C191:
Operating Systems
Study Guide
Hardware and User Needs
Memorize and complete the following table from Section 1.1 in Zybooks:
Hardware
Hardware Components
User Needs
Component
CPU
Examples of the
Hardware
Machine instructions perform
The user thinks in
The control Unit,
operations on contents of registers
terms of arrays, lists
Arithmetic Logic Unit,
and memory locations.
and other high-level
registers, Cache
data structures,
accessed and
manipulated by other
high-level operations
Main
Physical memory is a linear
The user must manage
Primary Memory – RAM
Memory
sequence of addressable bytes or
a heterogenous
(Random Access
words that hold programs and data
collection of entities of
Memory, stores the
various types and sizes
data that the CPU
and sizes, including
actively uses during
source and executable
program execution.
programs, library
SRAM, DRAM
functions and
dynamically allocated
data structures, each
accessed by different
operations.
HDD, SSD, Flash drives,
Secondary
Disk and other secondary storage
The user needs to
magnetic tape, memory
Storage
devices are multi-dimensional
access and manipulate
cards
structures, which require complex
programs and data sets
sequences of low-level operations
of various sizes as
to store and access data organized
individual named
in discrete blocks.
entities without any
knowledge of the disk
organization
I/O Device
I/O devices are operated by reading
The user needs simple,
Keyboards, printers,
and writing registers of the device
uniform interfaces to
screens etc.
controllers.
access different devices
without detailed
knowledge of the
access and
communication
protocols.
History of Computers
Memorize and complete the following table from Section 1.3 in Zybooks:
Generation
Generation 1
Enabling Hardware Technology
Vacuum Tubes
OS type
None
Defining Characteristics
All programming was
done by experts in
machine language
without any support
from an OS or any other
system software.
Generation 2
Transistors
Batch
Programs were
submitted in batches of
punch cards. The role
of the OS was to
automate the
compilation, loading
and execution of
programs.
Multiprogramming was
developed, which
allows the OS to
schedule the execution
of jobs to make more
efficient use of the CPU
and other resources.
Generation 3
Integrated circuits allowed the
Multi-programming,
Interrupts were
development of microchips to
multi-tasking
developed to allow the
replace individual transistors
Interactive multi-user
OS to enforce time-
OS
sharing and to interact
with keyboards and
display terminals, also
developed during the
same period. Increased
capacity and speed of
memory and secondary
storage devices
imposed additional
management tasks on
the OS.
Generation 4
Very Large-Scale Integration VLSI
Multi-processor.
The OS was responsible
allowed the placement of a
for all operations,
complete microprocessor on a
starting from the initial
single chip, leading to the
booting, to
development of personal
multitasking,
computers.
scheduling, interactions
with various peripheral
devices and keeping all
information safe. The
emphasis was on userfriendliness, including
the introduction of the
GUI.
Generation 5
Networking hardware enabled the
OS for supercomputers
The ability to create
harnessing of the power of
and mobile devices
extremely powerful
multiple computers.
chips spawned several
directions of
development.
Supercomputers
combined large
numbers of processors
and made the OS and
other software
responsible for
exploiting the
increased computation
power through parallel
processing. Computer
networks gave rise to
the internet, which
imposed requirements
of privacy and safety
along with the efficient
communication.
Wireless networks led
to the development of
hand-held devices with
additional demands on
the OS.
Windows and Linux Commands
Use your book, additional resources, and the internet to memorize and complete the table:
Operation
Definition
Windows
Windows GUI
Linux Command
cd path/directory
Command
(Command
Prompt)
Change
Change the current
cd
Double
working directory to
path\to\director
clicking in fire
another directory
Create
explorer
Create a new named
Mkdir directory
Right click
Mkdir
directory
name
select new
directoryname
folder
Delete
Delete directory from
rd /s
Right click and
rm -r
the path (and deletes
directoryname
delete
directoryName
Move a directory to
