Lorenzo Alvisi

Lorenzo Alvisi

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  • cours magistral - matière potentielle : notes
  • mémoire - matière potentielle : through speculation
  • mémoire - matière potentielle : architectures
Lorenzo Alvisi Department of Computer Sciences Taylor Hall 2.124 The University of Texas at Austin Austin, Texas 78712 phone: (512) 471-9792 fax: (512) 232-7886 email: http: // A Education Ph.D. Computer Science, Cornell University, 1996. M.S. Computer Science, Cornell University, 1994. Post-graduate degree Physics, University of Bologna, Italy, 1989.
  • r. kotla
  • j. p. martin
  • a. clement
  • s. rao
  • protocols
  • proceedings
  • symposium
  • best paper award
  • fault
  • systems

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A CST PUBLICATIONOW IT WORKS
By Rakesh Mohan Hallen
Designed and illustrated by
Ankur Mitra
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A computer is an information-processing
machine, an electronic device,
manufactured in a factory, that can perform
many functions-till now done by humans
only. It can see, listen, read, write, speak,
show, learn, remember, think, analyse and
They have started invading our life. decide. In short, it can communicate
They are almost everywhere, offices, intelligently. It can do so not only with
banks, railway stations, post humans but also with other computers.
schools, colleges...our homes! They are It needs electricity from the main power line
called computers. Just as the inventions of to be alive. Without electricity, a computer is
the train and the motor car revolutionized a dead body. If a computer is connected to
the way we travel from one place to a UPS (Uninterrupted Power Supply) or
another, computers have the a battery, it can work for a short duration
way we remember, write or communicate. even when there is no electricity.
Not only do they help us to draft a letter, Just as our body has many organs, each
a report or a book, but also to send it of which has a particular function, the body
anywhere even without using any paper! of a computer is also made up of several
They can like a radio or television also parts. Like our brain that controls other
be used to share our thoughts, our parts of our body, in a computer there is
emotions, our creations with many people, a device called a microprocessor that
all at once. allows it to take decisions and control its
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various parts. We have memory to
retain information and ways to do various There are several types of computers
tasks, so has a computer. We have a Palmtop, Laptop, Desktop, Server,
Mainframe and Supercomputer. A Palmtopface, a mouth and limbs to express
ourselves, a computer has a screen Gust is the smallest and looks like an overgrown
like that of a TV) that acts like its face, calculator. It can be held in one's palm.
A Laptop looks like a large book that cana device called mouse is like its limb which
can also write, draw and paint, and a small be kept on your lap while you work on it
loudspeaker that enables it to speak or and can accompany you anywhere. Both
sing. We have eyes, ears, nose and a Laptop and a Palmtop work by using the
skin to help us know our environment.
Similarly, a computer has an operating
system through which you can instruct it to
perform various tasks. Some computers
can also hear voices, see objects and
sense touch through
a microphone, a camera
and a touch screen.
, 101010101010101010101010101010101010101010101010101010101010101010101101010101010101010101010101010101010101010101010101010101010101010101010101
c=. P -stored electricity from a battery. But the
computers we come across most often
belong to the family Desktop (nickname
PC). A Desktop has a relatively large
body and is usually made up of four
detachable parts: one part looks like
a small TV and is called a 'monitor'; the
second part resembles the keyboard of
a typewriter and is called 'keyboard'; the •
third, looks like a trendy box, called the GUI and Mouse
'Central Processing Unit' (or just CPU); and The ancestors of the present generation
the fourth looks like a mouse and is called of computers, born in about 1920, did little
the 'mouse'. A number ot other devices, more than a few rather hefty calculations.
known as computer peripherals like, web Obviously, they were not very popular.
camera, speaker, microphone and printer, Leaders in the computer industry, like the
often accompany it like faithful assistants. IBM (International Business Machines)
They enable it to see, hear, speak, or executives, felt that they could sell at best
deliver desired results. Servers, Mainframes a few thousand computers worldwide. After
and Supercomputers are the heavyweight all, how many people would be interested
members of the family. We seldom come in investing a fortune just to calculate
across them, but they are very important faster! Besides, these computers could
as they manage many PCs, keeping them occupy a big air-conditioned hall and
connected and in touch with each other. consume a lot of electricity. People could
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interact with them only through a pack of
punched cards. Often it took a few hours
before one got a printed output (there were
no screens to see it). It is only after the birth
