Operating Systems

Section A
Part one 1. a. Heap 2. c. An execution of program 3. a. without a break irrespective of size 4. C. Page replacement 5. b. To execute a procedure in another compute in the distributed system 6. b. High performance by serving several processes simultaneously 7. b. To execute a procedure in another compute in the distributed system 8. c. Multi-site transaction 9. c. Both a & b 10. d. 1 or more CPU

True and False 1. false 2. True 3. True 4. True 5. True 6. True 7. False 8. False 9. False 10. True

Section B

Answer 1)
It is a secure means to recognize a user when accessing government services online. The user remains anonymous, and the authentication process just confirms that the credential is valid and is in the hands of the owner of the credential. Credential authentication does not reveal or confirm identity to the government website. It receives only a message confirming that your credential (username/password) was successfully validated by your bank or by the government.

Answer 2)
File system a. Directory system for convenient grouping of files b. Protection of files against illegal access c. File sharing semantics d. Reliable storage of files
IOCS
a. Effecient operation of I/O devices b. Effecient access to records in file c. Invokes facilities through kernel d. Perform I/O operations without knowing the intricacies of I/O devices

Answer 3)
Instead of an actual memory location the segment information includes the address of a page table for the segment. When a program references a memory location the offset is translated to a memory address using the page table. A segment can be extended simply by allocating another memory page and adding to to the segment's page table.
An implementation of virtual memory on a system using segmentation with paging usually only moves individual pages back and forth between main memory and secondary storage, similar to a paged non-segmented system. Pages of the segment can be located anywhere in main memory and need not be contiguous. This usually results in less paging input/output and reduced memory fragmentation
Answer 4)
Deadlock characteristics 1. Permanent blocking of a set of processes that either compete for system resources or communicate with each other. 2. No efficient solutions 3. Involve conflicting needs for resources by two or more processes.
A deadlock situation can arise if the following four conditions hold simultaneously in a system: 4. Mutual exclusion:At least one resource must be held in a non-sharable mode; that is, only one process at a time can use the resource. If another process requests that resources, the requesting process must be delayed until the resource has been released. 5. Hold and wait:There must exist a process that is holding at least one resource and is waiting to acquire additional resources that are currently being held by other processes. 6. No preemption:Resources cannot be preempted; that is, resource can be released only voluntarily by the process holding it, after that process has completed its task. 7. Circular wait:There must exist a set {P0, P1,…, Pn} of waiting processes such that P0 is waiting for a resource that is held by P1, P1 is waiting for a resource that is held by P2, …, Pn-1 is waiting for resource that is held by Pn, and Pn is waiting for a resource that is held by P0.

Section C
Answer 1)
The design of an operating system architecture traditionally follows the separation of concerns principle. This principle suggests structuring the operating system into relatively independent parts that provide simple individual features, thus keeping the complexity of the design manageable.
Besides managing complexity, the structure of the operating system can influence key features such as robustness or efficiency:
The operating system possesses various privileges that allow it to access otherwise protected resources such as physical devices or application memory. When these privileges are granted to the individual parts of the operating system that require them, rather than to the operating system as a whole, the potential for both accidental and malicious privileges misuse is reduced.
Breaking the operating system into parts can have adverse effect on efficiency because of the overhead associated with communication between the individual parts. This overhead can be exacerbated when coupled with hardware mechanisms used to grant privileges.
The following sections outline typical approaches to structuring the operating system.
1. Monolithic Systems
A monolithic design of the operating system architecture makes no special accommodation for the special nature of the operating system. Although the design follows the separation of concerns, no attempt is made to restrict the privileges granted to the individual parts of the operating system. The entire operating system executes with maximum privileges. The communication overhead inside the monolithic operating system is the same as the communication overhead inside any other software, considered relatively low.
CP/M and DOS are simple examples of monolithic operating systems. Both CP/M and DOS are operating systems that share a single address space with the applications. In CP/M, the 16 bit address space starts with system variables and the application area and ends with three parts of the operating system, namely CCP (Console Command Processor), BDOS (Basic Disk Operating System) and BIOS (Basic Input/Output System). In DOS, the 20 bit address space starts with the array of interrupt vectors and the system variables, followed by the resident part of DOS and the application area and ending with a memory block used by the video card and BIOS.