move source
Drag, or cut
mv source dest
another
destination
and paste
Rename
Rename a file directory
rename old new
mv oldname new
List
List all the file names
dir
ls -l
all the files and
directories nested
within the deleted
directory)
Move
and other attributes
within a specified file
name
Find
Find a file or directory
Wildcard: *
by name
Locate
Print
Mounting File
System
dir /s /b
Print to screen
echo Text
locate
echo “text”
moutn
Unmounting
File System
Ping
ping
ping <hostname
or ip>
Ipconfig
Display File
Contents
Stream Editor
for Editing
Text
Security Questions
Memorize and complete the following table from Chapter 16 in Zybooks:
Type of
Also
Key for
Key for
Algorithm
Describe the
Cryptography
known
Encryption
Decryption
Used for
Cryptography
as…
(Circle one)
(Circle one)
Encryption
(Circle one)
Symmetric
Secret
/ Private
/ Private
DES /
Key
Symmetric
encryption uses
the same key for
both encryption
and decryption of
data. It relies on
the secrecy of the
single key, which
must be shared
with the user
doing the
decryption.
Asymmetric
public
Public/
/ Private
RSA /
Asymmetric
encryption uses a
pair of keys,
public to send
and private to
receive and
decrypt. Only the
holder of the
private key can
decrypt the data.
It benefits from
not needing to
share keys for
decryption.
What is a man-in-the-middle attack? Attacker secretly listens to and possibly alters communication
between two systems.
What is a logic bomb? Unauthorized code inserted into the system and executed at a specified time to
perform some destructive action.
What is a back door? A mechanism that bypasses user authentication
What is a trapdoor? Similar to a backdoor, A secret entry point that allows unauthorized access to a
system.
What is information leaking? The disclosure of confidential or secret information by a legitimate user
to an unauthorized user.
When someone from inside the organization poses a threat with information, what is that called?
Insider Threat
What is login spoofing? A legitimate user presents a fake login screen to an unsuspecting user who
unwittingly supplies a valid login name and password to the imposter program
How is login spoofing different from phishing? Phishing is not an insider attack
How is login spoofing different from social engineering? Login spoofing is performed by someone who
already has access, social engineering does not necessarily require access and can be performed from
the outside.
What are the differences between a virus and a worm? A virus attaches itself to a legitimate program or
file and spreads by inflecting other files or programs. A worm is a standalone program that doesn’t
require a host program to spread.
What is a trojan horse? A trojan horse is malware that pretends to be a legitimate program and is
downloaded by the user but has hidden functions intended to violate computer security.
What is a buffer overflow attack? An intrusion technique that exploits the fact that many programs do
not check for array overflow, allowing an attacker to overwrite portions of memory beyond the
legitimate scope of an input buffer.
When a bad actor adds code to a form online that exposes customer information later is that a buffer
overflow attack or a logic bomb? Logic Bomb
Why should developers use a sandbox? When testing an known or new software from an known source
or that may produce unknown events. It keeps the user system protected and isolates the tested
program.
What is a hash?
A hash is a value that is generated from a string of text, usually a data input of any length.
What is a DDoS attack? Distributed Denial of Service attack. – An attempt to disrupt the regular
functioning of a targeted server, service or network. The DDoS overwhelms the target with a flood of
internet traffic, usually generated by botnets.
What does defense in depth mean? The theory that more layers of defense provide stronger defense
than fewer layers.
Describe Salting using a picture:
What is Dropbox? A cloud-based file storage and synchronization service that allows users to
store, share and access files and folders across various devices.
What can be used to access Dropbox? Dropbox is accessed via the internet or another WAN
There are three types of factors of authentication: something you have, something you know,
something you are. Describe and provide an example of each:

