The basic data elements of HBOOK are the histogram (one- and two-dimensional) and the Ntuple. The user identifies his data elements using a single integer. Each of the elements has a number of attributes associated with it.
The package is organised as part of a library, from which at load time unsatisfied externals are searched and loaded. In this way only those subroutines actually used will be loaded, therefore minimising the space occupied in memory by the code. Unfortunately, given the way Fortran works and although the package is structured as much as possible in the sense of selective loading, some unused subroutines will usually be present.
HBOOK uses the ZEBRA [10] data structure
management package to manage its memory (see chapter 
).
The working space of HBOOK is an array, allocated to the labelled
common /PAWC/.
In ZEBRA terms this is a ZEBRA store.
It is thus necessary to reserve as many locations as required with a
declarative statement in the main program.
The actual length of the common is defined most safely via
a PARAMETER statement, as shown below:
| PARAMETER (NWPAWC = 50000) |
| COMMON /PAWC/ HMEMOR(NWPAWC) |
Furthermore HBOOK must be informed of the storage limit via a call to HLIMIT. This is discussed in detail in section . In the case above this would correspond to
CALL HLIMIT(NWPAWC)
[HLIMIT]
At execution time, when histograms are booked, they are accomodated
in common /PAWC/ in booking order, up to the maximum size available.
Note that a call to HLIMIT will automatically initialise the ZEBRA system via a call to the routine MZEBRA. If ZEBRA has already been initialised, (MZEBRA has already been called), then HLIMIT should be called with a negative number indicating the number of words required, e.g.
CALL HLIMIT(-NWPAWC)
[HLIMIT]