Trap is known as Non-Maskable interrupts, which is used in emergency condition.

SIM is Set Interrupt Mask. Used to mask the hardware interrupts. RIM is Read Interrupt Mask. Used to check whether the interrupt is Masked or not.

An interrupt that can be turned off by the programmer is known as Maskable interrupt.

An interrupt which can be never be turned off (ie. disabled) is known as Non-Maskable interrupt

Missing expansion-slot covers adversely affect the system in two ways. First, the missing cover permits dust to accumulate in the system, forming an insulating blanket that traps heat next to active devices and causes them to overheat. Second, the heat problem is complicated further by the fact that the missing slot cover interrupts the designed airflow patterns inside the case, causing components to overheat because of missing or inadequate airflow.

There are two system board-based conditions that will cause a Non-Maskable Interrupt (NMI) signal to be sent to the microprocessor. The first condition occurs when an active IO Channel Check (IOCHCK) signal is received from an adapter card located in one of the board's expansion slots. The other event that will cause an NMI signal to be generated is the occurrence of a Parity Check (PCK) error in the system's DRAM memory.

IRQ (Interrupt Request) is a signal to a computer from a hardware device indicating that it's requesting some service from  the computer. Each request is carried along a circuit called IRQ line.