Something you know: The color of your first car / mother’s maiden name.

Something you are (also known as biometrics): retinal scan, finger / palm scan

Something you have: A keycard, a password,
In cybersecurity, there is a principle of least privilege. Define the following:

Principle of least privilege: A design principle stating that every program and every
privileged user of the system should operate using the least amount of privilege
necessary to complete the job.

Role-Based Access Control (RBAC): Role-Based Access Control – A security model and
access control mechanism used to manage and control access to resources within a
system or application. RBAC assigns permissions to users based on their roles,
making it easier to manage access rights and maintain security.

Roles: Roles are predefined sets of permissions that define what actions or operations
a user is allowed to perform. For example, roles might include administrator, user,
manager, etc.

Discretionary Access Control: Allows the owner of a resource like a file or folder to
control who has access to that resource and what level of access they have.

Mandatory Access Control: Enforces strict control over access to resources based on
predefined security policies and labels. In MAC, access decisions are determined by
the system administrator or security policies rather than the owner.
Access and Capabilities List
For capabilities lists, find the object and work down that column
For access lists, find
the domain and work
across that row
What does * or c mean in an access list? (Hint: you may need to look in the course tips or
announcements) The holder of rc may copy r to another domain.
Memory Questions
What is an example of physical memory and its limitations? A computer’s physical memory is a
hardware structure consisting of a linear sequence of words that hold a program during
execution. It can be damaged and requires physical space to store, it is generally slower.
What is logical memory and why is it used? Logical / virtual memory is a memory management
that is used to provide the illusion of a larger memory space than is physically available. It allows
programs to use more memory than is actually installed.
When memory is considered volatile, what does that mean? Volatile memory is only active while
the system is powered, when the power is turned off the programs in volatile memory disappear.
When memory is considered nonvolatile, what does that mean? Nonvolatile memory retains data
when the power supply is turned off or interrupted. and is used for long term data retention.
What is DMA and when is it used? Direct memory access controller is a hardware controller that
allows devices to access main memory directly, without involvement of the CPU
Paging
Using Chapter 7 in your Zybooks, complete the following table:
Term
Definition
Metaphor
Page Table
An array that keeps
A “phone book” of
track of which
where data resides
pages of a given
logical address
space reside in
which page frames.
Page
A fixed-size
A “page” of a
contiguous block of
phone book
physical memory
identified by a
single number, the
page number
Page Frame
a fixed-size
An “ad” of a phone
contiguous block of
book
physical memory
identified by a
single number, the
page frame
number.
Why do we use a page table? A page table is used to map virtual addresses to their corresponding
physical addresses.
How does a page relate to a logical address space? The logical address space is divided into
fixed-size blocks, these are called pages.
How does a page frame relate to a physical address? A page frame is a fixed-size block of
physical memory, it is equivalent in size to a page in the logical address space.
Define the following: Logical Address, Logical Address Space, and Physical Address.
A logical address is an integer in the range[0:m-1] that identifies a word in the logical address
space.
A logical address space is an abstraction of physical memory, consisting of a sequence of
imaginary memory locations in a range [0:m-1], where the size of m is the size of the logical
address space.
A physical address in an integer in the range[0:n-1] that identifies a word in the physical memory
of size n.
Page Replacement
What is a page replacement and page fault rate?
Page replacement is the act of overwriting a page in memory with a different page loaded from the disk
when needed.
A page fault rate is the number of page faults, f, occurring during a number of memory references, t.
The page fault rate can be expressed as P=f/t,
What is the best page replacement algorithm? The optimal page replacement algorithm selects the
page that will not be referenced for the longest time in the future.
Which page replacement algorithm results in the fewest number of page faults? The optimal page
replacement algorithm.
What is the optimal page replacement algorithm? The optimal page replacement algorithm selects the
page that will not be referenced for the longest time in the future.
What is the FIFO page replacement algorithm? The FIFO page replacement algorithm selects the page
that has been resident in the memory for the longest time.
What is the LRU page replacement algorithm? The least-recently-used page replacement algorithm
selects the page that has not been referenced for the longest time.
What is the Aging Replacement algorithm?
The aging page replacement algorithm does not maintain pages sorted in the exact LRU order, but
groups together pages referenced during a period of d consecutive references. Each period is
represented by 1 bit in a periodically shifting aging register.
Describe the process that occurs in the second chance page replacement algorithm: The r-bit
divides all pages into only two categories, recently referenced and not recently referenced. A page is
then selected from the not-recently referenced category.
Describe the process that occurs in the third chance page replacement algorithm: The NRU (
not-recently-used) algorithm is a coarse-grain approximation of LRU, which divides pages into 4
categories based on the 4 possible combination of the r-bit and the m-bit.
What is the Working Set algorithm? A trailing window of size d is superimposed on the RS to determine
the size and composition of the working set at time t.
What is the Optimal Working Set algorithm? A set of resident pages that will still be needed in the
immediate future and thus should remain resident.
What is the Working Set Page Replacement Algorithm? The most relevant pages of a process are kept in
memory, reducing page faults and improving performance.
What is the Page Fault Frequency Replacement Algorithm? – Adjusts the current resident set based on
how frequently consecutive page faults occur.
What is thrashing? An execution state during which most of the time is spent on moving pages
between the memory and the disk while the CPU is mostly idle and no process is making any real
progress.
Fragmentation
What causes the following types of fragmentation:
Internal: A mismatch between the page size and the size of the program that creates a hole
at the end of the programs last page.
External: The loss of useable memory space due to holes between allocated blocks of
variable sizes.
What is a boot partition? A storage device containing an executable operating system.
Draw a diagram showing the user powering up their computer and initiating the boot partition,
boot sector, boot kernel, and OS:
Power ON -> Master boot record { boot code / partition table}
|
boot partition
|
boot sector
|
boot kernel -> Loaded OS
In the 50% rule, how much of memory is wasted on average? (Circle one):

