CS 140 Introduction to Computing & Computer Technology. Computing Components

CS 140 Introduction to Computing & Computer Technology Computing Components

We ve looked at the elementary building blocks of computers transistors, gates, and circuits OK, but how do computers really work? Gates and circuits operate on the most elemental of data items binary 0s and 1s People reason with more complex units of information decimal numbers, character strings, instructions, etc. To understand how computers process these more complex pieces of information we must look at higher-level components than gates and circuits We must study computers as collections of functional units or subsystems that perform operations such as instruction processing information storage computation data transfer

Computer Components Consider the following ad: Insatavialion 640 Laptop Exceptional Performance and Portability Intel Core 2 Duo (2.66GHz/1066Mhz FSB/6MB cache) 15.6 High Definition (1080p) LED Backlit LCD Display (1366 x 768) 512MB ATI Mobility Radeon Graphics Built-in 2.0MP Web Camera 4GB Shared Dual Channel DDR2 at 800MHz 500GB SATA Hard Drive at 5400RPM 8X Slot Load DL DVD+/- RW Drive 802.11 a/g/n and Bluetooth 3.0 85 WHr Lithium Ion Battery (2) USB 2.0, HDMI, 15-pin VGA, Ethernet 10/100/1000, IEEE 1394 Firewire, Express Card, Audio line-in, line-out, mic-in 14.8W X 1.2H X 10.1D, 5.6 lbs Microsoft0 Windows 7 Professional Microsoft Office Home and Student 2007 36-Month subscription to McAfee Security Center Anti-virus 3

Virtually every computer in use today is based on a single design Analogous to automotive technology: although a pickup truck looks very different from a Ferrari, they are both constructed using the same basic technology a gasoline-powered internal combustion engine turning an axle that turns the wheels Differences are not basic theoretical differences but variations on a theme» bigger engine» larger carrying capacity» more luxurious interior

Structure and organization of virtually all modern computers are based on a single theoretical model of computer design called the Von Neumann architecture after John Von Neumann, who first proposed it in 1946

The von Neumann architecture identifies 3 essential components: Input/Output Devices (I/O) allow the user to interact with the computer Memory stores information to be processed as well as programs (instructions specifying the steps necessary to complete specific tasks) Central Processing Unit (CPU) carries out the instructions to process information

Stored program concept A program can be encoded as bit patterns and stored in main memory. From there, the CPU can then extract the instructions and execute them

The CPU is comprised of several subunits Arithmetic Logic Unit (ALU): circuitry that performs the actual operations on data (e.g., addition, subtraction) Registers: memory locations built into the CPU (to provide fast access) Control Unit: circuitry in charge of fetching data and instructions from main memory, as well as controlling the flow of data between registers and the ALU

CPU clock Operation of digital hardware governed by a constantrate clock Clock (cycles) Data transfer and computation Clock period Clock frequency (rate): cycles per second E.g., 4.0GHz = 4000MHz = 4.0 10 9 Hz

Combinational logic transforms data during clock cycles Between clock edges Longest delay determines clock period Performance improved by Reducing number of clock cycles Increasing clock rate Hardware designer must often trade off clock rate against cycle count

Bus Flow of Information A set of wires that connect all major sections Figure 5.2 Data flow through a von Neumann architecture 13

Memory A collection of cells, each with a unique physical address; both addresses and contents are in binary Memory

RAM and ROM Random Access Memory (RAM) Memory in which each location can be accessed and changed Read Only Memory (ROM) Memory in which each location can be accessed but not changed RAM is volatile, ROM is not What does volatile mean? 16

Von Neumann simply assumed that whenever the computer needed an instruction or a piece of data, it would get it from RAM As computers became faster, designers noticed that, more and more, the processor was sitting idle waiting for data or instructions to arrive Processors were executing instructions so quickly that memory access was becoming a bottleneck To solve this problem, designers needed to decrease memory access time to make it comparable with the time needed to carry out an instruction. But extremely fast memory is also quite expensive

Caching Information in use copied from slower to faster storage temporarily Faster storage (cache) checked first to determine if information is there

Caching Analogy You are going to do some research on a particular topic. Thus, you go to the library and look for the a shelve that contains books on that particular topic You pick up a book from the shelve, find a chair, seat and start reading

You find a reference to another book on the same topic that you are also interested in reading. Thus, you stand up, go to the same shelve, leave the first book and pick up the other book Then, you go back to the chair and start reading the second book Later on you realize that you want to read the first book once again (or another related book). Thus, you repeat the same process (i.e., go to the shelve to find it)

Suppose that instead of taking just one book from the shelve, you take 10 books on the same topic. Then, you find a table with a chair, put the 10 books on the table, sit there and start reading one of the books If you need another related book, there is a good chance that it is on your table so you don t have to go to the shelve to get it. Also, you can leave the first book on the table and there is a good chance that you will be needing it again later

Designers observed that when a program fetches a piece of data or an instruction, there is a high likelihood that It will access that same instruction or piece of data in the very near future It will access the instructions or data that are located near this one This observation is called the principle of locality

Another good analogy to cache memory is a home refrigerator. Why?

Ideally, we want programs and data to reside in main memory permanently Main memory is usually too small Main memory is volatile loses contents on power loss Secondary storage holds large quantities of data, permanently Magnetic disk is the most common secondary-storage device

Read/Write Head Side View

Transfer rate is rate at which data flows between drive and computer Positioning time (random-access time) is time to move disk arm to desired cylinder (seek time) and time for desired sector to rotate under the disk head (rotational latency) Distance between disk surface and read-write head is less than 0.1 microns (1 micron = 1 millionth of a meter). A human hair is 50 microns Head crash results from disk head making contact with the disk surface That s bad

Input/Output Units Input Unit A device through which data and programs from the outside world are entered into the computer; Can you name three? Output unit A device through which results stored in the computer memory are made available to the outside world Can you name two? 31