SCSI is usually used for external devices like CD-ROM drives and scanners. COM1 and COM3 are logically joined, while COM2 and COM4 are logically joined. COM1 and COM3 use IRQ4 while COM2 and COM4 use IRQ3. IRQ14 is the primary drive controller, and IRQ15 is the secondary drive controller. When IRQ2 cascades to IRQ9, number 2 can't be used.
Laser printers use a primary corona wire to charge the drum.
The drum is cleaned, charged, and written to. Paper is charged and pulls toner from the drum, where it's fused by the fuser rollers. If the heat-sensor on the fuser shuts down, the toner will fail to stick to the paper. Paper jams are usually caused by a bad separator pad. Sectors are 512 bytes.