Chapter 3 Computer Software

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Chapter 3 Computer Software

• ---- Operating System

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Chapter 3 Computer Software

• Readings
• 3.1 Software Structure
• 3.2 Device Management and Configuration
• 3.3 Resource Sharing
• 3.4 File Systems
• Assessments
• Exercise 3

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  ?????
• ?????????????????????????????????????????
• ???????WINDOWS????? Windows 98? Windows 2000?
  Windows xp?
• - OS????,??

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3.1 Software Structure

• 3.1.1 Layers of Software
• Layers and Process Management
• Software systems are composed of multiple layers
• One example sign a credit card slip to pay for
  dinner at a restaurant a meal
• the meal was actually composed of several
  courses. That is a layer of detail the waiter
  needs to keep track of in order to know what
  dishes to bring, and in what order. For instance
  the first course was salad.

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• The details of salad preparation were handled by
  another layer, the kitchen
• where do croutons actually come from?
• Where do flour come from?
• Where do wheat come from?
• When you pay for your dinner, you are paying
  (indirectly) about one thousandth of a cent to
  that farmer for the wheat in your croutons. And,
  you are paying several thousand other people who
  contributed to your meal in various ways.

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• Fortunately, you do not have to pay all those
  people directly! You make one payment for "a
  meal," and the details are sorted out in the
  layers below.
• By organizing the production process into layers
  that are relatively independent, the entire
  system can be kept manageable, and great
  efficiencies can be achieved. In computer
  science, the principles underlying these benefits
  are called encapsulation and abstraction.

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• Encapsulation and Abstraction (?????)
• Encapsulation means that each layer needs only a
  limited amount of knowledge to do its job, and
  none of the other layers has access to that
  information. The farmer does not know what the
  wheat will be used for. The bakery does not know
  how the wheat was harvested.

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• In the software world, encapsulation means that
  your word processing program does not need to
  know how to control disk drives in order to be
  able to open and save files there are layers of
  software below it that handle those details.
• if a layer were fully encapsulated it would be
  unable to communicate with the layers above and
  below. In order for there to be some exchange of
  information, but not too much, the designer of a
  layer specifies an abstraction that the layer
  promises to support. (??????????)

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• The bakery supports an abstraction called a
  "crouton order," whereby a customer can submit an
  order for X pounds of croutons and the bakery
  will respond by producing the croutons and
  delivering them. The details of how crouton is
  produced are hidden from the customer.
• in computer science terminology(??) we say the
  information is encapsulated

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abstraction

• even if a customer knew that there were two
  ovens(??) to produce the croutons, they could not
  specify(??) which oven they wanted to be used to
  produce their order, because there is no place on
  the order form to indicate that. In computer
  science terms, we say that the crouton ordering
  abstraction does not support oven choice.

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• The existence of well-defined abstractions at
  each layer means that one implementation can be
  replaced by another with no effect on the layers
  above and below.
• On your computer, it is possible to have multiple
  implementations of a software component and
  switch from one to another.

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• For example, your Web browser calls on a helper
  program when it needs to play a sound file or
  video clip. There are several programs that can
  perform this function. All you have to do is tell
  your browser which player to use. This isolation
  of functionality means that if a new, improved
  player becomes available, you can switch to that
  one you do not have to get a completely new
  browser.

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• Layers of Software

• Hardware ,is the lowest level of the computer
  the physical components from which it is
  constructed. Details have discussed in unit 2.

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• The BIOS( Basic Input/Output System), is the most
  fundamental level of software. It deals directly
  with the signals that control each hardware
  component. Much of its work is performed when the
  computer is first turned on.
• Device drivers are the helper programs the
  operating system uses to communicate with a
  specific model of device. The advantage the
  operating system vendor does not have to be
  responsible for supporting every device ever
  invented, or that might be invented in the
  future.

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• Device drivers example The device driver for a
  hard drive knows how many tracks are on the drive
  and what commands to send to the drive to move
  the arm to a specific track and then read or
  write data.
• The device manufacturer supplies the driver, and
  as long as the driver follows the established
  conventions for communicating with the operating
  system, the device should be usable.