1/3
Memory Management
Define and draw a picture of memory
Define and draw a picture of memory
swapping:
compaction:
In compaction, The blocks are moved to
make space for the new request.
Segmentation and Segment Tables
What is the difference between a segment table and page table?
Define the following terms using Chapter 8 in your Zybooks:
Term
Definition
Potential ways to
remember it on the exam
Segment
A variable size
block of logical address
Smallest unit of data for
memory management
space identified by a
single number, the
segment number
Segment Table
An array that keeps track
Each entry corresponds to
of which segment resides
one segment and contains
in which area of physical
the starting address of the
memory. Each entry
segment
corresponds to one
segment and contains the
starting address of the
segment.
Address Translation
Address translation in
Like paging within a
segments allows a
segment
program to use a larger
address space while
maintaining efficient
memory management.
TLB
A fast associative memory
Like remembering where
buffer that maintains
the local stores are around
recent translations of
your house without having
logical addresses to
to use GPS to get there
frames in physical
faster. TLB saves the
memory for faster
logical -> physical
retrieval
address translation with
the frame number
Hit Ratio
The fraction of memory
component
If found, easier to get
accesses that find a match
there sooner and less
in the TLB. The higher the
overhead used. (Easier to
TLB hit ration, the lower
get to the store without
the
GPS if you know it by
muscle memory)
Principle of Locality
Locations accessed
We are creatures of habit –
recently are more likely to
if we did something
be accessed again than
before, chances are we are
locations accessed in the
going to do it again soon
distant past.
Types of Memory Fits
Use Chapter 7 in your Zybooks to complete the following table:
Draw a picture and define best fit:
Draw a picture and define worst memory
fit:
Searches the entire list and chooses the
Always chooses the largest available hole for
smallest hole large enough to
any request.
accommodate the request
Draw a picture and define next memory fit:
Draw a picture and define first memory fit
Starts the search at the point of the last
Starts from the beginning of the list and
allocation.
allocates the first hole large enough to
accommodate the request.
Processes and Threads
A program in execution is called: A process
What is a PCB and what is it purpose? A data structure that holds information for a process,
including the current instruction address, the execution stack, the set of resources used by the
process and the program being executed.
How many threads are there to a process? One to many
How many processes are there to a PCB? A single process
What is a program counter? A CPU register indicating the main memory location of the next
instruction to load and execute.
While the acronyms may be similar, PC and PCB are completely different. Describe their impact on
processes and threads: A program counter keeps track of the process that currently has access to
the CPU, the processes control block handles the threads and the completion of the process itself.
File Control and Directory
Define and provide an example of each for the layered file system diagram below:
A program designed for end-user execution. Microsoft Word is meant to be
used by the user and runs on top of the operating system.
A logical layer of the operating system responsible for file and file-system
metadata management, maintains the FCB
File-organization module – A logical later of the operating system responsible
for files and for translation of logical blocks to physical blocks.
basic file system- A logical layer of the operating system responsible for
issuing generic commands to the I/O control layer, such as “read block x” and
also buffering a caching I/O.
I/O control – A logical layer of the operating system responsible for controlling I/O,
consisting of device drivers and interrupt handlers.
Devices are the input and output suppliers, keyboards, printers etc. run by device drivers which
manage their actions with the system.
List 4 things that a file system must be able to do:
1. Store large amounts of data
2. Metadata
3. Control over access
4. Maintain data integrity
Select the correct answers:
1. Where are files stored in UNIX? (Select 1.), UFS,
2. Where are files stored in Windows? (Select 3.) NTFS, FAT or FAT32
3. Where are files stored in Linux? (Select 2.) ext3, ext4,
Reminder: Look at the course announcements and resources for additional information on
NTFS and ext3/ext4 not covered in the textbook, but required for the OA
Define the three ways what a file type can be identified:
1. Magic Number: Short sequence of characters at the start of the file header, which identifies
the file type.
2. File Header: A portion of the file preceding the actual data and is visible only to the FS itself.
3. File Extension: A sequence of one of more characters following the file name.
Why is a file extension the most vulnerable to corruption issues? It can easily be changed
Using the picture below from Windows, square the relative path name and circle the absolute path
name for this folder:
Relative path is This PC > Downloads > Test
Absolute path name is C:\Users\chris\Downloads\Test
Define the following terms:
File Directory or Folder: A special purpose file that records information about other files and
possibly other directories.
Root: The highest level directory, which does not have a parent directory.
Relative Path Name: A concatenation of file names starting with the current directory.
Absolute Path Name: The full path name of the file, leading down to the file root
Draw a Picture
Directed Acyclic Directory
Symbolic Link Directory
Structure
Structure
Define the Term
Directories organized such
Symbolic links point to a file
that any directory at a given