Simple Monolithic Operating Systems Example

Most contemporary operating systems, including Linux and Windows, are also considered monolithic, even though their structure is certainly significantly different from the simple examples of CP/M and DOS.
2. Layered Systems
A layered design of the operating system architecture attempts to achieve robustness by structuring the architecture into layers with different privileges. The most privileged layer would contain code dealing with interrupt handling and context switching, the layers above that would follow with device drivers, memory management, file systems, user interface, and finally the least privileged layer would contain the applications.
MULTICS is a prominent example of a layered operating system, designed with eight layers formed into protection rings, whose boundaries could only be crossed using specialized instructions. Contemporary operating systems, however, do not use the layered design, as it is deemed too restrictive and requires specific hardware support.
3. Microkernel Systems
A microkernel design of the operating system architecture targets robustness. The privileges granted to the individual parts of the operating system are restricted as much as possible and the communication between the parts relies on a specialized communication mechanisms that enforce the privileges as necessary. The communication overhead inside the microkernel operating system can be higher than the communication overhead inside other software, however, research has shown this overhead to be manageable.
Experience with the microkernel design suggests that only very few individual parts of the operating system need to have more privileges than common applications. The microkernel design therefore leads to a small system kernel, accompanied by additional system applications that provide most of the operating system features.
MACH is a prominent example of a microkernel that has been used in contemporary operating systems, including the NextStep and OpenStep systems and, notably, OS X. Most research operating systems also qualify as microkernel operating systems.
4. Virtualized Systems
Attempts to simplify maintenance and improve utilization of operating systems that host multiple independent applications have lead to the idea of running multiple operating systems on the same computer. Similar to the manner in which the operating system kernel provides an isolated environment to each hosted application, virtualized systems introduce a hypervisor that provides an isolated environment to each hosted operating system.
Hypervisors can be introduced into the system architecture in different ways.
A native hypervisor runs on bare hardware, with the hosted operating systems residing above the hypervisor in the system structure. This makes it possible to implement an efficient hypervisor, paying the price of maintaining a hardware specific implementation.
A hosted hypervisor partially bypasses the need for a hardware specific implementation by running on top of another operating system. From the bottom up, the system structure then starts with the host operating system that includes the hypervisor, and then the guest operating systems, hosted above the hypervisor.
A combination of the native and the hosted approaches is also possible. The hypervisor can implement some of its features on bare hardware and consult the hosted operating systems for its other features. A common example of this approach is to implement the processor virtualization support on bare hardware and use a dedicated hosted operating system to access the devices that the hypervisor then virtualizes for the other hosted operating systems.

Section D
Answer 1) The process of identifying an individual, usually based on a username and password is called authentication. In security systems, authentication is distinct from authorization, which is the process of giving individuals access to system objects based on their identity. Authentication merely ensures that the individual is who he or she claims to be, but says nothing about the access rights of the individuals.

Authentication is the process of determining whether someone is, in fact, who or what it is declared to be. The process of identifying an individual, usually based on a username and password. In security systems, authentication is distinct from authorization, which is the process of giving individuals access to system objects based on their identity. Authentication merely ensures that the individual is who he or she claims to be, but says nothing about the access rights of the individual. It is also used for file protection for unauthorised users.
Some of the main reasons are discussed as below: * Monitoring – Since many devices (including firewall applications and appliances) can monitor the web activities on per user basis, administrators configure them to authenticate user accounts before allowing the users to access the external network. By doing so, the firewalls can log users’ activities. With the help of logs generated while monitoring activities of a user, administrators can assess and control the level of privileges that a culprit user gets. * Filtered Content – While working with the firewalls and configuring rule-sets and policies, administrators can also filter the incoming or outgoing contents. In order to configure the rule-sets and policies more granularly, administrators can configure user authentication to filter the contents on per user basis. With the help of filtered contents, administrators can restrict users from opening unwanted sites, or requesting or sending potentially unsafe and harmful packets. * Manage Time Allowance – Many firewall applications and appliances also allow administrators to manage time allowance. This means that they can specify the total duration of Internet access on each user basis. Making users authenticate their credentials help administrators to specify the total amount of duration for which users can access the Internet in every 24 hours. Time allowance also maintains proper discipline in an organization as users do not waste the Internet bandwidth by surfing the web unnecessarily. * Limit Time Duration – With the help of user authentication, security administrators can also specify the time of the day at which users are allowed to access the Internet or communicate with the external network. This process reduces unnecessary bandwidth consumption and decreases the chances of getting a network intruded with unauthorized people. When a particular time of the day is specified at which users can access the Internet, the configuration helps users to focus on their work instead of uselessly surfing the Internet. * Bandwidth Allocation – Most firewall applications or appliances also allow administrators to allocate bandwidth on per user basis. While using such firewalls, administrators can limit the maximum amount of bandwidth a particular user or group of users can consume. With the help of such bandwidth management system, administrators can remarkably reduce the useless consumption of available bandwidth. * Frequency of security breaches (i.e. Twitter, Evernote, LinkedIn) have IT departments paying closer attention to authentication. * Ubiquity of mobile devices is not only increasing the number of online apps that users need to log in to, but also increasingly becoming the device of choice for assisting in authentication. According to Allan, in the past few years, the popularity of phone-as-a-token solutions has overtaken one-time password hardware tokens in terms of new and refreshed deployments. * Enhanced methods of authentication have “morphed from traditional tokens to USB devices to smart cards to fingerprint readers, soft tokens and scanning devices.” Contextual authentication, based on analytics of behavior patterns and device patterns, is growing in importance and more vendors are offering it with their core user authentication products. Additionally, there is an increased interest in using biometrics for a higher level of assurance with improved user experience, including form factors like typing rhythm, voice recognition, face topography and iris structure. * Move to cloud-delivered user authentication services is becoming more widely adopted and having the most traction among small and mid-sized businesses and industries where TCO is a more significant consideration. Gartner predicts that by 2017, more than 50% of enterprises will choose cloud-based services – up from less than 10% today.