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81 My PC diagnostic utility lists "Cascade" amongst the hardware interrupts (IRQs). Does this mean I have the Cascade virus?




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This article is from the Computer Viruses FAQ, by Nick FitzGerald n.fitzgerald@csc.canterbury.ac.nz with numerous contributions by others.

81 My PC diagnostic utility lists "Cascade" amongst the hardware interrupts (IRQs). Does this mean I have the Cascade virus?

No! This is quite normal on AT-style (286 and better) PCs (and on a few
8086 (XT) class machines). The original IBM PC design had one
Programmable Interrupt Controller (PIC) to handle hardware interrupts
generated when devices like disk controllers, serial and parallel ports,
LAN adaptors, etc have to be serviced. While developing the AT, IBM
decided that the eight Interrupt ReQuest (IRQ) lines the original PIC
supported were probably insufficient for likely future expansion needs,
so they added a second PIC. The two PIC's had to cooperate, so both
didn't interrupt the CPU concurrently. This was achieved by having the
second PIC use an IRQ to signal the first PIC when it has an IRQ to
service. IRQs 2 and 9 were used for this and are commonly called the
"cascade" IRQ, as they allow the second PIC to cascade an IRQ down to
the first PIC.

 

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