or directory like a regular
level may point to zero or
entry but are treated
more files or other
differently with respect to
directories at lower levels
deletion. Deletion removes
but also permits any file or
the link but not the original
directory to have more than
file.
one parent directory.
What does FCB stand for? File control block
Describe the following picture from Zybooks and why approach 3 is used within the file control
block: The critical attributes are kept in the directory. All other attributes are kept in file control
blocks. This prevents the directory from getting too large.
Define PCB: Process control block, a data structure that holds information for a process, including
the current instruction address, the execution stack, the set of resources used by the process and
the program being executed.
Define FCB: File Control Block – A data structure associated with a filename that contains all
relevant attributes of the file. FCBs are stored apart from file directories and are pointed to by the
corresponding directory entries.
Identify if the following pictures are either Contiguous, Clustered, or Linked and define the term:
Contiguous – Every file is mapped into a contiguous sequence of disk blocks.
Linked – blocks containing a file may be scattered throughout the disk. The FCB points to the first
block and each points to the logically next block.
Clustered – The last block of any clucster points to the beginning of the logically next cluster.
Operation
Describe what happens with the file and FCB
Create File
Causes the creation of a new named file, the FS allocates and initializes a
new FCB.
Destroy File
Removes an existing file from the FS. Reversed the process of creation
freeing up the files FCB and directory entry.
Open File
A data structure that keeps track of all files currently in use to facilitate
Table
efficient access to and manipulation of the files.
Open File
Prepares a file for efficient access and manipulation by retrieving relevant
file information from the FCB and storing the information in an entry of the
OFT.
Read File
Copies data from an open file to a specified area in main memory.
Write
Copies data from an area in main memory to a specified open file.
Seek
Moves the current position of an open file to a new specified position.
Which accounts can destroy a file? The owner
How does Windows present a common interface for all system calls to avoid complex per-program
coding? The windows GUI, represented as digital clickable files on the interface.
Memory Management
Complete the following table by filling in the blanks of either the term or definition:
Term
Definition
Raw
No file system is used. Can be used for a
Unix Swap Space
Cooked disk
A disk that contains a file systems
Bootstrap loader (boot loader)
Stored in firmware, finds the kernel (by
knowing the file system) and starts
executing it when the system is powered on
Boot control block (per volume)
Contains information needed by the system
to boot an operating system from that
volume. If the disk does not contain an
operating system, this block can be empty.
Partition Boot Sector
What the boot block is called in NTFS
Volume control block
Contains volume details (number of blocks,
size of blocks, and free block pointers)
What is mounting? Making a file system available to the operating system and users, when
mounted, a file system becomes accessible.
What are the steps for mounting a table?
I can’t find this ?
Step 1: Specify source and target
Step 2: Issue the mount command
Step 3: Access the mounted file system
What is mount used for within the Linux operating system?
It us used for attaching file systems to the existing file system hierarchy.
What is memory mapping? Mapping a disk block to a page or pages in memory. The
What is memory-mapped I/O? A shared memory used two or more different processes.
I/O
Term
Port
Definition
A communication address, each fo
separate communication. A connection point
for devices to attach to computers
Bus
A communication system within a computer,
connecting varius components such as the
CPU and I/O devices, allowing them to
transfer data and commands.
Daisy Chain
A connection method involving connecting
devices to each other in a string.
Device Driver
A device-specific program that implements
I/O operations, requested by user
applications or the OS, by interacting with
the device controller.
Device Controller
An electronic circuit capable of operating
specific I/O devices using binary signals.
Which is a piece of hardware: device controller
Which interacts with the operating system and translates information from the I/O device into
genetic system call? Device Driver
Which storage device is directly connected via a serial bus? Serial ATA hard drives and solid state
drives
Which two are directly connected to a computer? (Select 2.) Host-attached, Cloud Storage
Polling vs. Interrupts
Which system call method is like asking “…are we there yet?...” because it is repeatedly checking to
see if the /O device is available or busy waiting? Polling
Which system call method only announces itself once it has arrived? Interrupt
Describe how interrupts work with the interrupt request line and what ‘maskable’ means. The
interrupt-request line is a hardware connection to the CPI on which interrupts are signaled. The
CPU senses it after executing every instruction. When a controller has asserted a signal on the
interrupt-request line, the CPU performs a state save and jumps to the interrupt-handler routine.
Disk Scheduling
Fill in the following diagram with the following words: Track, Sector, Cylinder, Shaft. Each word
may be used more than once.
Fill in the terms within the following table:
Term
Definition
track
One or many concentric rings on a magnetic disk surface
sector
Smallest portion of a track that can be read or written to via a
single r/w operation. Each sector r/w data in blocks.
seek time

