CS 162 Lecture 3-14-2005 IO DEVICE CHARACTERISTICS Raster Printer -------------- * Page consists of an array of pixels. Typical density is about 300-1200 pixels per linear inch (about 8 million pixels per page). * Each dot can be made black or white individually, so you can create new fonts and draw pictures instead of just the default text of a line printer. * Print rate = 5-30 ppm (pages per minute), fastest 55 ppm * Most raster printers use lasers and xerographic tech- niques, or ink jet. * Xerox (xerographic technique) You have a selenium-coated drum and a thick black sludge called toner, made of carbon particles. Light is reflected on the document to be copied, which is reflected onto the drum. This charges the particles on the drum at the places where there is an image on the paper. Toner is applied to the drum and sticks to the charged areas. Then the toner is rolled over the paper. Finally, the toner is melted onto the paper. * Laser printer Laser writes directly onto the drum, allowing you to create any image. * In a typical color laser printer, the paper makes four passes around the imaging drum to pick up each successive layer of toner (one pass each for cyan, magenta, yellow and black.) Print speed is thus 1/4 of normal. Expensive printers use 4 lasers, one for each color. * Newer color "laser" printers use LED arrays in- stead of lasers for the print heads. The engine can contain four print elements (one per color) arranged in a line, so that the paper can move along a straight path to pick up all four colors in a single pass. * Ink-jet Squirts out small droplets of ink. Ink drops can be generated either by heat (by boiling out a small amount) or by pressure on the cartridge. * The hardest problem in printer technology is paper mechanics. Very difficult to manipulate the paper properly and reliably, as you can see by the high failure rate of this part of printers. Q - Do you see HP building printers for the next 10-20 years? A - I don't see paper copies and printing going out of style. Paper is very useful and economic. All-electronic book technology has not been very successful. Note: Work has been done on digital paper. It looks and feels like paper but you can reuse it. Uses OLED technology (see the OLED section later) Displays ======== CRT - Cathode Ray Tube ---------------------- * A phosphor-coated screen glows when an electron beam strikes it. * High voltage generates electron beam. Electro- magnetic field deflects the beam onto specific pixels. * Color is obtained by having different pixels for each color. Beam only writes to appropriate sub- pixels. * Shadow mask technology uses three beams, one for each color. * Technically possible to use CRT for storage. High-persistence phosphor leaves data on the display for a long enough time to refresh data. LCD (Liquid Crystal Display) ---------------------------- * Each pixel is a liquid crystal which can be ori- ented by an applied electric field. * Each pixel is turned on/off by either: Column and row select ("passive matrix") or Individual transistor on each pixel ("active matrix" or "thin film transistor"). Active matrix is better and more common. * Light is provided by a backlight. Light from the backlight passes selectively depending on whether the pixel is on or off. Uses 1.2 to 2.4 watts (total power for LCD is around 2-5 watts). * Colors are provided by having sub-pixels and color filters over each. * Manufacturing is very difficult, like silicon chips, resulting in a yield problem. Thus they are very expensive. * Response time: 150ms for passive, 40ms for ac- tive. Response time determines how quickly pixels respond to changes in the display. Low response times relative to CRT mean that LCDs have a harder time with moving images. * LCDs often come with a certain number of dead pixels that are tolerated by the manufacturer, which is unfortunate. Newer Technologies ------------------ * OLED (Organic Light Emitting Diodes) Emit light when a current is applied. Short lifetime for certain colors. Still in early stages of adoption. * Plasma Plasma radiates and causes phosphor to emit light. Short lifetime. Cheaper than LCD, but not as good. Commonly used for large television displays. * Field Emitter Display Electron gun behind each pixel. * Electroluminescent Display Some semiconductors emit light when a current is passed through them. Think LED. * Electromechanical Manipulates light with mirrors. Can be used in a projectors. Ex, TI Mirror Chip. * Retinal Scanning Lasers Writes the image directly on your retina. Tape ==== Reel to Reel Tape ----------------- * 9 tracks (9-bit) * 1/2" wide by 2400' long Also comes in 600' and 1200' reels. (Old tapes were 7 track. No longer used) * From 800 to 6250 bytes per inch (bpi). (Old tapes were also 200bpi and 556 bpi) * Bit density was so low you could read the bits with a magnifying glass. * Max capacity of 6250 tapes is about 180 Mbytes. Diagram of tape. start __ __ end /..\ /..\ |\__/ \__/| | | | __ | <- Magnetic tape \ /..