‫اململكة العربية السعودية‬
Kingdom of Saudi Arabia
Ministry of Higher Education
Prince Sattam Bin Abdul-Aziz University
College of Computer
Engineering and sciences
‫وزارة التعليم العايل‬
‫جامـعـة األمري سطام بن عبدالعزيز‬
‫كل ـي ــة هـنــدس ــة وعلـ ــوم احلـاســب‬
2440 & 2544 :‫الشعبة‬
Course Title: CS3701-Operating System
CSC3701
Instructor Name: Mr. Abdul Haseeb Khan
Tutorial Lecture # 01
CH: Introduction to Operating
Week# 01
System
Date: 31-08-2015
Objective: Introduction basic concepts of operating system
Q. 1 what is an operating system?
Answer:
It is a program that acts as an intermediary between the user and the computer hardware.
It makes it easy for the user to use the computer hardware. It enables efficient use of the
computer hardware by acting as a resource allocator.
Q. 2 draw a diagram showing relative position of the components of a computer system:
the hardware, the operating system, the system and application programs and the users.
Answer:
See the book or slides.
Q. 3 how do a computer system boot or start-up?
Answer:
All computer systems have a bootstrap program, which gets executed automatically at
power up. The bootstrap program is permanently stored in a ROM. Bootstrap program
loads the OS kernel into the main memory and starts its execution. Once started OS waits
for an event to happen, such as user typing in a command.
Q. 4 draw a diagram showing internal components: CPU, memory, USB controller, etc.
organized around a common bus.
Answer:
See the book or slides.
Q.5 What is an interrupt? What is a trap?
Answer:
Interrupt is a hardware signal or an instruction that causes CPU to stop what it is doing
and execute a routine to handle the interrupt. The routine is called interrupt service
routine. On completion the CPU resumes the interrupted computation.
A trap is a software generated interrupt caused either by an error or a user request.
Q. 6 how are interrupts handled by the CPU?
Answer:
1. CPU stops what it is doing and transfers execution to a fixed location (in an
interrupt vector. See the question below). The fixed location contains the starting
address of the interrupt service routine. The values of various registers in the CPU
and program counter are saved.
2. The interrupt service routine is executed.
3. Values of various registers and program counter, previously stored, are restored.
CPU resumes the interrupted computation.
Q. 7 what is an interrupt vector?
Answer:
It is an array of memory locations that stores the addresses of the interrupt service
routines.
Q. 8 what is a synchronous and asynchronous I/O?
Answer:
Synchronous I/O – after I/O starts, CPU waits for the I/O to finish and control returns to
the user program only after I/O completion.
Asynchronous I/O -- after I/O starts, control returns to the user program without waiting
for I/O completion. Example: I/O through DMA.
Q. Draw the diagram showing the timelines for each type.
See the book or the slides.
Q. 9 what is device status table?
Device status table contains entry for each I/O device indicating its type, address and
state. Used during I/O.
Q. 10 what is Direct Memory Access (DMA) transfer?
It is a type of I/O in which a block of data is transferred from the buffer storage directly
to the main memory without CPU intervention. DMA is much faster than I/O in which
CPU transfers small amounts of data.
Q. 11 what are device controllers and device drivers? How are they used during I/O?
Answer:
(a) Each device in a computer system (e.g. keyboard, disk drive, etc.) has a device
controller, usually in the form of an IC chip, connected to the bus. The device
controller has buffer storage and some registers. Device controller is responsible
for moving data between the devices it controls to its buffer storage.
OS have device drivers for each device controller. Device driver understands the
device controller and presents a uniform interface to the device to the rest of the
operating system.
(b) To start an I/O operation, the device driver loads the appropriate registers in the
device controller. The device controller, in turn, decodes the contents of these
registers to determine the action to take (such as “read a character from the
keyboard”). The controller transfers data from the device to its local buffer. Once
the transfer is complete the controller informs the device driver via an interrupt
that it has finished the operation. Device driver then returns control to the
operating system with data and status information.
Q. 12 List various type of storage used in a computer system and give capacity and speed
(access time) of each type. Draw the storage hierarchy.
Answer:
See the slides or the book.
Q. 13 what is caching?
Answer:
Cache is type of memory that has very low access time (it is high speed). To improve the
speed of computation (or performance) data that is frequently needed during computation
is copied from the high-access time (or low speed) main or secondary memory and kept
in the cache, where it can be accessed quickly. This process is called caching.
