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GO Classes DPP | GATE CS | Operating System | Base-Bound Accesses

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2 2 votes

A system uses base-and-bound address translation.

The registers contain:

$\texttt{base} = 1000$

$\texttt{bound} = 100$

The CPU fetches and executes the following instruction:

$\texttt{load 10, r1}$

Assume that the instruction itself is stored at a valid logical address.

How many main-memory accesses are generated while fetching and executing this instruction?

  1. $0$
     
  2. $1$
     
  3. $2$
     
  4. $3$

1 Answer

1 1 vote

The instruction requires two separate main-memory accesses.

First memory access: The CPU fetches the instruction $\texttt{load 10, r1}$ from memory.

Second memory access: The CPU loads the data stored at logical address $10$.

The physical address of the operand is:

$\text{Physical address} = \texttt{base} + \text{logical address}$

$= 1000 + 10$

$= 1010$

The bound check and address addition are performed by hardware. 

They do not require an additional main-memory access.

$\therefore\text{Total memory accesses} = 1 + 1 = 2$

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