Of recent years there has appeared another class of switchboards, employing in some measure the features of the automatic and in some measure those of the manual switchboard.  These boards are commonly referred to as semi-automatic switchboards, presumably because they are supposed to be half automatic and half manual.

Manual.  Manual switchboards may be subdivided into two classes according to the method of distributing energy for talking purposes.  Thus we may have magneto switchboards, which are those capable of serving lines equipped with magneto telephones, local batteries being used for talking purposes.  On the other hand, we may have common-battery switchboards, adapted to connect lines employing common-battery telephones in which all the current for both talking and signaling is furnished from the central office.  In still another way we may classify manual switchboards if the method of distributing the energy for talking and signaling purposes is ignored.  Thus, entirely irrespective of whether the switchboards are adapted to serve common-battery or local-battery lines, we may have non-multiple switchboards and multiple switchboards.

The term multiple switchboard is applied to that class of switchboards in which the connection terminals or jacks for all the lines are repeated at intervals along the face of the switchboard, so that each operator may have within her reach a terminal for each line and may thus be able to complete by herself any connection between two lines terminating in the switchboard.

The term non-multiple switchboard is applied to that class of boards where the provision for repeating the line terminals at intervals along the face of the board is not employed, but where, as a consequence, each line has but a single terminal on the face of the board.  Non-multiple switchboards have their main use in small exchanges where not more than a few hundred lines terminate.  Where such is the case, it is an easy matter to handle all the traffic by one, two, or three operators, and as all of these operators may reach all over the face of the switchboard, there is no need for giving any line any more than one connection terminal.  Such boards may be called simple switchboards.

There is another type of non-multiple switchboard adaptable for use in larger exchanges than the simple switchboard.  A correct idea of the fundamental principle involved in these may be had by imagining a row of simple switchboards each containing terminals or jacks for its own group of lines.  In order to provide for the connection of a line in one of these simple switchboards with a line in another one, out of reach of the operator at the first, short connecting lines extending between the two switchboards are provided, these being called transfer or trunk lines.  In order that connections may be made between any two of the simple boards, a group of transfer lines is run from each board to every other one.