*>(sendData.begin()),
+                const_cast<label*>(sendData.cdata()),
                 sizeof(label),
                 MPI_BYTE,
-                recvData.begin(),
+                recvData.data(),
                 sizeof(label),
                 MPI_BYTE,
                 PstreamGlobals::MPICommunicators_[communicator]
@@ -1090,7 +1090,7 @@ void Foam::UPstream::allocatePstreamCommunicator
         (
             PstreamGlobals::MPIGroups_[parentIndex],
             procIDs_[index].size(),
-            procIDs_[index].begin(),
+            procIDs_[index].cdata(),
            &PstreamGlobals::MPIGroups_[index]
         );
 
@@ -1188,7 +1188,7 @@ void Foam::UPstream::waitRequests(const label start)
             MPI_Waitall
             (
                 waitRequests.size(),
-                waitRequests.begin(),
+                waitRequests.data(),
                 MPI_STATUSES_IGNORE
             )
         )
diff --git a/src/conversion/ccm/reader/ccmReader.C b/src/conversion/ccm/reader/ccmReader.C
index 845735eee1..4a36f83921 100644
--- a/src/conversion/ccm/reader/ccmReader.C
+++ b/src/conversion/ccm/reader/ccmReader.C
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2016-2020 OpenCFD Ltd.
+    Copyright (C) 2016-2021 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -184,7 +184,7 @@ void Foam::ccm::reader::readMap
     (
         &(globalState_->error),
         mapId,
-        data.begin(),
+        data.data(),
         kCCMIOStart,
         kCCMIOEnd
     );
diff --git a/src/conversion/ccm/reader/ccmReaderMesh.C b/src/conversion/ccm/reader/ccmReaderMesh.C
index f621a5cadc..7b8279afed 100644
--- a/src/conversion/ccm/reader/ccmReaderMesh.C
+++ b/src/conversion/ccm/reader/ccmReaderMesh.C
@@ -42,7 +42,6 @@ License
 
 #include "ccmInternal.H" // include last to avoid any strange interactions
 
-
 // * * * * * * * * * * * * * Private Member Functions  * * * * * * * * * * * //
 
 Foam::labelList Foam::ccm::reader::patchStartList(label initial) const
@@ -311,7 +310,7 @@ Foam::labelList Foam::ccm::reader::readVertices
         nullptr,
         nullptr,
         nullptr,
-        vrts.begin(),
+        vrts.data(),
         kCCMIOStart,
         kCCMIOEnd
     );
@@ -388,7 +387,7 @@ void Foam::ccm::reader::readCells
         &(globalState_->error),
         cellsNode,
         &mapId,
-        cellTableId_.begin(),
+        cellTableId_.data(),
         kCCMIOStart,
         kCCMIOEnd
     );
@@ -597,7 +596,7 @@ void Foam::ccm::reader::readCells
         kCCMIOInternalFaces,
         nullptr,
         nullptr,
-        ccmFaces.begin(),
+        ccmFaces.data(),
         kCCMIOStart,
         kCCMIOEnd
     );
@@ -607,7 +606,7 @@ void Foam::ccm::reader::readCells
         &(globalState_->error),
         nodeId,
         kCCMIOInternalFaces,
-        faceCells.begin(),
+        faceCells.data(),
         kCCMIOStart,
         kCCMIOEnd
     );
@@ -686,7 +685,7 @@ void Foam::ccm::reader::readCells
                 kCCMIOBoundaryFaces,
                 nullptr,
                 nullptr,
-                ccmFaces.begin(),
+                ccmFaces.data(),
                 kCCMIOStart,
                 kCCMIOEnd
             );
@@ -695,7 +694,7 @@ void Foam::ccm::reader::readCells
                 &(globalState_->error),
                 nodeId,
                 kCCMIOBoundaryFaces,
-                faceCells.begin(),
+                faceCells.data(),
                 kCCMIOStart,
                 kCCMIOEnd
             );
@@ -837,7 +836,7 @@ void Foam::ccm::reader::readInterfaces
             &(globalState_->error),
             interfaceNode,
             "ProstarBaffles",
-            mapData.begin(),
+            mapData.data(),
             kCCMIOStart,
             kCCMIOEnd
         );
@@ -880,7 +879,7 @@ void Foam::ccm::reader::readInterfaces
         &(globalState_->error),
         interfaceNode,
         "FaceIds",
-        mapData.begin(),
+        mapData.data(),
         kCCMIOStart,
         kCCMIOEnd
     );
@@ -1058,7 +1057,7 @@ void Foam::ccm::reader::readMonitoring
             // CCMIOGetNode(nullptr, childNode, "Cells", &subNode);
             // CCMIORead1i
             // (
-            //     nullptr, subNode, faceCells.begin(),
+            //     nullptr, subNode, faceCells.data(),
             //     kCCMIOStart, kCCMIOEnd
             // );
             //
diff --git a/src/conversion/ccm/reader/ccmReaderSolution.C b/src/conversion/ccm/reader/ccmReaderSolution.C
index 349e539fdf..7a1dcad594 100644
--- a/src/conversion/ccm/reader/ccmReaderSolution.C
+++ b/src/conversion/ccm/reader/ccmReaderSolution.C
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2016 OpenCFD Ltd.
+    Copyright (C) 2016-2021 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -542,7 +542,6 @@ Foam::ccm::reader::readField
                          && dataLocation == requestedLocation
                         )
                         {
-
 #ifdef SOLID_STRESS_HACK
                             bool okayCombination = true;
 