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• The kernel is the heart of the operating system
  and performs the functions that are most
  crucial(????) for keeping everything running. It
  manages memory, decides which task to run next,
  and handles the various types of interrupts(??)
  that can occur. The kernel must stay resident in
  RAM at all times, and because of its special
  nature, it must run without some of the
  protection mechanisms that guard against faulty
  instructions or illegal memory accesses.
  Therefore, it is kept as small as possible.

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• The remaining layer of the operating system is
  much larger than the kernel. It implements all
  the other functions the operating system is
  expected to perform. Example file system -
  managing the folders and files on a disk. It
  communicates with the kernel when it needs to
  perform basic actions, such as initiating a data
  transfer operation to a peripheral.

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API

• The application program interface (API), is the
  layer where user programs (applications)
  communicate with the operating system. (API call
  )

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API

• Example suppose a Web browser application
  decides it needs more memory in order to display
  a large image file. The OS is responsible for
  keeping track of which programs are using which
  chunks of memory at any given time. This
  information is encapsulated within the OS the
  application does not know anything about how the
  information is organized. It does not have to.
  The OS defines an abstraction for managing memory
  (API call). All the application developer has to
  know is which API call to use to ask for more. If
  a new version of the OS comes along that uses a
  different way to keep track of memory, the
  application program will continue to work just
  fine as long as the API call stays the same.

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• Run-time libraries are collections of software
  routines that application programs rely on.
• Example you write an application in the C
  language to open a file and read some data from
  it, you will use two built-in functions called
  fopen and fscanf. These functions are fetched
  from a library of I/O routines called stdio that
  can be used by any C program. They will make the
  appropriate API calls to get the OS to do what
  you need. The nice thing about the stdio
  abstraction is that your program is not dependent
  on a specific set of API calls, so you can run it
  on any machine that has a C compiler and an
  implementation of the C runtime library.

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• The application layer is where you will find the
  routines that do the actual work the application
  was created for.
• The user interface layer is responsible for
  communication between the application and the
  user. It is typically a GUI (graphical user
  interface) composed of buttons and pull-down
  menus.
• Scripts or macros are routines that many
  applications allow users to create from the
  application's set of built-in commands. Scripts
  and macros allow users to automate sequences of
  actions they perform frequently.

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• The computer industry today relies on specialists
  in each of the levels listed above. Some people
  make their living writing BIOS software, while
  others concentrate on improving GUI technology.
  But, the greatest number of programmers is found
  at the application level, because people want to
  use computers for so many different tasks.

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3.1 Software Structure

• 3.1.2 The BIOS Life at the Bottom
• The Role of the BIOS
• the lowest level of software on the machine
• it initializes the hardware when the computer is
  first turned on
• it loads the operating system
• it provides basic support for devices such as the
  keyboard, mouse, and serial ports
• it is only visible when you first power on the
  computer, before the operating system takes
  control

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• The BIOS resides in a ROM chip on the
  motherboard. During the power-on sequence, the
  processor automatically starts executing
  instructions from the ROM. Since ROM is slower
  than RAM, the BIOS on most systems immediately
  copies itself from ROM into RAM. Then it tells
  the processor to fetch all further instructions
  from the RAM version.

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• Another special type of memory used by the BIOS
  is CMOS memory. A small amount of CMOS memory,
  often as little as 64 bytes, is included on the
  motherboard to store BIOS parameter settings that
  control the operation of the hardware, and it
  uses very little power.
• If you purchase faster DRAM chips for your main
  memory, you can change the BIOS settings to tell
  the memory bus controller to take advantage of
  the higher DRAM speed.

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POST

• When power is applied to the system and the BIOS
  begins to execute, the BIOS initiates the POST
  (Power-On Self Test) sequence
• First, it enables the video card (you will see
  the screen flash) and displays some basic
  information like the type of video card
  installed, the name of the BIOS manufacturer, and
  the BIOS version number
• It then determines the amount of DRAM installed
  in the system, and it may perform a memory test.