Q. 14 what are single-processor systems and multi-processor systems?
In a single-processor system, there is one main CPU capable of executing a general
purpose instruction set. Multi-processor systems have more than one CPU connected to
the same bus and sharing other resources such as memory, devices etc. Multi-processor
systems are also known as parallel systems or tightly-coupled systems.
Q. 15 what is the difference between symmetric and asymmetric multiprocessing?
Answer:
In asymmetric multiprocessing each processor is assigned a specific task. A master
processor controls the system; other processors take instructions from the master
processor or have predefined tasks. In symmetric multiprocessing each processor
performs all tasks within the operating system.
Q. 16 what is an interactive system?
Answer:
A computer system in which user gives instructions/commands to the system directly
through a keyboard or a mouse and waits for the system to respond back through an
output device such as a monitor. The response time of an interactive system is less than
one second.
Q. 17 what are multi-programmed and non-multi-programmed systems?
Answer:
In a multi-programmed system OS keeps many jobs in the memory. It picks up and starts
execution of one of the jobs. When the job has to wait for some task, such as I/O
operation to complete, OS switches to and starts execution of another job. Similarly when
that job has to wait, OS switches to another job and so on. CPU never remains idle.
In a non-multi-programmed system the OS does not switch to another job but waits for
the I/O to complete. CPU remains idle during this time.
Q. 18 what is the advantage of multi-programming?
Answer:
Multi-programming enables efficient utilization of system resources such as CPU,
memory and peripheral devices.
Q. 19 briefly describe timesharing or multitasking?
Answer:
Time shared or multi tasked system is a multi-programmed system in which CPU
executes multiple jobs by switching among them, but the switches occur after a job is
executed for a short period of time or the job has to wait for an I/O. The CPU time
allocated to a job is called its time slice and can be very short, for example, a few milliseconds. Since the job switches happen quickly multiple users are able to work with the
system interactively at the same time.
Q. 20 what is a process?
Answer:
A program loaded into the memory and under execution is called a process.
Q. 21 Name the two modes in which a computer system can operate.
Answer:
(i)
Kernel mode (also known as system mode, supervisor mode or privileged
mode). In this mode the CPU runs/executes operating system code.
(ii)
User mode. In this mode the CPU runs/executes a user program.
Q. 22 Why is it necessary to have two modes of operation for a computer system?
Answer:
User programs can be incorrectly written, malicious or may generate errors. They can
interfere with the functioning of the OS. For example, a user program can overwrite
operating system code with data. For this reason two modes of operation are provided:
user mode and kernel mode. Some instructions can only be executed in kernel mode and
not in user mode; certain areas of memory can also be accessed only in kernel mode. The
two modes are distinguished by a mode bit in the hardware. Mode bit is 1 in user mode
and 0 in kernel mode.
Q. 23 Name various computing environments.
Answer:
a. Batch
b. Interactive
c. Time sharing
d. Real time
e. Network
f. Parallel
g. Distributed
Q. 24 what do the following terms mean? Kernel, BIOS, firmware, bus, routine, system
call, process, job, job pool
Answer:
Kernel: In computing, the kernel is the main component of most computer operating
systems; it is a bridge between applications and the actual data processing done at the
hardware level. The kernel's responsibilities include managing the system's resources (the
communication between hardware and software components). Usually, as a basic component
of an operating system, a kernel can provide the lowest-level abstraction layer for the
resources (especially processors and I/O devices) that application software must control to
perform
its
function.
It
typically
makes
these
facilities
available
to application processes through inter-process communication mechanisms and system calls.
2nd Definition:
In computing, the kernel is a computer program that manages I/O (input/output) requests
from software, and translates them into data processing instructions for the central processing
unit and other electronic components of a computer. The kernel is a fundamental part of a
modern computer's operating system.
When a computer program (in this context called a process) makes requests of the kernel, the
request is called a system call. Various kernel designs differ in how they manage system calls
and resources. For example, a monolithic kernel executes all the operating
system instructions in the same address space in order to improve the performance
[clarification needed] of the system. A microkernel runs most of the operating
system's background
processes in user
space to
make
the
operating
system
more modular and, therefore, easier to maintain.
(For others see Book.)