1. 7-1 Communicating with the Computer How do programs get in to memory in the first place? Input/Output (I/O): –Refers to the process of getting information into and out of the computer. computer cp u memo ry input device(s) output device(s) peripheral devices

2. 7-2 I / O Peripheral device: a piece of hardware that is outside the main computer. –“Clearly” peripheral devices are necessary to use our computer in any meaningful way... Input units: –Computer hardware devices that receive input and bring that input into the computer –What are some input devices? Output units: –Computer hardware that caries information out of the computer (i.e., produce output) –What are some output devices?

3. 7-3 Input Devices Input devices: –Keyboard –Mouse –Scanner –Digital camera –Video camera/capture device –Temperature sensor –Pressure sensor –How does a keyboard really work? You press a key (which is really a switch) The ASCII code of the key you’ve pressed is sent into the computer (Voltage is set on the wires according to the key you’ve pressed)

4. 7-4 Input Devices How does a mouse work (physically) ? (the buttons are just switches) A little ball sits inside the mouse The ball rolls against three rollers, two of the rollers act as “rotary switches” so they know when they’ve been moved When the mouse moves, the ball rolls and the rotary switches are moved as well –One rotor is aligned to measure left and right movement –The other is aligned to measure up and down movement The changes in X and Y coordinate updates are sent to the computer as binary numbers –A program needs to be running on the computer that knows what to do with mouse updates

5. 7-5 Output Devices –Output devices: Monitor / Video card Printer Sound card Network card Robotic arm

6. 7-6 Display Technologies Hi-resolution displays come in two types: –Each takes an input signal and creates a visible image Cathode ray tube (CRT) - Streams of electrons make phosphors glow on a large vacuum tube. –Monitor Liquid crystal display (LCD) - A flat panel display that uses crystals to let varying amounts of different colored light to pass through it. –Developed primarily for portable computers. –Panel How does a monitor really work –i.e., how does the image get there?

7. 7-7 Video Display –How does a monitor really work –how does the image get there? The video card or graphics card sends video signals to the monitor The video card has it’s own memory and CPU –The Graphics Processing Unit (GPU) receives instructions (from the CPU) to draw an image (bitmap) to the display –The image data (bitmap) will be copied from primary memory to video memory (VRAM) –The video signal is sent periodically ensuring that the monitor is displaying the video image described in the VRAM contents this is complicated, but the video card takes care of everything for us Let’s consider a much simpler output device -- –Daisy wheel printers »“letter quality” printer

8. 7-8 “Other” Devices There are other devices that we have yet to mention that don’t fit nicely into either “input devices” or “output devices” –Floppy drives, –Hard disks –CD-ROM drives –DVD-ROM drives –CD-RW/DVD-RW drives They are input devices to our computer, but can also be output devices. –There’s something else weird about them, consider the type of the input they process –We consider “traditional” input devices those that deal with original data. –And define a classification for devices that handle previously stored data.

9. 7-9 Data Sources Computer data can be: –Original data: Data being introduced to a computing system for the first time. The input device directly samples physical things in the world (printed text, pictures, sound, and other common types of information) and converts them to binary for the computer Think: non-binary inputs that need to be converted Examples: ? –Digitizing: The process of taking an image, audio recording or any other analog data and converting it to a binary format for the computer. Allows our computer (and programs) to represent and manipulate “analog data”

10. 7-10 Data Sources Computer data can be : –Previously stored data or information: Data that has already been processed by a computer and is being stored for later use. The input devices directly reads binary data (the data has already been converted to binary). The binary form of the data is useful only to a computer –Using a CDR as a drink coaster doesn’t count as using binary data Think: Already converted to binary Examples: –music CDs? –It would be useful to have “previously stored data”-devices that can both read and write binary data

11. 7-11 Storage Devices Storage Devices – “Secondary Memory” –used by a computer to Write binary information (store) Read binary information as needed (retrieve) –compared to primary memory, it’s slower but less expensive slower means it takes more time to get a bit from the device –“Secondary” with respect to the Von Neumann model Technically a kind of memory –Can be used to manipulate bits But calling it memory is really incorrect –By Von Neumann’s definition, it is secondary – not required –Take bits from memory and output them to a device »Move papers from desk to cabinet –Take bits from a device and put them in memory »Or move from filing cabinet to desk

12. 7-12 Storage Devices Literally, storage devices are input and output devices –Remember, the CPU can only take instructions from primary memory If we have a program to run on a storage device compared to directly in memory –These devices are slower to access, so it may take longer to “find” or “get” our bits –Then, we’ll need to copy the instructions into memory before we can run them If we want to put results on a storage device we’ll need to copy them from memory –So, if primary memory were cheap enough, would we still need storage devices? Yes! Remember, memory contents are lost when power is removed from the computer. This is not the case with storage devices. How is a storage device able to “keep” it’s bits where as RAM can not?