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POST

• Then, after determining what expansion cards and
  adapters(???) are present, the BIOS initializes
  those cards and adapters.
• At the conclusion of the POST sequence, the BIOS
  displays system configuration information, such
  as the type of processor installed, cache memory
  information, the types of each of the disk drives
  it found, the addresses of any serial and
  parallel ports, and a list of other expansion
  cards it detected.

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• After POST, BIOS is to load the OS. the BIOS has
  to know just enough about disk drives to be able
  to read in one chunk of data, called the Master
  Boot Record, or MBR. By convention, this is the
  first sector of the first track of the disk. The
  MBR program then loads in the OS and starts it
  running.
• On a system with multiple disk drives, the BIOS
  follows a search order to find an operating
  system to load.

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• Changing BIOS Settings
• To change BIOS settings, you must enter the BIOS
  setup program during the boot sequence, by
  pressing a specified key or key combination, such
  as F2 or ALTCTRLESC or Del.

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3.1 Software Structure

• 3.1.3 Process(??) Control
• One job of the OS is to keep track of all the
  processes that are currently trying to execute,
  assuring that each gets a chance to execute
  reasonably often.
• A process is an instance of a running program. It
  includes a set of memory pages, a set of open
  file descriptors (if the process does any I/O), a
  process ID, and several other things.

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• Each process can be in one of several states
  running, runnable, or blocked. Only one process
  per CPU can actually be running at a time,
  although any number can be runnable
• The kernel maintains a list of every process in
  the system. And maintains a queue (also called
  the run queue), or waiting list of runnable
  processes .
• Using the Windows NT/2000/XP Task Manager, you
  can examine processes that are running, the
  number of threads a process has, system
  performance, and page faults.

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3.2 Device Management and Configuration

• Another one of the operating system's functions
  is to manage the various I/O devices installed on
  the computer. Control of the hardware at this
  level requires interaction between the kernel,
  the device drivers, and the BIOS.

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3.2.1 Interrupt Handling

• One of the important jobs of the kernel is to
  handle interrupts.
• An interrupt is a signal to the processor that
  some event has occurred that requires immediate
  attention.
• The kernel figures out what caused the interrupt
  and makes an appropriate response. It must act
  very quickly. In order to avoid losing
  information when the next interrupt arrives, it
  must handle each interrupt in less than a
  thousandth of a second.

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• IRQ
• Interrupt Priority and Nested Interrupts Traps
  and Faults
• A trap is an event similar to an interrupt,
  except that instead of being triggered(??) by an
  external signal, traps are triggered by the
  execution of processor instructions. An example
  is a division-by-zero operation.
• A third type of event you should know about is
  called a fault. A fault occurs when the hardware
  is asked to do something it cannot do, such as
  access a nonexistent memory location.

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• 3.2.2 Hardware Attributes
• Installing Drivers
• Each device must have a corresponding driver in
  the operating system. Each operating system
  specifies an interface that a device driver must
  utilize.
• This means that for any particular device, it
  must have a corresponding driver for the
  operating system where it is intended to be used
  in order to be functional.
• Drivers are supplied either with the operating
  system's distribution files, or individually from
  the manufacturer of the hardware device.

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• Changing a Driver's Configuration
• A driver is designed to operate in a particular
  fashion, but it may also include a number of
  operations to customize its functions for a
  particular user or system environment.
• Features to be modified include those that match
  some particular hardware or system requirement
  (such as the transfer speed of a modem, how much
  data to buffer, what protocols should be used,
  etc.), and those that are user-oriented (screen's
  resolution???, wallpaper, a left-handed mouse,
  etc.).

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• 3.2.3 Lab 3-B Using the Windows Interface
• How to access some of the Windows device
  management capabilities
• My Computer - Properties
• 3.2.4 Lab 3-D Installing and uninstalling
  software

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3.3 Resource Sharing

• the OSs mechanism for resource sharing.
• The computer system not only shares many of its
  internal resources, such as the processor, but
  also its external resources, such as the hard
  disk drive.

