less noise and less wasted energy in the friction losses inherent in the previously common drive shafts and their associated gearing. Also, maintenance was simpler and cheaper, and it was a more convenient method for the arrangement of power drives such that if one part were to fail then it would not cause loss of power to all sections of a factory or mill. These systems were in turn superseded in popularity by rope drive methods. Near the end of the 19th century some factories had a mile or more of line shafts in a single building. In order to provide power for small shops and light industry, specially constructed "power buildings" were constructed. Power buildings used a central steam engine and distributed power through line shafts to all the leased rooms. Power buildings continued to be built in the early days of electrification, still using line shafts but driven by an electric motor. As some factories grew too large and complex to be powered by a single steam engine, a system of "sub divided" power came into use. This was also important when a wide range of speed control was necessary for a sensitive operation such as wire drawing or hammering iron. Under sub divided power, steam was piped from a central boiler to smaller steam engines located where needed. However, small steam engines were much less efficient than large ones. The Baldwin Locomotive Works 63-acre site changed to sub divided power, then because of the inefficiency converted to group drive with several large steam engines driving the line shafts. Eventually Baldwin converted to electric drive, with a substantial saving in labor and building space. With factory electrification in the early 1900s, many line shafts began converting to electric drive. In early factory electrification only large motors were available, so new factories installed a large motor to drive line shafting and millwork. After 1900 smaller industrial motors became available and most new installations used individual electric drives. Steam turbine powered line shafts were commonly used to drive paper machines for speed control reasons until economical methods for precision electric motor speed control became available in the 1980s; since then many have been replaced with sectional electric drives. Economical variable speed control using electric motors was made possible by silicon controlled rectifiers (SCRs) to produce direct current and variable frequency drives using inverters to change DC back to AC at