CS 1428 Foundations of Computer Science I

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  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.

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

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 5

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 6

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, 2 bits states CS 1308 – Computer Literacy and the Internet 7

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.

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 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

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?

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

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…?

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…?

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

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?