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3.3.1 Virtual Memory

• Managing Memory
• Some of main memory is reserved for the operating
  system, but most of it is available for user
  programs.
• Each of users programs (running a Web browser,
  an editor, and a computer game etc.) needs a
  certain amount of memory, but none of them needs
  access to all the memory. The kernel allocates
  some memory to each program and keeps track of
  what program is using what.

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• Modern operating systems such as Linux and
  Windows provide virtual memory, to increase
  program flexibility.
• In older operating systems like MS-DOS worked,
  all programs ran in the same real address space,
  since there was no virtual address space
• you (or the compiler) must calculate the address
  for every instruction and every piece of data.
• suppose everyone else writes their programs the
  same way, so you cannot run two programs that
  occupy the same memory addresses at the same time
  since as soon as you load the second one, it will
  overwrite the first.

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• This scheme allows the computer to load multiple
  programs in memory at once, in whatever portion
  of memory is available at the time.
• it is simple to implement and does not require
  any changes to the hardware.
• the memory allocated to the program must be
  contiguous(???)
• Suppose the user is running a half a dozen small
  programs at the same time. After some of these
  programs have exited, programs 1, 3, and 6 are
  left running. Now the user wants to run a big
  application, but unfortunately, there may now be
  nowhere to put it, even though the total number
  of noncontiguous free blocks of memory may be
  more than adequate.

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• the size of a running program is limited to the
  amount of physical memory installed on the
  machine, minus whatever the operating system has
  reserved for itself.
• But, large programs do not normally use all their
  memory at once. A program with a large address
  space may only need to access a few thousand
  instructions and a few thousand bytes of data at
  a time. It would be more efficient to allocate
  only a little bit of RAM at a time to such a
  program and to keep the rest of its address space
  somewhere else, such as on disk. This is what
  virtual memory allows us to do.

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• Virtual Memory
• In a virtual memory system, every program runs in
  its own private address space.
• There is no need for any relocation when the
  program is loaded into memory.
• A virtual address space can be larger or smaller
  than the processor's physical memory.
• virtual memory requires hardware support.

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3.3.2 File and Printer Sharing

• Files and printers are resources of the computer
  that are shared in a networking environment,
  allowing many users to access one drive, file, or
  printer remotely.
• Files may be shared between applications or need
  to be kept private
• the operating system defines a set of permissions
  for a file or directory, also called Access
  Control Lists (ACLs),
• Read access , Write access , Execute access

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3.4 File Systems

• A file system is an abstraction for organizing
  data on mass storage media such as hard drives,
  floppy disks, and optical disks. The file systems
  are managed by the operating system of a
  computer.

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Drives

• Folders are housed in the computer drive.
• One way to access the drives is by
  double-clicking on the icon named "My Computer"
  on your Desktop. you will see that each drive is
  labeled by an icon that indicates the type of
  medium the drive uses. Clicking a drive's icon
  will take you to the root directory of that drive.

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Shortcuts

• A shortcut is an alternate way to reach a file.
  Microsoft's term for a symbolic link, stored as a
  file with extension ".lnk".
• A shortcut does not actually hold any data. It
  has a shortcut property that specifies the path
  to the file where the data can be found. This
  file is called the target of the shortcut. A
  shortcut only refers to its target it is not a
  copy of the target.
• To create a shortcut
• right-click the icon for the file or folder that
  is to be the target
• select Create Shortcut from the pop-up menu).
• Note that you cannot create a shortcut to
  another shortcut.

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3.4.2 File Allocation Table (FAT) and NT File
System

• Clusters and File Allocation Tables Disks are
  divided into tracks and sectors.

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• Sectors hold a fixed number of bytes, typically
  512 bytes. One or more sectors are allocated to
  store a file. If the file contains only a line or
  two of text, it will fit into a fraction of one
  sector. In that case, the remainder of the sector
  is left unused.
• Because sectors are small, modern computer
  systems group them into clusters and read or
  write an entire cluster at a time.
• A cluster is the smallest amount of space any
  file can occupy on a disk. A cluster contains 4,
  8, 16, 32, or 64 adjacent sectors (the number
  must be a power of 2).

