Questions and Answers of Computer Engineering

You can use simple estimates to compare the cost and performance of a terabyte storage System made entirely from disks with one that incorporates tertiary storage. Suppose that magnetic disks each
Why would it be a bad idea for gateways to pass broadcast packets between networks? What would be the advantages of doing so?
Suppose that a one-sided 5.25-inch optical-disk cartridge has an a real density of 1 gigabit per square inch. Suppose that a magnetic tape has an areal density of 20 megabits per square inch, and is
a. How many disk drives would be required to hold 4 exabytes of data? b. How many magnetic tapes would be required to hold 4 exabytes of data? c. How many optical tapes would be required to hold 4
Discuss how an operating system could maintain a free-space list for a tape-resident file system. Assume that the tape technology is append-only and that it uses the EOT mark and locate, space, and
What are two main differences between a WAN and a LAN?
Explain why a doubling of the speed of the systems on an Ethernet segment may result in decreased network performance. What changes could be made to ameliorate the problem?
Under what circumstances is a token-ring network more effective than an Ethernet network?
In what ways is using a name server better than using static host tables? What are the problems and complications associated with name servers? What methods could be used to decrease the amount of
Of what use is an address resolution protocol? Why is the use of such a protocol better than making each host read each packet to determine to whom it is destined? Does a token-ring network need such
What are the advantages and disadvantages of making the computer network transparent to the user?
Is it always crucial to know that the message you have sent has arrived at its destination safely? If your answer is “yes,” explain why. If your answer is “no,” give appropriate examples.
What would be the effect on cost and performance if tape storage were to achieve the same a real density as disk storage?
What are the main differences between capability lists and access lists?
A Burroughs B7000/B6000 MCP file can be tagged as sensitive data. When such a file is deleted, its storage area is overwritten by some random bits. For what purpose would such a scheme be useful?
In a ring-protection system, level 0 has the greatest access to objects, and level n (greater than zero) has fewer access rights. The access rights of a program at a particular level in the ring
Consider a system in which “computer games” can be played by students only between 10 P.M. and 6 A.M., by faculty members between 5 P.M. and 8 A.M., and by the computer center staff at all times,
What is the need-to-know principle? Why is it important for a protection system to adhere to this principle?
A password may become known to other users in a variety of ways. Is there a simple method for detecting that such an event has occurred? Explain your answer.
The list of all passwords is kept within the operating system. Thus, if a user manages to read this list, password protection is no longer provided. Suggest a scheme that will avoid this problem.
The UNIX program, COPS, scans a given system for possible security holes and alerts the user to possible problems. What are the potential hazards of using such a system for security? How can these
Discuss ways by which managers of systems connected to the Internet could have limited or eliminated the damage done by the worm. What are the drawbacks of making such changes to the way in which the
Make a list of security concerns for a computer system for a bank. For each item on your list, state whether this concern relates to physical security, human security, or operating system security.
What are two advantages of encrypting data stored in the computer system?
Linux runs on a variety of hardware platforms. What steps must the Linux developers take to ensure that the system is portable to different processors and memory-management architectures, and to
Dynamically loadable kernel modules give flexibility when drivers are added to a system, but do they have disadvantages too? Under what circumstances would a kernel be compiled into a single binary
Multithreading is a commonly used programming technique. Describe three different ways that threads could be implemented. Explain how these ways compare to the Linux clone mechanism. When might each
What are the extra costs incurred by the creation and scheduling of a process, as compared to the cost of a cloned thread?
The Linux scheduler implements soft real-time scheduling. What features are missing that is necessary for some real-time programming tasks? How might they be added to the kernel?
The Linux kernel does not allow paging out of kernel memory. What effect does this restriction have on the kernel’s design? What are two advantages and two disadvantages of this design decision?
In Linux, shared libraries perform many operations central to the operating system. What is the advantage of keeping this functionality out of the kernel? Are there any drawbacks? Explain your
What are three advantages of dynamic (shared) linkage of libraries compared to static linkage? What are two cases where static linkage is preferable?
Compare the use of networking sockets with the use of shared memory as a mechanism for communicating data between processes on a single computer. What are the advantages of each method? When might
UNIX systems used to use disk-layout optimizations based on the rotation position of disk data, but modern implementations, including Linux, simply optimize for sequential data access. Why do they do
The Linux source code is freely and widely available over the Internet or from CD-Rom vendors. What three implications does this availability have on the security of the Linux system?
What are some reasons why moving the graphics code in Windows NT from user mode to kernel mode might decrease the reliability of the system? Which of the original design goals for Windows NT does
The Windows 2000 VM manager uses a two-stage process to allocate memory. Identify several ways in which this approach is beneficial?
Discuss some advantages and some disadvantages of the particular page-table structure used in Windows 2000.
What is the purpose of a prototype page-table entry in Windows 2000?
What changes would be needed for Windows 2000 to run a process that uses a 64-bit address space?
Windows 2000 has a centralized cache manager. What are the advantages and disadvantages of this cache manager?
Windows 2000 uses a packet-driven I/O system. Discuss the pros and cons of the packet driven approach to I/O.
How were the design goals of UNIX different from those of other operating systems during the early stages of UNIX development?
Why are many different versions of UNIX currently available? In what ways is this diversity an advantage to UNIX? In what ways is it a disadvantage?
What are the advantages and disadvantages of writing an operating system in a high-level language, such as C?
In what circumstances is the system-call sequence fork execve most appropriate? When is v fork preferable?
