Skip to main content

Logical and physical address bits

Short answer

A resident monitor is the earliest OS form that stays permanently in memory to sequence jobs automatically. Logical address: 13 bits (3 page + 10 offset). Physical address: 15 bits (5 frame + 10 offset).

What is residence monitor? Consider logical address spaces of eight pages of 1024 words, each mapped onto a physical memory of 32 frames then. a) How many bits are in logical address? b) How many bits are in physical address?

Resident monitor

The resident monitor is the earliest form of an operating system, used in batch systems. It is the small part of the OS that stays permanently ("resides") in main memory and automatically sequences jobs so that the CPU does not wait for an operator between jobs. Its parts:

  • Control-card interpreter: reads and executes the control cards (e.g. $JOB, $LOAD, $RUN, $END) that tell it what to do.
  • Loader: loads a user program into memory.
  • Device drivers: handle the I/O devices used by the system and the user program.

Memory is divided into the monitor area and the user-program area; hardware (a boundary register) protects the monitor. When one job ends, control returns to the monitor, which loads the next job.

 +----------------+
 | Resident       |  always in memory
 | monitor        |
 +----------------+  <- boundary
 | User program   |
 | area           |
 +----------------+

a) Bits in logical address

  • Logical address space = 8 pages × 1024 words = 8192 words = 2¹³ words.
  • Page number needs 3 bits (8 = 2³), offset needs 10 bits (1024 = 2¹⁰).
  • Logical address = 3 + 10 = 13 bits.

b) Bits in physical address

  • Physical memory = 32 frames × 1024 words = 32768 words = 2¹⁵ words.
  • Frame number needs 5 bits (32 = 2⁵), offset 10 bits.
  • Physical address = 5 + 10 = 15 bits.

Answer: logical address = 13 bits; physical address = 15 bits.

✓ Answer checked by Claude Opus 5.5 (high effort)

Related questions

All Operating System chapter 4 questions →