of the PC, which has evolved in the last two
decades, that the computers have become
common and versatile. The punched card,
or even the keyboard, is no more essential choose the picture. On the picture, there
for people to interact with a computer. are some icons with a brief title. This
A user friendly Graphic User Interface display is known as the GUI. Moreover,
(popularly known as GUI) and a pointing in order to do a particular task on the PC,
device (like the mouse) have made one does not need to type in a command,
interaction much more effortless and easy. just a click of the mouse button is
sufficient. ~When the first PC came into being, the
screen of the monitor invariably used to be A mouse is a small plastic encased
black and often blank to begin with. One device, which can be used to control the
was then required to remember and type position of the pointer, called the cursor,
in, very accurately, the commands for on the monitor by rolling it on a smooth
various jobs. Definitely, most people found surface or a mouse pad. Positioning the
it inconvenient. But not any more. Today as cursor on to a particular icon, or a title
one switches on one's PC, one is in a list, and clicking the button on the
welcomed by a colourful graphic display mouse is a sufficient command to open the
on the monitor. In fact, most often one can required file.
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ten million transistors, each connected to
The most enigmatic part of a computer is many others through microscopic lines of
the CPU, or the brain of the computer. It is aluminium that act as wires. The last few
made up of many ICs (Integrated Circuits), generations of PCs are known by the
and other kinds of components that are name of the microprocessor like 386, 486,
Pentium, Celeron, Xeon, Athlon, Cyrix.found in computers only.
A microprocessor is the central control One feature that distinguishes one kind
area of the computer. It is a microscopic of microprocessor from another is the
circuit of a silicon chip and is made up of 'clock speed', a built-in clock, that sets the
silicon, aluminium or copper and plastic. pace for all activities inside it. The clock
It contains thousands of electronic devices speed is measured in cycles per second
known as transistors on a thin slice of
silicon only about six millimetres square in
size! It has many electronic switches inside
it that helps it to do its task by stopping or
allowing the electric current through
them. A transistor is the basic unit of each
such switch. It is through selective
switching 'on' and 'off' of transistors that
a microprocessor acts as the brain of
a computer. A microprocessor used In the
present generation of computers (say
a P-4 computer) is made up of as many as11I1I1I1I1II1111111 I 1 1 I I 1 1 I I 101 I 1 101 I
(a unit also called the Hertz or Hz). You will
come across words like MHz or GHz in the
advertisements for computers in news­
papers and magazines. The clock speed
of the latest brand of microprocessors isIntegrated Circuit
above a billion Hertz.ICs are an essential component of any
electronic device. An IC often looks like a small There are several kinds of memory: the
piece of plastic with many metallic legs. Inside basic memory, the short-term memory and
an IC, there is a complex electronic circuit made the long-term memory in a computer like
up of different kinds of components­
in our brain. Although we do not have
transistors, resistors and capacitors. They are all
a unit that measures the memory of ourconnected to each other through extremely thin
brain, we do have a unit for the memory oflines of copper and are engraved on a tiny chip
a computer. It is known as byte.of silicon.
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users often say one MB rather than the
The smallest unit of the memory of 1024 kilobytes or one GB instead of saying
a computer is a bit (an acronym for binary one billion bytes. K stands for kilo or
digit). A bit is a single transistor device in thousand. To be exact K stands for 1024
a computer, which is akin to a light bulb. bytes. Very soon, when you grow up a bit,
It has only two possible states, 'on' (often you will encounter the term TB (Terabytes,
indicated by the numeral 1) or 'off' that is, a trillion bytes) too.
(indicated by 0). To store or convey more Corresponding to the various kinds of
information, bits are organized into larger memory in our brain, computers have
units called bytes-the commonly used ROM (the basic memory), RAM (short-term
unit of information in a computer. Each byte memory) and the Disk Drive (long-term
contains 8 bits and can represent only memory).
a single character or command. A brief Off On Off Off On Off On Off
letter to your friend may require just a few
thousand bytes, whereas to store
a postcard size colour photograph, it may
require several million bytes.
The terms, KB (kilobytes), MB
o 1 o 0 1 0 1 o(megabytes) or GB (gigabytes) one often
Character Byte Character Bytecomes across in advertisements for
(8 bits) (8 bits)computers, are more convenient units. Just
A - 01000001 0 00000000-
as a businessman finds it to talk B - 01000010 1 - 00000001
01000011 2 01000010C - -In terms of lakhs and crores, computer
0 01000100 3 00000011- -
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