// Here is the file header format as of release 3.02.06. It is never compressed.
// -----------------------------------
// byte 0->3 "root" = Identifies this file as a ROOT file.
// 4->7 Version = File format version TFile::fVersion
// | (10000*major+100*minor+cycle (e.g. 30203 for 3.2.3))
// 8->11 BEGIN = Byte offset of first data record (64) TFile::fBEGIN
// 12->15 END = Pointer to first free word at the EOF TFile::fEND
// | (will be == to file size in bytes)
// 16->19 SeekFree = Byte offset of FreeSegments record TFile::fSeekFree
// 20->23 NbytesFree = Number of bytes in FreeSegments record TFile::fNBytesFree
// 24->27 nfree = Number of free data records
// 28->31 NbytesName = Number of bytes in TKey+TNamed for TFile at creation TDirectory::fNbytesName
// 32->32 Units = Number of bytes for file pointers (4) TFile::fUnits
// 33->36 Compress = Zip compression level (i.e. 0-9) TFile::fCompress
// 37->40 SeekInfo = Byte offset of StreamerInfo record TFile::fSeekInfo
// 41->44 NbytesInfo = Number of bytes in StreamerInfo record TFile::fNbytesInfo
// 45->63 = Unused??