A reserved printer is a printer to which only D3 can print.
A printer can be attached to a serial or parallel port and reserved for a D3 virtual machine. Reserved printers are managed by the D3 spooler which submits jobs to D3 printer processes serving specified form queues. A reserved printer can be defined and started in a user-defined macro called user-coldstart in the dm account. This macro is used automatically during a coldstart or the normal boot process.