The von Neumann Computer. IT 3123 Hardware and Software Concepts. One Model of Computing. Main Memory. Peripherals. One Model of Computing

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1 IT 3123 Hardware and Software Concepts Computer Peripherals February 22 The von Neumann Computer CPU PC IR Accumulator MAR MDR Command I-O Notice: This session is being recorded. Copyright 2005 by Bob Brown 2 Main Memory Main Memory Main memory is short-term storage Holds programs and data for running processes Does not (usually) hold data for processes that are not running Contents are lost when power is turned off. Is not generally thought of as storage. One Model of Computing Image copyright John Wiley and Sons CPU and Memory Long-term storage of programs and data 3 4 One Model of Computing Image copyright John Wiley and Sons Transfer to and from storage is I-O Peripherals Devices that are separate from the basic computer Not the CPU, memory, power supply Classified as input, output, and storage Connect via Ports parallel, USB, serial, Firewire Interface to system bus SCSI, IDE, PCMCIA, SATA 5 6 1

2 Storage Speed Measured by access time and data transfer rate Access time: average time it takes a computer to locate data and read it millisecond = one-thousandth h of a second Data transfer rate: amount of data that moves per second Hierarchy of Storage Device Access Times Transfer Rate CPU Registers ½ nanosecond Cache memory 5-30 ns Main memory ns Hard disk ms. 600k-6m/sec Floppy disk 100 ms k/sec CD-ROM ms 500k-4m/ sec Tape ½ sec up 11m /sec 7 8 Sequential and Direct Access Sequential access: You must pass over all prior data to reach a given piece of data; tape devices (music and computer) are sequential access. Direct access: Access to any block of data on the medium takes about as long as access to any other; disks, CD-ROM, and DVD are direct access. Compare direct access to random access. 9 Direct Access Devices Hard disks Floppy disks Optical disks (CD, DVD) when reading. 10 Sequential Access Devices Tapes (many sizes, formats) Optical devices (CD-ROM, DVD) when writing. Magnetic (Hard) Disks

3 13 Magnetic Disk Geometry A: Track B: Sector (pie-shaped wedge) C: Block (sometimes also called a sector) D: Cluster (allocation unit consisting of several blocks) Magnetic Disk Terminology Platter a circular piece of metal coated on both sides with magnetic recording material Track circle around the disk Cylinder collection of tracks consisting of the same track on all platters Block amount of data held in a sector (sometimes also called a sector.) Sector an arc of a track Head reads/writes data off the disk 14 Disk Rotation The number of bits is the same for every track. The recording density must be greater toward the center of the disk. Disk rotation speed is constant regardless of the position of the heads: constant angular velocity. Rotation speeds of 3,600 to 15,000 RPM (floppy disks, about 360 RPM) 15 Reading from Disk Seek time: time required to move from one track to another Rotational latency: time required for disk to rotate to beginning of correct sector Transfer time: time required to transfer a block of data to the disk controller buffer 16 Disk Access Time Seek Time: average time to move from one track to another Rotational Latency Time: time to rotate to the beginning of the sector, average = ½ * 1/rotational ti speed Transfer Time: 1/(# of sectors * rotational speed) Total Time to access a disk block: Seek Time + Latency Time + Transfer Time 17 Disk Block Formats Inter-block gap Header (synchronization, error control) Data Next gap 18 3

4 Zoned Disks Modern disks have more sectors per track at the outer edge than near the center. A typical disk might have a dozen or so such zones. About Head Crashes Disk heads fly a few thousandths of an inch from the disk surface on an air bearing created by the spinning disk. The disk is moving very fast. If the head touches the disk, it can abrade the magnetic material; this is a head crash. The magnetic material is destroyed, and the debris causes other head crashes Stopping and Starting When the disk is stopped, the heads are parked in a special area of the platter called a landing zone. When the disk is started, the heads are kept in the landing zone until the disk is spinning fast enough for the heads to fly. When the disk is turned off, the heads are returned to the landing zone as the platters slow down. Redundant Disks If redundant (duplicative) data are stored on two or more disks, the failure of any single disk will not cause data loss. RAID = redundant array of inexpensive disks. Levels of RAID RAID 1: Mirrored disk volumes RAID 5: Bits of each data word duplicated across three or more drives RAID 5 (1,2) Image Courtesy of Sun Microsystems Networked Storage File servers: general-purpose computers with software that makes their disks accessible over the network Network Attached Storage (NAS): Special-purpose appliances that t work like file servers Storage Attachment Network (SAN) large arrays of disks are apportioned to many CPUs. Attachment is fiber or fast Ethernet. 24 4

