• Course: CS110
• Name: SooYoung Jung
• Home Assignment #1
• Due Date: 9/3/00
• Date: 9/3/00
• Formatter: HTML

1. S.1.7, pg. 21, Define the essential properties of the following types of operating systems: Batch, Interactive, Time Sharing, Real Time, and Distributed.

• Batch : Batch system uses the common input devices such as card readers and tape drives to collect the data.  This collected data was inputted at once as a group and processed. System would not be available until finishing the job.  When the system became available, then system would run other batch.
• Interactive : An interactive computer system provides on-line communication between the user and the system.  The user gives instructions to the operating system or to a program directly, and receives an immediate response.
• Time Sharing : Time-shared operating systems allow many users to use a computer system interactively at the same time.  Multiprogramming allows time sharing.
• Real Time : A real-time system is used when there are rigid time requirements on the operation of a processor or the flow of data, and thus is often used as a control device in a dedicated application.  
• Distributed : A distributed system is a collection of processors that do not share memory or a clock.  Instead, each processor has its own local memory, and the processors communicate with one another through various communication lines, such as high-speed buses or telephone lines.  A distributed system provides the user with access to the various resources located at remote sites.

2. s.2.2, How does the distinction between monitor mode and user mode function as a rudimentary form of protection (security) system?

• The Operating system must ensure correct operating of the computer system.  Hardware has two modes to prevent user programs from interfering with the proper operation of the system, which are user mode and monitor mode.  Various instructions are privileged, and can be executed in only monitor mode.

3. s.2.3, What are the differences between a trap and an interrupt? What is the use of each function?

• A trap is a software-generated interrupt caused either by an error, or by a specific request from a user program that an operating-system service by performed.  An interrupt is a signal that gets the attention of the CPU and is usually generated when I/O is required.  When a trap occurs, the hardware transfers control to the operating system.

4. Tanenbaum #1.6, pg 26, Which of the following instructions should be allowed only in kernel mode?

1. Disable all interrupts
2. Read the time-of-day clock
3. Set the time-of-day clock
4. Change the memory map

• Only #2 should be allowed in kernel mode.

5. Tanenbaum #1.12, pg 26, Why is the process table needed in a timesharing system? Is it also needed in personal computer systems in which only one process exists, that process taking over the entire machine until it is finished?

• The process table is only needed in a timesharing system.  The process table is to store the job process which will be processed later.  As a result, the process table is not needed in personal computer systems which will always have one jot to process.

6. Tanenbaum #2.3, pg 71, Explain the difference between busy waiting and blocking.

• Busy waiting is a loop that reads the status register over and over until the busy bit becomes clear. Blocking is a situation where process wait indefinitely within the semaphore.