13. 7-13 How do we really store data? Storage Technologies for Binary Information: –Electronic –Magnetic –Optical

14. 7-14 Device Storage Electronic Circuits –Most expensive of the three forms for storing binary information. –A flip-flop circuit has either one electronic status or the other. It is said to flip-flop from one to the other. –Electronic circuits come in two forms: Permanent Non-permanent

15. 7-15 Device Storage Magnetic Technology –Very inexpensive form of storage –A special surface can hold magnetic information (+/-) Tiny spots on the surface are magnetized to represent 1s and 0s It has a magnetic sensing “head” moves over the surface Can perform non-destructive reading Can destructively write to a surface (over-writing existing 1s and 0s) –Examples: »Floppy Drives »Hard Drives »Zip Drive »Tape Drives

16. 7-16 How the disk drive really works … 0111001011100 ( not to scale :-P ) The disk is covered in magnetic 1s and 0s –The disk spins –The head moves back and forth, reading or writing 1s and 0s from/to the different areas on the disk. Like a record player, the head only needs to go in a straight line across the disk, and the disc will spin under it Seek time: time it takes to find the desired bit on the physical device. –complicated, but the hard disk takes care of all of this for us Floppy drives, Hard drives... –How would a tape drive work?

17. 7-17 Device Storage Optical –“Slower” than magnetic media, price is on par –Uses lasers to “read” the binary information from a surface. –Millions of tiny holes are “burned” into the surface of the disc. The surface of re-writable optical media is a chemical that changes and reforms when hit with the “low-power” laser head The laser “burns” the chemical  hence “burning” a CD The holes are interpreted as 1s. The absence of holes are interpreted as 0s. »So, this looks just like before, but instead of a magnetic head, we have a laser head to read the gapping as 0s & 1s »This is the mechanism for CDs, DVDs, CDRs, Laserdiscs, etc

18. 7-18 Optical Storage Devices Optical Disks: CD-ROM, DVD, etc –CD-ROM (Compact Disc - Read Only Memory) By its definition, CD-ROM is Read Only. –types of CDs: »CD-R (Compact Disc - Recordable) »CD-RW (Compact Disc - Rewritable) –DVD, DVD-R, DVD+R, DVD-RW, DVD+RW, DVD-R9/DL DVD really didn't stand for anything when it was introduced, yet there are two often used names –Digital Video Disc and Digital Versatile Disc –Neither is “official” Writing to an Optical device must be done “in one sitting” as opposed to magnetic media which is easy to change “on the fly”

19. 7-19 Characterizing Capacity Capacity - The amount of information that can be stored on the medium. UnitDescriptionApproximate Size 1 bit1 binary digit 1 nibble4 bits 1 byte8 bits1 character (ASCII) 1 kilobyte1,024 bytes  1/2 page, double spaced 1 megabyte1,048,576 bytes  500,000 pages 1 million bytes 1 gigabyte1,073,741,824 bytes  5 million pages 1 billion bytes 1 terabyte1 trillion bytes  5 billion pages

20. 7-20 Capacity continued How much storage capacity is needed for… –One keystroke on a keyboard.1 Byte (8 bits) –One page single-spaced document.4.0 KB –One second of uncompressed (WAV) sound.176 KB –One hour of uncompressed WAV sound619MB –One hour of MPEG2 video~2.3GB How much data can be stored on… –One inch of 1/2 in. wide magnetic tape.4 K –One 3 1/2” floppy disk, high density.1.4 MB –One Compact Disc.700 MB –One DVD-R.~4.3 GB –One Dual-Layer DVD. ~9 GB

21. 7-21 Characterizing Devices Type of Access Sequential - Obtained by proceeding through the storage medium from the beginning until the designated area is reached (as in magnetic tape). Random Access – “Direct” access (as in floppy and hard disks). Type of Access directly influences speed –Seek times are longer for sequential access devices  –Sequential devices are slower than random access devices

22. 7-22 Characterizing Devices Speed (Access time) - How fast information (bits) can be taken from or stored to the device. –Electronic circuits: Fastest to access. 40 billionths of a second. –Floppy disks: Very slow in comparison. Takes up to 1/2 second to reach full speed before access is even possible. Why? Have to spin the disk and get the head into the right place. Then the reading of magnetic charge is converted into a 1 or 0 Why do we tolerate slow devices? –Cost –Portability?