5 Optical Storage Bits stored by burning pits in a reflective surface with a medium-power laser. Reading is accomplished with a low-power laser. If the light is reflected, no pit is present. (The areas that are not pits are called lands. ) CD-ROM A single, spiral track (vs. many concentric circular tracks on a disk.) Constant linear velocity; rotational speed changes to maintain constant bit rate. (Mostly for older drives.) CD and DVD Both are optical storage. Read-Write Modes Read-only Write once, read many (WORM) Read-write CD: MB DVD: 4+ GB per layer Up to 2 layers per side Total of 17 GB Magnetic Tape Image Copyright 2002 Jones and Bartlett Publishers Magnetic Tape Offline storage Archival purposes Disaster recovery Tape Cartridges tracks (side by side) Read serially DAT digital audio tape (small size) Smart tapes Tape libraries and auto-loaders 29 Displays Pixel: A single colored dot on the screen, contraction of picture element. Also called pel. Resolution: Pixels on the screen 480 x x x x

6 How many pixels? Picture Size 640 x 480 = 307, x 1024 = 1,310,720 How many bits per pixel? 24 bits x 1,310,720 = 31,457,280 (about 8MB) Screen Size Screen size: measured diagonally Resolution: minimum identifiable pixel size Aspect ratio: x pixels to y pixels 4:3 on most PCs 16:9 on high definition displays Colors Additive colors: red, green, blue Number of bits/color determines how many colors can be displayed 4 bits = = 4,096 colors (2 12 ) 8 bits = =16.7 million colors (2 24 ) 33 LCD Displays Fluorescent light panel 3 color cells per pixel Operation 1 st filter polarizes light in a specific direction Electric charge rotates t molecules l in liquid id crystal cells proportional to the strength of colors, changing polarization Color filters only let through red, green, and blue light Final filter lets through the brightness of light proportional to the polarization twist 34 LCD Displays LCD Displays Active matrix One transistor per cell More expensive Brighter picture Passive matrix One transistor per row or column Each cell is lit in succession Display is dimmer since pixels are lit less frequently

7 Printers Dots vs. pixels dpi vs pixels per inch Dots are on or off, pixels have intensities Types Inkjet squirts heated droplets of ink Laser xerographic imaging Thermal wax transfer Dye Sublimation } Color technologies Older technologies Dot matrix, fully-formed characters Creating a Gray Scale Laser Printer Operation Dots of laser light are beamed onto a drum Drum becomes electrically charged Drum passes through toner which then sticks to the electrically charged places Electrically charged paper is fed toward the drum Toner is transferred from the drum to the paper The fusing system heats and melts the toner onto the paper A corona wire resets the electrical charge on the drum 39 Other Peripherals Scanners Flatbed, sheet-fed, hand-held Light is reflected off the sheet of paper User Input Devices Keyboard, mouse, light pens, graphics tablets 40 Communications and Networking MODEM DSL Cable modem Ethernet High-speed networking Wireless networking MODEM MOdulator/DEModulator: Alters (modulates) an audible signal to encode digital information Operates over the dial network; the phone line is busy when in use for data. Theoretical maximum speed: 64 kbps Practical maximum: 52 kbps

8 Digital Subscriber Line Both analog (low frequency) and digital (high frequency) signals on one pair of wires Network connection is always on. Phone conversations are possible while network traffic is present Speeds to 6+ mbps Cable Modem One or more channels on the cable are devoted to data Speeds up to 6 or more mbps Multiple subscribers on one connection (a possible security problem) Data Voice Multiplexor Splitter Subscriber Premises Telephone Office ` Ethernet A local-area networking technology 10, 100, or 1000 mbps Multiple-access (more than two devices on the same wire) CSMA/CD Switched access: each device is connected to a switch and isolated from other devices. High-Speed Networking Billions of bits per second Fiber optic cable ATM or SONET protocols Wave division multiplexing National Lambda Rail (up to 320 billion bits per second!) Wireless Networking Local Area IEEE standards 2.4 GHz or 5 GHz microwave Two to 50+ mbps Short distances Possible security concerns Wide area Cellular infrastructure Speeds around 256 kbps Possible security concerns 47 Broadband and Baseband Baseband: only one signal travels on the communication medium. (It could be a very fast signal!) Broadband: Two or more independent signals, like channels h l on television tl ii cable systems. Broadband is now used to mean fast even when only one signal is involved. 48 8

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