Laboratorio di Calcolo II

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Laboratorio di Calcolo II

• Obbiettivo insegnarvi a scrivere programmi in
  c
• 2 ore/settimana di lezione in aula
• 4 ore/settimana di esercitazioni personali al
  computer
• Esercitazioni per studenti lavoratori il sabato
  mattina
• Fondamentale la partecipazione alle esercitazioni
• Lesame consiste nello scrivere un programma e
  nel discuterlo con il docente

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Docente

• Fabrizio Bianchi
• Tel. [phone]
• E-mail bianchi_at_to.infn.it
• URL www.to.infn.it/bianchi

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Testo e Materiale

• Testo consigliato C, How to Program, Deitel
  Deitel, 4E, Prentice Hall
• Esiste la traduzione italiana della terza
  edizione
• Trasparenze www.to.infn.it/bianchi/LaboratorioCa
  lcoloII/ lezxy.ppt formato
  powerpoint
  lezxy.pdf formato pdf (consigliato per la
  stampa)
• Raccomando di partecipare a lezioni ed
  esercitazioni con copia delle trasparenze
  

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What is Programming?

• A sequence of statements that instruct a computer
  in how to solve a problem is called a program.
• The act of designing, writing and maintaining a
  program is called programming.
• People who write programs are called programmers.

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What kinds of statementsdo computers understand?

• A computer only understands machine
  language statements.
• A machine language statement is a sequence of
  ones and zeros that cause the computer to perform
  a particular action, such as add, subtract,
  multiply, ...

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Machine Language (ML)

• ML statements are stored in a computers memory,
  which is a sequence of switches.
• For convenience of representation, an
  on switch is represented by 1, and an
  off switch is represented by 0.
• ML thus appears to be binary (base-2)
• 0010111010110101

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Early Computers

• ... required a programmer to write in ML...
• Easy to make mistakes!
• Such mistakes are hard to find!
• Not portable -- only runs on one kind of machine!
• Programming was very difficult!

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A Bright Idea

• Devise a set of abbreviations (mnemonics)
  corresponding to the ML statements, plus a
  program to translate them into ML.
• The abbreviations are an assembly language, and
  the program is called an assembler.

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Assembly Languages

• Allowed a programmer to use mnemonics, which were
  more natural than binary.
• Much easier to read programs
• Much easier to find and fix mistakes
• Still not portable to different machines

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High Level Languages

• Devise a set of statements that are close to
  human language (if, while, do, ...), plus a
  program to translate them into ML.
• The set of statements is called a high level
  language (HLL) and the program is called a
  compiler.

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HLL Compilers

• Where an assembler translates one mnemonic into
  one ML statement, a
  HLL compiler translates one HLL statement into
  multiple ML statements.

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HLLs

• High level languages (like C) are
• Much easier to read programs
• Much easier to find and fix mistakes
• Portable from one machine to another
  (so long as they keep to the language standard).

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Objectives in Programming

• A program should solve a problem
• correctly (it actually solves the problem)
• efficiently (without wasting time or space)
• readably (understandable by another person)
• in a user-friendly fashion
  (in a way that is easy for its user to use).

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Summary

• There are levels to computer languages
• ML consists of low level binary statements,
  that is hard to read, write, and not portable.
• Assembly uses medium level mnemonics easier to
  read/write, but not portable.
• C is a high level language that is even
  easier to read/write, and portable.

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Computer Organization
Hardware and Software
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Computing Systems

• Computers have two kinds of components
• Hardware, consisting of its physical devices
  (CPU, memory, bus, storage devices, ...)
• Software, consisting of the programs it has
  (Operating system, applications, utilities, ...)

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Hardware CPU

• Central Processing Unit (CPU)
• the brain of the machine
• location of circuitry that performs arithmetic
  and logical ML statements
• measurement speed (roughly) in megahertz
  (millions of clock-ticks per second)
• examples Intel Pentium, AMD K6, Motorola
  PowerPC, Sun SPARC,

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Hardware RAM

• Random Access Memory (RAM)
• main memory, which is fast, but volatile...
• analogous to a persons short-term memory.
• many tiny on-off switches for convenience
• on is represented by 1, off by 0.
• each switch is called a binary digit, or bit.
• 8 bits is called a byte.
• 210 bytes 1024 bytes is called a kilobyte (1K)
• 220 bytes is called a megabyte (1M).

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Hardware (Disk)

• Secondary Memory (Disk)
• Stable storage using magnetic or optical media.
• Analogous to a persons long-term memory.
• Slower to access than RAM.
• Examples
• floppy disk (measured in kilobytes)
• hard disk (measured in gigabytes (230 bytes))
• CD-ROM (measured in megabytes), ...

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Hardware the Bus

• The Bus
• Connects CPU to other hardware devices.
• Analogous to a persons spinal cord.
• Speed measured in megahertz (like the CPU), but
  typically much slower than the CPU...
• The bottleneck in most of todays PCs.

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Hardware Cache

• While accessing RAM is faster than accessing
  secondary memory, it is still quite slow,
  relative to the rate at which the CPU runs.
• To circumvent this problem, most systems add a
  fast cache memory to the CPU, to store recently
  used instructions and data.
• (Assumption Since such instructions/data were
  needed recently, they will be needed again in the
  near future.)

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Hardware Summary

• Putting the pieces together

Programs are stored (long-term) in secondary
memory, and loaded into main memory to run, from
which the CPU retrieves and executes their
statements.
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Software OS

• The operating system (OS) is loaded from
  secondary memory into main memory when the
  computer is turned on, and remains in memory
  until the computer is turned off.

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Software OS

• The OS acts as the manager of the system,
  making sure that each hardware device interacts
  smoothly with the others.
• It also provides the interface by which the user
  interacts with the computer, and awaits user
  input if no application is running.
• Examples MacOS, Windows-98, Windows-NT, UNIX,
  Linux, Solaris, ...

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Software Applications

• Applications are non-OS programs that perform
  some useful task, including word
  processors, spreadsheets, databases, web
  browsers, C compilers, ...
• Example C compilers/environments
• CodeWarrior (MacOS, Win95, WinNT, Solaris)
• GNU C (UNIX, Linux)
• Turbo/Borland C (Win95, WinNT)
• Visual C (Win95, WinNT)

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Software User Programs

• Programs that are neither OS programs nor
  applications are called user programs.
• User programs are what youll be writing in this
  course.

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Putting it all together

• Programs and applications that are not running
  are stored on disk.

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Putting it all together

• When you launch a program, the OS controls the
  CPU and loads the program from disk to RAM.

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Putting it all together

• The OS then relinquishes the CPU to the program,
  which begins to run.

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The Fetch-Execute Cycle

• As the program runs, it repeatedly fetches the
  next instruction (from memory/cache), executes
  it, and stores any results back to memory.

Disk
RAM
CPU
Cache
OS
App
App
App
Bus
Thats all a computer does fetch-execute-store,
millions of times each second!
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Summary

• A computer has two kinds of components
• Hardware its CPU, RAM, Disk(s), ...
• Software, its OS, Applications, and User Programs.