Computer Systems Figure 5.1 The von Neumann architecture

CPU

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

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?

Secondary Storage Devices Why is it necessary to have secondary storage devices? Can you name some of these devices?

Magnetic Tape The first truly mass auxiliary storage device was the magnetic tape drive Tape drives have a major problem; can you describe it? Figure 5.4 A magnetic tape

Magnetic Disks History Floppy disks (Why "floppy"?) " in diameter " late 1970, 5 1/2" 80’s, 3 1/2” now near extinction Zip, removable drives Tracks near center are more densely packed Why?

Magnetic Disks Eric Gaba, Wikimedia Commons user Sting

… Amazing… “As an analogy, a magnetic head slider flying over a disk surface with a flying height of 25 nm with a relative speed of 20 meters/second is equivalent to an aircraft flying at a physical spacing of 0.2 µm at 900 kilometers/hour. This is what a disk drive experiences during its operation.” Magnetic Storage Systems Beyond 2000, George C. Hadjipanayis, p. 487

Magnetic Disks Seek time Time it takes for read/write head to be over right track Latency Time it takes for sector to be in position Access time Access time Sum of seek time and latency.

RAID “redundant array of inexpensive disks” “redundant array of inexpensive disks” multiple disks look like one drive to OS multiple disks look like one drive to OS uses: uses: –mirroring –striping –error detection

Flash memory Flash memory Non-volatile limited number of read/write cycles (300K) better shock-resistance than HD; faster access time future: flash drives only?

Compact Disks CD A compact disk that uses a laser to read information stored optically on a plastic disk; data is evenly distributed around track CD-ROM read-only memory CD-DA digital audio CD-WORM write once, read many RW or RAM both read from and written to DVD Digital Versatile Disk, used for storing audio, video, data

Memory Hierarchy Registers Cache Level I, Level IICache Main (RAM)RAM Auxiliary (Hard Disk, SSD (based on flash)) Access time and transfer rates depends on each type of memory. Why not use fastest? (RAM: ns; SSD: µs; HD: ms) Cost/speed tradeoff. Caching techniques to gain advantage of fastest memory

Flow of Information Bus A bus is a subsystem that transfers data between computer components inside a computer or between computers. Figure 5.2 Data flow through a von Neumann architecture

Bus

The Fetch-Execute Cycle Figure 5.3 The Fetch-Execute Cycle

Alternative Architectures

Pipelining Arranges processors in sequence, where each processor contributes one part to an overall computation. - example utility…

Example: non-pipelined Compute (4x+8)/2 for list of data x. Compute (4x+8)/2 for list of data x. Assume we have three processors. Assume we have three processors. Sequential execution model Sequential execution model Data x Processor 1 computes ((4)(3)+8)/2, then ((4)(7)+8)/2,... Processor 2 Processor 3

Pipelined: compute (4x+8)/2 Data x: 3, 7, 2, 5, 1, 6, 8, 4, 10 Time Processor 1 (mult by 4) Processor 2 (add 8) Processor 3 (divide by 2) 1 4 x 3idle 24 x idle 34 x /2 44 x /2 54 x /2 64 x /2 74 x /2 84 x /2 94 x /2 10idle40+824/2 11idle 48/2

Distributed memory One approach to parallelism is to have multiple processors run on different (multiple) data sets - might have same program running on separate data - might have different programs running on separate data - makes sense when data is cleanly separable for the purpose of the problem

Example: compute sum of long list of numbers First numbers next numbers numbers numbers last numbers divides up the numbers distributes to difference processors adds them all together at end This model is relevant not only for parallel processing within a single computer, but in distributed computing across many different machines (e.g., in a data farm)

Shared Memory Communicate through shared memory allows programs to leave messages for each other, e.g., to farm out part of a computation to other processors need to be careful that processors don’t overwrite what each is doing avoids redundant copies of data – - except for caching and cache coherence problems

Computer Components Consider the following outdated ad

Example Specs retina/ retina/

Computer Components What does all this jargon mean? Intel Pentium 4 Processor at 3.20 GHz Intel Pentium 4 Processor at 3.20 GHz 512 MB Dual Channel shared SDRAM at 400 MHz 512 MB Dual Channel shared SDRAM at 400 MHz 80Gb Ultra ATA/100 Hard Drive 80Gb Ultra ATA/100 Hard Drive 17" flat-panel Display 17" flat-panel Display 8X DVD + R/+RW Drive with CD-RW 8X DVD + R/+RW Drive with CD-RW Altec Lansing Surround Sound Speakers Altec Lansing Surround Sound Speakers Integrated 5.1 Audio with Dolby Digital Integrated 5.1 Audio with Dolby Digital WordPerfect and America Online WordPerfect and America Online

Sizes in Perspective

Intel Processor speed 3.20 GHz SDRAM size 512 MB speed 400 MHz Ultra ATA-100 Transfer rate 100MB per second Flat screen dot pitch.28 To which do these apply? Bigger is better Faster is better Smaller is better

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

Input

Output devices Output devices

Touch Screens - both I and O A touch screen (Randy Allbritton/ Photodisc/ Getty Images © 2003 Monitor responds to the user touching the screen with a stylus or finger –Resistive –Capacitive –Infrared –Surface acoustic wave (SAW)

Touch Screens Resistive touch screen A screen made up of two layers of electrically conductive material –One layer has vertical lines, the other has horizontal lines –When the top layer is pressed, it comes in contact with the second layer which allows electrical current to flow –The specific vertical and horizontal lines that make contact dictate the location on the screen that was touched

Touch Screens Capacitive touch screen A screen made up of a laminate applied over a glass screen –Laminate conducts electricity in all directions; a very small current is applied equally on the four corners –When the screen is touched, current flows to the finger or stylus –The location of the touch on the screen is determined by comparing how strong the flow of electricity is from each corner

Touch Screens Infrared touch screen A screen with crisscrossing horizontal and vertical beams of infrared light –Sensors on opposite sides of the screen detect the beams –When the user breaks the beams by touching the screen, the location of the break can be determined

Touch Screens Surface acoustic wave (SAW) A screen with crisscrossing high frequency sound waves across the horizontal and vertical axes –When a finger touches the surface, corresponding sensors detect the interruption and determine location of the touch

I/O Trend towards integration of I&O Trend towards integration of I&O –touch screen (input = stylus or fingers, output = monitor display) –haptic devices (input = movement and positioning; output = tactile feedback) Trend towards more user-engaged I&O Trend towards more user-engaged I&O – DDR, Guitar Hero, Rock Band, iPhone, Wii, VR helmets. Entertainment industry and HCI fields driving innovation. Google glass Google glassGoogle glass Man/machine interface Man/machine interface Man/machine interface Man/machine interface