Difference between ARM7 and intel i3, i5 & i7 processors
ARM7 has 21 external interrupt pins

No, a generic ARM7 has two external interrupts: IRQ and FIQ.
The problem here is &quot;architecture&quot; versus &quot;implementation&quot;. ARM7 is an architecture. LPC2148 (for example) is an implementation of that architecture. The implementation has pins, cache, etc. You got that information from this page, perhaps?
Intel handle interrupts very differently. A datasheet for Intel. It has no external interrupt pins - instead it has a PCI-E bus, and messages on that bus can be translated into interrupts.