Midterm Review 1-25

Question 1

What are the five main categories of modern computer systems?

Answer 1

Personal Mobile Device (PMD)
Desktop Computing
Servers
Clusters / Warehouse Scale Computers
Embedded Computers

Question 2

What is the primary task of an operating system?

Answer 2

Answer 1: A program that acts as an intermediary between a user of a computer and the computer hardware.

Answer 2: OS is a resource allocator, which manages all resources, decides between conflicting requests for efficient and fair resource use, and controls programs within allocated space.

Question 3

What are the two main characteristics of an OS?

Answer 3

Efficiency and convenience.

Efficiency means that the OS can manage multiple processes and allocate memory to these processes fairly and efficiently. For example, if one process is trying to hug a large number of frames, the other processes should not be denied active frames. If a process is not using its frame or CPU assets, that process should be deactivated. In servers, efficiency is of main importance.

Convenience is a factor that a user of the system expects from the OS. Allowing a user to access programs and applications easily is an example. In mobile devices, convenience is a major factor.

Question 4

For networked distributed computing, the networks are categorized into four groups in terms of the distance between members. What are these four types of networks?

Answer 4

LAN: local area
WAN: wide area
MAN: metropolitan area
PAN: personal area

Question 5

Computing environments, in terms of the role of connected members of a network, are divided into two types. What are these two types of networks?

Answer 5

Client-server

Peer-to-peer

Question 6

What is the difference between “emulation” and “virtualization?”

Answer 6

Emulation is used when the source CPU type (physically present) is different from the target CPU type (the CPU that a program is compiled for). For example, Apple desktops switched from IBM CPU to Intel CPU, and old software used Rosetta to run on emulated IBM CPU.

Virtualization allows a guest OS to run as an application on a host OS.

Question 7

What is the difference between “full virtualization” and “para-virtualization?”

Answer 7

In full virtualization, the guest is an original OS and wants to manage the memory, perform protection, etc. In para-virtualization, guest OS is designed to run as a guest in a virtual environment and is aware of other operating systems, and knows its limitations.

Question 8

What are the three types of “cloud computing?”

Answer 8

Private, public, hybrid

Question 9

What are the three advantages of a “multiprocessor system” over a single processor?

Answer 9

1- Increased throughput
2- Lower cost than using a collection of single processors
3- Reliability is higher, and the system is more fault-tolerant

Question 10

What is the difference between “symmetric” and “asymmetric” multiprocessors?

Answer 10

Asymmetric multiprocessor is a CPU scheduling method in which all scheduling decisions, I/O processing, and other system activities are handled by a single processor — the master server. The other processors execute only user code. This is a simple method because only one core accesses the system data structures, reducing the need for data sharing. The downfall of this approach is that the master server becomes a potential bottleneck where overall system performance may be reduced.
Symmetric multiprocessor (SMT) is the standard approach for supporting multiprocessors where each processor is self-scheduling.

Question 11

What are the five activities of “process management?”

Answer 11

1- Creating and deleting both user and system processes
2- Suspending and resuming processes
3- Providing mechanisms for process synchronization
4 -Providing mechanisms for process communication
5- Providing mechanisms for deadlock handling

Question 12

What is the difference between “program” and “process”?

Answer 12

A program is a collection of instructions and is a passive entity. A process is a program in execution and is an active entity.

Question 13

Draw Von Neumann’s architecture of a computer.

Answer 13

sketch!

Question 14

What is a memory unit exposed to?

Answer 14

1- A stream of addresses + read requests

2- A stream of addresses + data and write requests

Question 15

How long does one memory access take?

Answer 15

It takes many CPU cycles.

AMAT= cache-hit-time+ miss-rate*miss-penalty

Question 16

How long does one register access take?

Answer 16

One clock cycle (or less)

Question 17

What do we mean by “throughput of memory”?

Answer 17

Number of bytes accessed in a time unit (Bytes/sec)

Question 18

What does “memory management” mean?

Answer 18

A system that determines what is in memory and when. It is a system that optimizes the CPU’s utilization and the overall computer’s response to users.

(this question says what MM has to do, but we don’t say how it will be done)

Question 19

What does memory management do?

Answer 19

This is how MM should implement its goal: It keeps track of which parts of the memory are currently being used. It means there is, for example, a table showing which frames are occupied by what pages. It decides which processes (or parts thereof) and data to move into and out of the memory. It means that the table has a column for the process IDs showing what pages each process owns. It allocates and deallocates the memory space as needed. It means that the table should be updated as the processes come in or go out.

Question 20

What is meant by the performance difference between DRAM and CPU?

Answer 20

The throughput of DRAM is much smaller than what the CPU requires.

Question 21

What is “memory hierarchy”?

Answer 21

Creating a pyramid with slow, cheap, and large memory at the bottom and placing fast, expensive, and small memories at the top of the pyramid.

Question 22

What is “locality of reference”?

Answer 22

When a reference is made to memory, the same location, or locations near that, will be referenced soon.

Question 23

How could we overcome the performance difference?

Answer 23

By using memory hierarchy.

Question 24

What is the effect of “low” locality of reference?

Answer 24

Low locality causes a high miss rate which forces the memory management to refer to slower parts of the hierarchy.

Question 25

Suppose reading one word from the main memory takes 50 clocks, and reading one block of words from memory would take 100 clocks. Also, assume that reading one word from cache would take 2clocks. What should be the maximum cache “miss rate” for this memory system to worth having the cache rather than directly accessing the main memory?

Answer 25

50>2+miss_rate*100. miss_rate<0.48