Virtual Memory

Question 1

In order to manage memory more efficiently and with fewer errors, modern systems provide an abstraction of main memory called ——- ——.

Also known as process of indirection

Answer 1

Virtual Memory (VM)

Question 2

What is the purpose of Virtual Memory

Answer 2

1. Solves the problem when we don’t have enough memory space (RAM)
2. Be able to fill holes in memory space
3. Keep program secure and data corruption

Question 3

What is “address translation”?

Answer 3

With VM addressing, the CPU accesses main memory by generating a “virtual address” (VA), which is converted to the appropriate “physical address” (PA) before being sent to main memory.

The task of converting a “virtual address” (VA) to a physical one is known as “address translation”

Question 4

What is the MMU (memory management unit) for?

Answer 4

Dedicated hardware on the CPU chip called “MMU” translates “virtual addresses” on the fly, using a lookup table stored in “main memory” whose contents are managed by the OS or operating system.

In other words, MMU is a hardware on the CPU chip which translates a “virtual address” (VA) to “physical address” (PA) to retrieve a requested memory address to get the data.

Question 5

What is the difference between the virtual address space and physical address space?

Answer 5

In the Virtual Memory (VM) system, the CPU generates virtual addresses from an address space of N = 2^n addresses called the “virtual address space”

For example, a VMA (virtual address space) with N = 2^n address is called an n-bit address space.
Typically, 32-bit or 64-bit address space. Which means for a 32-bit address space, the number of Virtual addresses (N) it can generate is 2^32 or 4 Gigabytes worth of VMA with the largest possible virtual address of (4G-1) or (2^32 - 1)

PAS (physical address space) corresponds to the M bytes of physical memory in the system. Usually what the capacity of RAM. Assumed M = 2^m bit where m-bit determines the size of an address space needed to represent the largest address.

For example, 4 KBytes of Ram is equal to 2^12 which means the system has a 12-bit address promised by its physical memory.