13 - Address Spaces

Question 1

What is the VM system responsible for?

Answer 1

providing the illusion of a large, sparse, private address to each running program

Question 2

What does each virtual address space contain?

Answer 2

All of a program’s instructions and data

Question 3

What does the OS do with each virtual memory reference?

Answer 3

Turn them to physical addresses

Question 3

What is presented to the physical memory in order to fetch or update the desired information?

Answer 3

Physical addresses

Question 4

What is multiprogramming?

Answer 4

multiple processes are ready to run at a given time, and the OS can switch between them.

Question 5

Name a benefit of multiprogramming.

Answer 5

increased effective CPU utilization which lead to increase efficiency

Question 6

Name optimal way to implement time sharing

Answer 6

leave processes in memory while switching between them, allowing the OS to implement time sharing efficiently

Question 7

Name something about protection

Talk about what you want or don’t want a process to do

Answer 7

You don’t want a process to be able to read or write some other process’s memory

Question 8

The easy to use abstraction of physical memory is also known as?

Answer 8

Address space

Question 9

What is the running program’s view of memory in the system?

Answer 9

Address space

Question 10

What is the ‘code’ of the program otherwise known as, and where is it?

Answer 10

the instructions of the program and they are in the address space

Question 11

What data structure does the running program use and for what? (First one mentioned)

Answer 11

A stack. Keep track of where it is in the function call chain as well as to allocate local variables and pass parameters and return values to and from routines

Question 12

What data structure does the running program use and for what? (Second one mentioned)

Answer 12

A heap. for dynamically-allocated, user-managed memory

Question 13

What are three components in an address space?

Answer 13

code, stack, heap

Question 14

Is code static or dynamic, and what are the perks of it?

Answer 14

Static. Easy to place in memory and can place it at the top of the address space and know that it won’t need any more space as the program runs.

Question 15

Are stack and heap dynamic or static and where are their locations, respective to each other?

Answer 15

Both are dynamic. Heap is above stack. Stack is below heap.

Question 16

What about heap and stack’s growth?

Answer 16

They have to grow in opposite directions. Heap grows downward while stack grows upward.

Question 17

Can stack and heap be placed differently?

Answer 17

Yes, when multiple threads co-exist in an address space, dividing the regions nicely like this won’t work anymore

Question 18

When processes are loaded into memory at different addresses, what is the OS doing?

Answer 18

Virtualizing memory. The running program thinks it is loaded into memory at a particular address and has a potentially large address space. The reality is different.

Question 19

What if a process tries to perform a load at a virtual address?

Answer 19

Somehow the OS, along with hardware support, will have to make sure the load doesn’t actually go to the physical version of the virtual address but rather the physical address of where the process is loaded into memory.

Question 20

What are the three goals of virtual memory?

Answer 20

Transparency, Efficiency, Protection

Question 21

In Transparency, how does the OS implement virtual memory and how should the program behave?

Answer 21

In a way that is invisible to the running program. The program should behave as if has its own private physical memory.

Question 22

In Efficiency, on what terms should the virtualization make as efficient as possible and what will the OS rely on?

Answer 22

time(not making programs run more slowly) and space(not using too much memory for structures needed to support virtualization). The OS will have to rely on hardware support, like TLBs

Question 23

In Protection, what should the OS makes sure to do and what property does the OS deliver to each process?

Answer 23

The OS makes sure to protect processes from each other and the OS itself from the processes. When a process is in action, it should not be able to access or affect in any way the memory contents of any other process or the OS itself. The OS delivers ISOLATION among processes.

Question 24

What is a key principle of building reliable systems?

Answer 24

Isolation

Question 25

What kernels are used in Isolation?

Answer 25

Microkernels