Does FreeBSD give scheduling priority to I/O or CPU-bound processes? For what reason does it differentiate between these categories, and why is one given priority over the other? How does it know
Early UNIX systems used swapping for memory management, whereas 4.3BSD used paging and swapping. Discuss the advantages and disadvantages of the two memory methods.
Describe the modifications to a file system that the Free BSD makes when a process requests the creation of a new file /tmp/foo and writes to that file sequentially until the file size reaches 20 KB.
Directory blocks in FreeBSD are written synchronously when they are changed. Consider what would happen if they were written asynchronously. Describe the state of the file system if a crash occurred
What effects on system performance would the following changes to FreeBSD have? Explain your answers. a. The merging of the block buffer cache and the process paging space b. Clustering disk I/O
What socket type should be used to implement an inter computer file-transfer program? What type should be used for a program that periodically tests to see whether another computer is up on the
What three features of Mach make it appropriate for distributed processing?
Name two ways that port sets are useful in implementing parallel programs?
Consider an application that maintains a database of information, and provides facilities for other tasks to add, delete, and query the database. Give three configurations of ports, threads, and
Give the outline of a task that would migrate subtasks (tasks it creates) to other systems. Include information about how it would decide when to migrate tasks, which tasks to migrate, and how the
Why would someone use the low-level system calls, instead of the C Threads package?
Why are external memory managers not able to replace the internal page-replacement algorithms? What information would need to be made available to the external managers for the latter to make
Why is it difficult to implement mutual exclusion and condition variables in an environment? Where like CPUs do not share any memory? What approach and mechanism could be used to make such features
What are the advantages to rewriting the 4.3BSD code as an external, user-level library, rather than leaving it as part of the Mach kernel? Are there any disadvantages? Explain your answer.
Suppose the hypothetical processor of also has two I/O instructions: 0011 = Load AC from I/O 0111 = Store AC to I/O In these cases, the 12-bit address identifies a particular external
Suppose the hypothetical processor of also has two I/O instructions: 0011 = Load AC from I/O 0111 = Store AC to I/O In these cases, the 12-bit address identifies a particular external
The program execution of Figure 1.4 is described in the text using six steps. Expand this description to show the use of the MAR and MBR.
Consider a hypothetical 32-bit microprocessor having 32-bit instructions composed of two fields. The first byte contains the opcode and the remainder an immediate operand or an operand address. a.
Consider a hypothetical microprocessor generating a 16-bit address (for example, assume that the program counter and the address registers are 16 bits wide) and having a 16-bit data bus. a. What is
Consider a 32-bit microprocessor, with a 16-bit external data bus, driven by an 8-MHz input clock. Assume that this microprocessor has a bus cycle whose minimum duration equals four input clock
Consider a computer system that contains an I/O module controlling a simple keyboard/ printer Teletype. The following registers are contained in the CPU and connected directly to the system
In virtually all systems that include DMA modules, DMA access to main memory is given higher priority than processor access to main memory. Why?
A DMA module is transferring characters to main memory from an external device transmitting at 9600 bits per second (bps).The processor can fetch instructions at the rate of 1 million instructions
A computer consists of a CPU and an I/O device D connected to main memory Mvia a shared bus with a data bus width of one word. The CPU can execute a maximum of 106 instructions per second. An average
Consider the following code: For (i = 0; i < 20; i++) For (j = 0; j < 10; j++) A[i] = a [i] * j a. Give one example of the spatial locality in the code. b. Give one example of the temporal
Generalize Equations (1.1) and (1.2) in Appendix 1 A to n-level memory hierarchies.
Consider a memory system with the following parameters: Tc = 100 ns Cc = 0.01 cents/bit Tm = 1200 ns Cm = 0.001 cents/bit a. What is the cost of 1 MByte of main memory? b. What is the cost of 1
A computer has a cache, main memory, and a disk used for virtual memory. If a referenced word is in the cache, 20 ns are required to access it. If it is in main memory but not in the cache, 60 ns are
Suppose a stack is to be used by the processor to manage procedure calls and returns. Can the program counter be eliminated by using the top of the stack as a program counter?
Suppose that we have a multiprogrammed computer in which each job has identical characteristics. In one computation period, T, for a job, half the time is spent in I/O and the other half in processor
An I/O-bound program is one that, if run alone, would spend more time waiting for I/O than using the processor. A processor-bound program is the opposite. Suppose a short-term scheduling algorithm
Contrast the scheduling policies you might use when trying to optimize a time-sharing system with those you would use to optimize a multiprogrammed batch system.
What is the purpose of system calls, and how do system calls relate to the OS and to the concept of dual-mode (kernel mode and user mode) operation?
What is an instruction trace?
What common events lead to the creation of a process?
For the processing model of Figure 3.6, briefly define each state.
What does it mean to preempt a process?
What is swapping and what is its purpose?
Why does Figure 3.9b have two blocked states?
List four characteristics of a suspended process.
For what types of entities does the OS maintain tables of information for management purposes?
List three general categories of information in a process control block.
Why are two modes (user and kernel) needed?
What are the steps performed by an OS to create a new process?
What is the difference between an interrupt and a trap?
Give three examples of an interrupt.
What is the difference between a mode switch and a process switch?
Name five major activities of an OS with respect to process management, and briefly describe why each is required.
Table 3.5 lists typical elements found in a process control block for an unthreaded OS. Of these, which should belong to a thread control block and which should belong to a process control block for
List reasons why a mode switch between threads may be cheaper than a mode switch between processes.
What are the two separate and potentially independent characteristics embodied in the concept of process?
Give four general examples of the use of threads in a single-user multiprocessing system.
What resources are typically shared by all of the threads of a process?
List three advantages of ULTs over KLTs.

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