@@ -611,7 +610,7 @@ Foam::ccm::reader::readField
                                 dataNode,
                                 nullptr,
                                 nullptr,
-                                rawData.begin(),
+                                rawData.data(),
                                 kCCMIOStart,
                                 kCCMIOEnd
                             );
@@ -627,7 +626,6 @@ Foam::ccm::reader::readField
                                 const label cellId = mapData[i];
                                 scalarData[cellId] = rawData[i];
                             }
-
                         }
                     }
                 }
diff --git a/src/conversion/ccm/writer/ccmWriter.C b/src/conversion/ccm/writer/ccmWriter.C
index 19c7323c16..33f12e1f56 100644
--- a/src/conversion/ccm/writer/ccmWriter.C
+++ b/src/conversion/ccm/writer/ccmWriter.C
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2016-2020 OpenCFD Ltd.
+    Copyright (C) 2016-2021 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -74,7 +74,7 @@ void Foam::ccm::writer::addLinearMap
         mapId,
         size,
         (start + size),
-        data.begin(),
+        data.cdata(),
         kCCMIOStart,
         kCCMIOEnd
     );
diff --git a/src/conversion/ccm/writer/ccmWriterMesh.C b/src/conversion/ccm/writer/ccmWriterMesh.C
index 7eb086b922..79f9df0139 100644
--- a/src/conversion/ccm/writer/ccmWriterMesh.C
+++ b/src/conversion/ccm/writer/ccmWriterMesh.C
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2016 OpenCFD Ltd.
+    Copyright (C) 2016-2021 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -175,7 +175,7 @@ void Foam::ccm::writer::writeFaces
         nodeType,
         mapId,
         streamSize,
-        ccmStream.begin(),
+        ccmStream.cdata(),
         kCCMIOStart,
         kCCMIOEnd
     );
@@ -235,7 +235,7 @@ void Foam::ccm::writer::writeFaces
         nodeId,
         nodeType,
         mapId,
-        ccmStream.begin(),
+        ccmStream.cdata(),
         kCCMIOStart,
         kCCMIOEnd
     );
@@ -262,7 +262,7 @@ void Foam::ccm::writer::writeFaces
             nodeId,
             "ProstarFaceId",
             size,
-            ccmStream.begin(),
+            ccmStream.cdata(),
             kCCMIOStart,
             kCCMIOEnd
         );
@@ -290,7 +290,7 @@ void Foam::ccm::writer::writeFaces
             "ProstarFaceId",
             size,
             2,
-            ccmStream.begin(),
+            ccmStream.cdata(),
             kCCMIOStart,
             kCCMIOEnd
         );
@@ -337,7 +337,7 @@ void Foam::ccm::writer::writeVertices
         verticesNode,
         3, scaling,
         vertexMap,
-        vrts.begin(),
+        vrts.cdata(),
         kCCMIOStart,
         kCCMIOEnd
     );
@@ -612,7 +612,7 @@ void Foam::ccm::writer::writeCells
         &(globalState_->error),
         cellsNode,
         maps_->cells,
-        mapData.begin(),
+        mapData.data(),
         kCCMIOStart, kCCMIOEnd
     );
     assertNoError("writing 'Cells' node");
@@ -640,7 +640,7 @@ void Foam::ccm::writer::writeCells
         cellsNode,
         "CellTopologyType",
         mesh_.nCells(),
-        mapData.begin(),
+        mapData.cdata(),
         kCCMIOStart, kCCMIOEnd
     );
 