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• For each cluster that is part of a file, the FAT
  entry gives the number of the next cluster for
  that file. In this way, the clusters that make up
  a file are chained together, so if you know the
  address in the FAT of the first cluster of a
  file, you can find all the others by following
  the chain. The FAT entry for the last cluster in
  the chain contains a special marker to indicate
  that it is the end of the chain.

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• FAT16the FAT used 16 bits (two bytes) per entry,
  which allowed for a total of 216 or 65,536
  clusters. 512 (29) bytes per sector 64 (26)
  sectors per cluster 216 clusters in a FAT 16
  partition 231 bytes 2GB
• FAT32Windows 9x/2000/XP support a FAT32 file
  system. 32 bits (4 bytes) are used per entry, but
  the first 4 bits are reserved. smaller clusters
  can be used instead of larger FAT16 clusters.
  This leads to more efficient space allocation on
  the FAT32 drive

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• NT File System In NTFS, the cluster size is
  variable depending on the size of the logical
  drives. The cluster size is automatically
  determined by the NTFS Format utility, thereby,
  providing a level of flexibility. This
  flexibility is not available in FAT16 or FAT32.
  These features enable more efficient allocation
  of disk space.

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NTFS versus FAT

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Exercise 3

• Question 1. Preemptive Multitasking
• In this section you will use a Timestamp program
  and a graphical interface to examine how
  preemptive processing works.
• Before executing the program, answer the
  following questions in the context of an
  operating system
• a. What is a process?
• b. What does a process include?
• c. Name the possible states that a process can be
  in.
• d. What is a thread?
• e. Why are threads useful?

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Exercise 3

• Question 2. Virtual Memory
• In this section, you will use a program
  demonstrating how virtual memory is used.
• a. How does virtual memory work using a page
  table?
• b. What is the primary purpose of virtual memory?
• c. List three advantages of using virtual memory
  when executing a program.

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Exercise 3

• Question 3. Troubleshooting
• Below are various problem scenarios. Select the
  most likely cause(s) for the problem from the
  Causes list.
• CausesA. Component not plugged inB. Application
  software errorC. Operating system errorD. Low
  RAME. Slow processorF. CMOS battery failureG.
  Motherboard failureH. Hard disk failureI. BIOS
  ROM failureJ. Appropriate component driver not
  installed properly

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Exercise 3

• Problemsa. Program not respondingCauses
• b. Screen froze after successfully
  bootingCauses
• c. Programs running slowlyCauses
• d. Peripheral device not working (mouse,
  keyboard, printer)Causes

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Exercise 3

• e. All necessary computer system components are
  plugged in, but the system does not bootCauses
• f. The computer is being booted, and an error
  message indicates that the hard drive cannot be
  found.Causes
• g. If low memory is a cause of the system running
  slowly, what can you do as a user to speed up the
  system?

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Exercise 3

• Question 4. File Directories
• In this question, you are given a zip file, which
  contains some folders and files. You will unzip
  the given file, manipulate the files and folders,
  zip the resulting file structure and submit it,
  along with answers to the questions in this
  exercise.
• First, download and save SSD2 File System.zip
  onto your Desktop. Then unzip the file.

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Exercise 3

• a. What is the absolute path of the file named
  test.txt in SSD2 File System folder?
• b. How many parent directories does test.txt
  have?
• c. Create a shortcut of test.txt and place it in
  the same directory. Rename the shortcut MyTest.
  Copy and paste a screenshot showing the file
  property of MyTest.

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Exercise 3

• d. Examine the file property of test.txt. Explain
  why the values for Size and Size on disk are
  different. What is the term for the difference
  between the two sizes?
• e. Opening MyTest or test.txt both result in the
  display of the file. Explain the difference
  between MyTest and test.txt.
• f. What are the different file extensions in
  folder Temp1?
• g. List the most recently modified item in SSD2
  File System folder.