Question

Galvin says:

We may place operating system in either low memory or high memory. The major factor affecting this decision is the location of interrupt vector. Since the interrupt vector is usually in low memory, programmers usually place operating system in low memory as well.

I am not quite sure as how the location of interrupt vector affects the location of OS in memory. I tried to google but could not find anything to my satisfaction.
Can someone please clarify this.

Answer 1

The main memory has primary 2 parts:

1. Resident OS with low memory with interrupt vector, where “An interrupt vector is the memory address of an interrupt handler”, i.e. it’s one of the lowest levels of memory.
2. User processes in high memory

Now, why is the OS held in low memory?
As you go no high up in the memory, the cost per byte increases and since the OS needs quick access to memory, it should be places lowest in the order.

So, the location of interrupt vector is not the direct reason for operating system to be placed, but it’s the the low memory requirement. We know, interrupt vectors will be placed there, so OS is also placed with it.