24 Computer Architecture and Organization
hardware. Therefore, unlike other modules, essentially, this module is restricted within the processor
itself. Detailed discussions related to this module would be presented through Chapters 5, 6, 9 and 10
of this book.
2.5.3 Operating System
The responsibility of the next building block—the operating system—is to relieve the user (or in other
terms, the user program) from the burden of interacting directly with so many complexities of the sys-
tem hardware. Thus, the operating system controls all available resources of the computer, available
in the form of hardware and software, and initiates all details for any interaction between any of these
and the user’s command or user’s program. In other words, the operating system is the window through
which the application programs interact with the system hardware. In Chapter 11, we would resume our
discussions on operating system.
2.5.4 User’s Program
This is the outermost module of computer and normal users interact directly through this module. All
application programs, user’s command, assemblers, compilers and so on occupy this module. Programs
developed with C, C++ or Java occupy this module. To be precise, the languages used in this module
are not the cryptic machine language in binary but the high level languages.
SUMMARY
A computer may be interfaced with many external devices, depending upon the user’s need. Some of
these essential devices are display, keyboard, mouse, printer, etc. Other such devices may be digitizer,
XY-plotter, ADC, DAC, magnetic tape drives and so on. Internally, within the system, we nd a moth-
erboard, apart from SMPS, for power supply, and HDD, for data storage.
The motherboard accommodates a processor (CPU) and some peripheral devices (to make it work),
e.g., main memory (RAM and ROM), input/output controller, timers, interrupt controller and so on.
All these peripheral devices are interfaced with the processor through the system bus (internal), which
is composed of address, data and control signals. External devices are interfaced with the processor
through asynchronous external bus. As long as it is operational, the processor continuously fetches
instruction bytes from main memory and keeps on decoding and executing those instructions.
A computer may be visualized to be composed of different building blocks. Broadly, they might be
categorized as digital logic, microarchitecture, operating system and, nally, the user’s program or ap-
plication programs. These are elaborated in the rest of the chapters of this book.
POINTS TO REMEMBER
R Internal bus is synchronous, while external bus is asynchronous.
R As long as operational, processor continuously fetches, decodes and executes instruction after
instruction.
R Processor can execute a program in main memory but not in secondary memory.
M02_GHOS1557_01_SE_C02.indd 24M02_GHOS1557_01_SE_C02.indd 24 4/29/11 5:00 PM4/29/11 5:00 PM
..................Content has been hidden....................
You can't read the all page of ebook, please click here login for view all page.