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What is a Computer?

CS 1428 Foundations of Computer Science I. What is a Computer?. Two Main Components. Hardware Physical media that uses electrical current to process instructions. Software Instructions written by humans that tell the computer what to do. The Modern Computer. The Stored-Program Model

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What is a Computer?

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  1. CS 1428 Foundations of Computer Science I What is a Computer?

  2. Two Main Components • Hardware • Physical media that uses electrical current to process instructions. • Software • Instructions written by humans that tell the computer what to do.

  3. The Modern Computer • The Stored-Program Model • Invented by John von Neumann • Digital Information • Memory • Processor • Input/Output • Secondary Storage • We will revisit this model in much more detail later in the semester.

  4. Data Bus Memory (RAM) Organization of a von Neumann Machine – (almost every modern computer) Input/Output I/O Central Processing Unit (CPU) Secondary Storage

  5. Information in the Real World • Information that we gather through our senses is primarily in waves and typically analog. • Light • Sound • Temperature • Etc. • Information can be quantified down to the atom • That’s a lot of information! CS 1308 – Computer Literacy and the Internet

  6. Information in the Computer World • Information in the computer world is digital. • On/Off • Fully Charged – Fully Discharged • Magnetized – Demagnetized • Computer information is binary. • 0 – Off • 1 – On • Detecting Voltage Levels • Why not 10 levels? • Would be unreliable • Not enough difference between states CS 1308 – Computer Literacy and the Internet

  7. Bits, Bytes, and so on • A bit is one 0 or 1 • Short for “binary digit” • A byte is a collection of 8 bits • They named it “byte” instead of “bite” so you couldn’t easily mess up the spelling and confuse it with “bit”. • Anybody know what half a byte is called? • The number of bits we have will determine how much information we can store. (VERY IMPORTANT) • 1 bit, on or off (two states) • 2 bits, four different states (00, 01, 10, 11) • 3 bits, eight states • In general, 2bits states CS 1308 – Computer Literacy and the Internet

  8. What is Data? • Any useful input or output from the computer • Documents that you are working on • .doc, .xls, .pdf • Music • .mp3 • Pictures • .jpg, .gif • Text • The quick Brown Fox… • Numbers • 42, 3.14 • Readings from sensors • Others…? • All of these are encoded in a consistent binary format so they can be shared between computers and users.

  9. What is an Instruction? • Computers rely on very simple instructions given to them by programmers to accomplish tasks. • Assembly Language (written by humans) • LOAD R1, #42 • JUMP R2 • ADD R1, R2 • These instructions are translated to Machine Language • Computers only understand ones and zeros • 1010001001010011 • 1000111101001111 • 1010010010100011 • Programs consist of millions of these instructions • Machine language is different for each processor • That is why Mac programs won’t run on a PC

  10. Random Access Memory (RAM) • The programs (instructions) and data are stored in the Random Access Memory (RAM) for use by the Central Processing Unit (CPU). • RAM loses it’s memory when the power goes off so we store information and programs more permanently on Secondary Storage Devices (hard drives, flash drives, etc.). • Data and instructions are Fetched from the RAM and used by the CPU to perform tasks. • RAM is finite. • What implications does this have for real numbers?

  11. Central Processing Unit (CPU) • The CPU uses instructions to move data around in the computer and to produce output. • The CPU has a simple task. Follow the Execution Cycle over and over again, very quickly. • Fetch an instruction • Decode the instruction • Execute the instruction

  12. Input/Output (I/O) • Every useful computer creates some kind of output. • Most computers use input data of some kind to produce the output. • Garbage in = Garbage out • Bad data leads to useless results. • Devices • Input • Keyboard • Mouse • Others…? • Output • Monitors • Speakers • Others…?

  13. Secondary Storage • The memory in RAM goes away when the power is shut off. • Volatile • Programs and data are stored more permanently on secondary storage devices. • Contain much more space than RAM. • Hard Drives • USB Drives • DVD • CD • Others…?

  14. Data Bus Memory (RAM) Organization of a von Neumann Machine – (almost every modern computer) Input/Output I/O Central Processing Unit (CPU) Secondary Storage

  15. Quiz • Which of the following are a computer? • How can we tell? • Does it have a processor? • Does it have memory to store data and/or a program? • Does it use input or create output?

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