Introduction to CS

Project 6: Operating Systems - Answers

Using the information on the class website, answer the following questions in an MS Word document:

  1. What is an OS?
    • An OS, Operating System, is a large software program that organizes and controls hardware and software so that the device it lives in behaves in a flexible but predictable way..
  2. What are the main functions of an OS?
    • At the simplest level, an operating system does two things:
      1. It manages the hardware and software resources of the system. In a desktop computer, these resources include such things as the processor, memory, disk space and more (On a cell phone, they include the keypad, the screen, the address book, the phone dialer, the battery and the network connection).
      2. It provides a stable, consistent way for applications to deal with the hardware without having to know all the details of the hardware.
  3. How does an OS work?
    • After the power-on self test (POST) finishes and the basic input-output systems (BIOS) executes, the first piece of the operating system: the bootstrap loader begins its single function: It loads the operating system into memory. Once loaded, the OS begins its tasks that fall into six categories:
      1. Processor management
      2. Memory management
      3. Device management
      4. Storage management
      5. Application inerface
      6. User interface
  4. What are the four main types of an OS?
    • The four main categories are:
      1. RTOS Real Time Operating System
      2. Single User, Single Task
      3. Single User, Multi Task
      4. Multi User, Multi Task
  5. What are the major OS's available today and what type are they?
      1. Windows FAT & NTFS - Single-user, Multi-tasking
      2. MacOS - Single-user, Multi-tasking - varient of UNIX
      3. Unix - Multi-user, Multi-tasking
  6. What is FAT?
    • A file system is a part of the operating system that determines how files are named, stored, and organized on a volume. A file system manages files and folders, and the information needed to locate and access these items by local and remote users.
    • FAT stands for File Allocation Table. Files are broken into records and these records are stored on the hard disk in different sectors. The File Allocation Table stores is an index of stored files. The index indicates where the first record of the file is stored, and other information about the files. The stored records may or may not be sequential and after a while, the hard disc may become very fragmented requiring the user to perform a "defrag" to improve the performance of the computer.
    • FAT file systems are associated with the number of bits utilized for a file allocation table entry. For instance, FAT16 utilizes a 16-bit file allocation table entry, and FAT32 utilizes a 32-bit file allocation table entry. FAT16 works effectively on small disks and uncomplicated folder structures, while FAT32 works effectively on large disks that have intricate folder structures.
    • FAT16 generally works well in managing disk space when the size of the volume is less than 256MB. You should refrain from using FAT16 on volumes that are larger than 512MB. FAT16 cannot be utilized on volumes that exceed 4 GB.
    • FAT32 can support partitions up to 2047 GB in size compared to FAT16's 4 GB. With FAT32, there is no restriction on the number of entries that the root folder can contain.
  7. What is NTFS?
    • A file system is a part of the operating system that determines how files are named, stored, and organized on a volume. A file system manages files and folders, and the information needed to locate and access these items by local and remote users.
    • New Technology File System. NTFS is the disk file structure used by Window NT and Windows 2000, which has a Master File Table instead of a FAT.
    • NTFS provides performance, reliability, and advanced features not found in FAT. For example, NTFS includes built-in security features such as file and folder permissions and the Encrypting File System (EFS), which is the technology used to store encrypted files on NTFS volumes. NTFS also provides support for volumes up to 256 terabytes in size, support for disk quotas and compression, and support for mounted drives.
  8. Which is better, FAT or NTFS for today's systems and why?
    • For most users running Windows XP, NTFS is the obvious choice. It's more powerful and offers security advantages not found in the other file systems. However, if you are running a dual-boot system - more than one operating system, you will definitely need to format some of your volumes as FAT. Any programs or data that need to be accessed by more than one operating system on that computer should be stored on a FAT16 or possibly FAT32 volume.
  9. What is UNIX?
    • UNIX is an operating system that was created in an effort to provide a multiuser, multitasking system. It is an Open Operating System, or a standard upon which organizations and companies base their own systems. The UNIX operating system comprises three parts: The kernel, the standard utility programs, and the system configuration files.
    • Because the Unix operating system is an Open Operating System you will discover that there are various shells - such as B-shell, C-shell, or K-shell. The shell is a type of program called an interpreter. (Windows uses the command interpreter.)
    • Unlike windows, The UNIX operating system is a multitasking system - it will simultaneously perform multiple tasks.
    • Unlike DOS, the UNIX shell is case-sensitive.
  10. How does the UNIX file system work?
    • The UNIX filesystem is heirarchical (resembling a tree structure). The tree is anchored at a place called the root, designated by a slash "/". To decribe a specific location in the filesystem heirarchy, you must specify a "path." The path to a location can be defined as an absolute path from the root anchor point, or as a relative path, starting from the current location.
    • Every file and directory has associated with it ownership, and access permissions. Furthermore, one is able to specify those to whom the permissions apply. Permissions are defined as read, write, and execute. Those to whom the permissions apply are the user who owns the file, those who are in the same group as the owner, and all others.
    • Every item in a UNIX file system can de defined as belonging to one of four possible types:
      1. Ordinary files
      2. Directories
      3. Special files
      4. Links
    • Each line in a directory file contains only the name of the item, and a numerical reference to the location of the item. The reference is called an i-number, and is an index to a table known as the i-list. The i-list is a complete list of all the storage space available to the file system.
    • A UNIX machine may be connected to several file systems, each with its own i-list. One of those i-lists points to a special storage area, known as the root file system. The purpose of the i-list is to provide the operating system with a map into the memory of some physical storage device.
    • Each entry in an i-list is called an i-node. An i-node contains 10 direct pointers, which point to disk blocks on the storage device. In addition, each i-node also contains one indirect pointer, one double indirect pointer, and one triple indirect pointer. The indirect pointer points to a block of direct pointers. The double indirect pointer points to a block of indirect pointers, and the triple indirect pointer points to a block of double indirect pointers. By structuring the pointers in a geometric fashion, a single i-node can represent a very large file.

    • Each file system that is mounted on a UNIX machine is accessed through its own block special file. The information on each of the block special files is kept in a system database called the file system table, and is usually located in /etc/fstab. It includes information about the name of the device, the directory name under which it will be mounted, and the read and write privileges for the device.