__VAX_MAXDISKS
#define DISKUNIT(dev) ((minor(dev) / OLDMAXPARTITIONS) % __VAX_MAXDISKS)
((minor(dev) / (__VAX_MAXDISKS * OLDMAXPARTITIONS)) * OLDMAXPARTITIONS))
((part) / OLDMAXPARTITIONS) * (__VAX_MAXDISKS * OLDMAXPARTITIONS))