text: Q:
  
  Why is the OS held in low memory?
  
  Peter B. Galvin says that the major factor affecting this decision is the location of the interrupt vector. Since the interrupt vector is usually in low memory, programmers usually place operating system in low memory as well. I really don't understand why the OS has to be next to the interrupt vector.
  
  A:
  
  It sounds like you are in the midst of textbook BS. To begin, you are only talking about parts of the operating system that have physical locations. The rest of the kernel will be in virtual/logical locations.
  The interrupt vector is going to be one part of the kernel that has been in physical memory. On most systems you can put the interrupt vector anywhere in memory.
  The interrupt vector is part of the operating system. It would make sense to allocate physical memory for the operating system in a contiguous block (ignoring physical memory locations used by devices). Thus, the interrupt vector is likely to be in the same block of reserved physical memory as the rest of the OS uses. The interrupt vector COULD be all alone and separated from the rest of memory used by the operating system but it is easier to do it all in one.
  So you're writing your operating system. Where are you going to put this block of reserved memory?
  Intuitively, people are going to select either the high end of low end of physical memory.
  
  