Proportional to the distance traveled

Time to move the r/w from the current position to the
track containing the right data
1

Proportional to 2disk revolution

Time to wait for the desired sector/data item to pass under
the r/w head
transfer rate

Proportional to the disk’s speed

Time to transfer the desired bits to/from the disk
Also transfer rate? There
Data streamed to or from the disk once the head is at the
is no specific question
beginning of the sector to be transferred
that I can find like this.
transfer rate
The rate at which the data can transfer continuously
head crash
R/W head collides with the platter and causes damage
rotational latency?

Speed changes because the outer edges of the track hold
40% more sectors than the inner tracks

Maintains transfer rate and density per track

Maintains speed

Changes transfer rate
Disk Access Optimization
Assume that the R/W head is at track 50 and needs to go to the following tracks (in no particular
order): 0, 10, 55, 70, 100, and 105.
Draw what it would look like under the shortest seek time algorithm:
Define the shortest seek time algorithm: 55, 70, 10, 0 100. 105
Draw what it would look like under the C-Scan algorithm:
Define the C-Scan algorithm: 55, 70 100, 105, 0, 10
Draw what it would look like under the Scan algorithm: 10, 0, 55, 70, 100, 105
Define the Scan algorithm: The r/w head maintains a current direction of travel and services all
requests sequentially in the current direction. When the outermost request is reached, the
direction is reversed and the algorithm services all requests in the opposite direction.