The environment affecting a building presents external loads of different kinds on the VB (i.e. loads from weather, city resources supply systems, sunlight access etc.), as does the usage of the building (i.e. change in utilization, user comfort profiles, user services and maintenance demands).

One external load, 'access load', rarely considered, is derived from the fact that digital data has a limited access life time,

Floppy history

• 1970s - 8 inch one sided floppy, 100 kbytes
• 1973 - 8 inch two-sided floppy, 250 kbytes
• 1976 - Shugart introduces 5.25 inch diskett. 100 kbytes (later 1.2 Mbytes). (The onde sided diskett could be 'holed' and used two sided)
• 1980s - Sony introduces todays 3.5 inch diskett (today 1.5 Mbytes)