@@ -701,7 +701,7 @@ void Foam::ccm::writer::writeInterfaces
                 "FaceIds",
                 interfaces.size(),
                 2,
-                mapData.begin(), kCCMIOStart, kCCMIOEnd
+                mapData.cdata(), kCCMIOStart, kCCMIOEnd
             )
          != kCCMIONoErr
         )
diff --git a/src/conversion/ccm/writer/ccmWriterSolution.C b/src/conversion/ccm/writer/ccmWriterSolution.C
index 0d52d04d43..accfa07a6b 100644
--- a/src/conversion/ccm/writer/ccmWriterSolution.C
+++ b/src/conversion/ccm/writer/ccmWriterSolution.C
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2016-2018 OpenCFD Ltd.
+    Copyright (C) 2016-2021 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -737,7 +737,7 @@ void Foam::ccm::writer::writeSolution
                 kCCMIOFace,
                 const_cast<scalar*>
                 (
-                    field.primitiveField().begin()
+                    field.primitiveField().cdata()
                 ),
                 kCCMIOStart,
                 kCCMIOEnd
@@ -762,7 +762,10 @@ void Foam::ccm::writer::writeSolution
                     nodeId,
                     maps_->boundary[patchI],
                     kCCMIOFace,
-                    field.boundaryField()[patchI].begin(),
+                    const_cast<scalar*>
+                    (
+                        field.boundaryField()[patchI].cdata()
+                    ),
                     kCCMIOStart,
                     kCCMIOEnd
                 );
diff --git a/src/overset/lduPrimitiveProcessorInterface/calculatedProcessorFvPatchField.C b/src/overset/lduPrimitiveProcessorInterface/calculatedProcessorFvPatchField.C
index 2c1f511b6c..5d0b4f30c7 100644
--- a/src/overset/lduPrimitiveProcessorInterface/calculatedProcessorFvPatchField.C
+++ b/src/overset/lduPrimitiveProcessorInterface/calculatedProcessorFvPatchField.C
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2019 OpenCFD Ltd.
+    Copyright (C) 2019-2021 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -170,7 +170,7 @@ void Foam::calculatedProcessorFvPatchField<Type>::initEvaluate
         (
             Pstream::commsTypes::nonBlocking,
             procInterface_.neighbProcNo(),
-            reinterpret_cast<char*>(this->begin()),
+            reinterpret_cast<char*>(this->data()),
             this->byteSize(),
             procInterface_.tag(),
             procInterface_.comm()
@@ -181,7 +181,7 @@ void Foam::calculatedProcessorFvPatchField<Type>::initEvaluate
         (
             Pstream::commsTypes::nonBlocking,
             procInterface_.neighbProcNo(),
-            reinterpret_cast<const char*>(sendBuf_.begin()),
+            reinterpret_cast<const char*>(sendBuf_.cdata()),
             this->byteSize(),
             procInterface_.tag(),
             procInterface_.comm()
@@ -246,7 +246,7 @@ void Foam::calculatedProcessorFvPatchField<Type>::initInterfaceMatrixUpdate
     (
         Pstream::commsTypes::nonBlocking,
         procInterface_.neighbProcNo(),
-        reinterpret_cast<char*>(scalarReceiveBuf_.begin()),
+        reinterpret_cast<char*>(scalarReceiveBuf_.data()),
         scalarReceiveBuf_.byteSize(),
         procInterface_.tag(),
         procInterface_.comm()
@@ -257,7 +257,7 @@ void Foam::calculatedProcessorFvPatchField<Type>::initInterfaceMatrixUpdate
     (
         Pstream::commsTypes::nonBlocking,
         procInterface_.neighbProcNo(),
-        reinterpret_cast<const char*>(scalarSendBuf_.begin()),
+        reinterpret_cast<const char*>(scalarSendBuf_.cdata()),
         scalarSendBuf_.byteSize(),
         procInterface_.tag(),
         procInterface_.comm()