\ / \___/\__/\___/ * Same technology as audio cassette. Tape base is coated with thin magnetic coating. The write head magnetizes small bits on tape surface. * Variable length records on some machines (about 1-32000 bytes). * Inter-record gap is about .6 inches. With many small records, the inter-record gap may lead to a lot of wasted space. * Tape moves at 20-200 inches per second. Max data rate is about 1.25 Mbytes/sec. High speed drives use air columns to avoid tape reel inertia. * Can read or write, but cannot write in middle, o/w you might overwrite another block. Can skip records. Q - What is the life cycle of tape? A - Tape won't keep magnetization forever. Magnets demagnetize, the tape deterioriates physically, and bits that are close together can affect each other, leading to "write-through." * Tape is normally read only one direction. On some machines (e.g. IBM 370), can read tapes backwards. This is not easy to do, since it requires system calls in assembler. * Tapes are DMA devices, not one interrupt per charac- ter. * High performance tape drives are expensive - up to $30000, plus the cost of a controller. * IBM tapes have some standard formats. Can be labeled (every file has a standard header). This minimizes the probability of overwriting the wrong tape if the operator makes a mistake when retrieving it. * Disks and tapes read and write blocks of information rather than single bytes * Storage Efficiency: For tapes written at 1600 bpi, 80-byte records use .05 inches, gaps use .6 inches => Only about 1/12 of the tape is used productively However, 8000-byte records use 5 inches so gaps are only about 11% of the total tape. * Example: HP 1/2" tape (rack mount) (1993) Density - 6250bpi Capacity - 140MB MTBF - 22,400 Hours (Mean Time Before Failure) Speed - 125 inch/sec Transfer Rate - 781 KB/sec Power Usage - 170-120 Watts Rewind Time - 90 sec for 2400' * Newer tapes (IBM 3480 type) are cartridges (about 6" x 6"). Hold about same capacity as 2400' tape. 18 tracks. 220MBytes. Cost (end user, 1990, IBM - $95,000) * Example: Cranel (1992) Tracks - 18 Length - 540' Width - 0.5" Cartridge Size - 1" x 4.3" x 5" MTBF - 15000 Hours, Speed - 1 meter/sec Transfer Rate - 3MB/sec Capacity - 200 MB 3480 compatible * Used in automated tape libraries. DECtape ------- * "randomly" readable and writeable. Used on DEC minicomputers as cheap addressable storage. Now obsolete. Used in the 1960-70s. DAT tape -------- * 4mm tape in a DAT cartridge (smaller than audio casette). * Capacity about 1 - 2Gigabytes. * Uses 3 level error correction. Error rate is 1 in 10^15. * Uses embedded subcodes to find files and tracks. Tape is blocked in 512KB blocks. Can fast forward to appropriate block. Data is also organized into groups of 126,632 bytes. Each group contains 22 logical data frames of fixed capacity. * There is a mode which permits random read/write. Must preformat the tape into frames. This is called "update in place." * Head/tape speed of 123 in/sec. * Track angle: 6 degrees. * Uses 2 read heads and 2 write heads. Write tracks in a herringbone pattern, which can overlap without interference. * Example: Hewlett-Packard (1993) Capacity - 2 GB Transfer Rate - 183 KB/sec Avg Seek Time - 30 sec Power Usage - 3.9 Watts MTBF - 50,000hrs Note: One version is available with data compression, capacity increased by a factor of 2-4x. * Example: Cranel (1992) Capacity - 1.3 GB Length - 60 Meters Transfer Rate - 183 KB/sec max sustained Burst Transfer - 1.5 MB/sec MTBF - 40,000 Hours Error Rate - 1 in 10^15 Search at 200 times faster than normal Exabyte tape ------------ * 8mm tape in a cartridge. Holds 2.5-5.0 GB. * Helical scan device. This method allows the tape to be moved slowly, thus saving costs but still achieving high data density due to the fast spinning head. Offers slower tape speeds than linear scan and the potential for higher capacities on a cartridge. * 1995 model Capacity - 5 GB Transfer Rate - 500 KB/sec Tracks - 9 Density - 75 MB/in^2 Speed - 0.5 in/sec, (150 in/sec relative to head) 246KB sustained data rate. * Higher speeds could be obtained by faster drum rotation and higher linear bit densities. 3 MB/sec possible. * Example: Cranel: Transfer Rate - 1.5 MB/sec peak, 246 KB/sec sustained Density - 34200 bits/in, 819 tracks/in, 35 million bits/in^2 Speed - 0.429 in/second tape speed, rotor at 1800 rpm -> effective tape speed 150in/sec Rewind Time - 75 times normal Search Speed - 10 times normal MTBF - 20,000 Hours Error Rate - 1 in 10^13. DLT Tape (Digital Linear Tape (Quantum 2004)) --------------------------------------------- * Records data in aserpentine pattern - along length of tape, then reverse and back. * Dimensions - 4.1"x4.1"x1" * Length - ~2000' * Width - 0.5" * Durability - 1M passes. * MTBF - 250,000 Hours * Capacity - up to 300GB/tape (before compression) Compression increases by 2X. * Transfer Rate - Up to 36 MB/sec * Burst Transfer - Up to 200 MB/sec. * Track Density - ~1490 Tracks/in (640 tracks serial serpentine) * Error rate - uncorrected 1 in 10^17 undetected 1 in 20^27 * Record Density - 233 Kbits/in * Power - 32 Watts * Access Time - Avg 79 sec * Tape life is >30 years, quoted "less than 10% loss in demagnetization at 20C and 40% non-condensing humidity." Professor doesn't think much of that claim. * Low End Version Capacity - 40GB (uncompressed) Tranfer Rate - 3 MB/sec Tracks - 168 Record Density - 123 KBits/in Track Density - 336 tracks/inch MTBF - 200,000 Hours Power - 15 Watts Other Tapes ----------- * Variety of other tape formats available. * Two general formats: * Linear tracks - Tracks are along the length of the tape. _________________ | | | | | | | | | | ----------------- _________________ / / / / / / / / / ----------------- * Helical scan - Tracks are diagonal along tape. * Variety of sizes of tape, lengths of tape. * Variety of tape reel sizes. Some are two-reel cartridges. Tape Issues ----------- * Tapes deteriorate over time. * Variety of formats - mutually incompatible * Tapes are slow. Usually 1-3 MB/sec, except for very high end. * Formats become obsolete. May not be able to read in future if you can't find a drive to read it. * High end tape drives are expensive. * However, tapes are THE cheapest way to save massive amounts of data. Advances in hard disk technology may be changing that though. Hard Disk ========= * Read/Write Arm Controls the head. Seeks to the a platter and performs reads and writes. One arm for eac platter. All arms move at the same time. * Platter Magnetic-coated disc, holds your data. Can be 2 surfaces on each platter. In that case, there is a head for each surface. * Track Platter is made of concentric circles called tracks. * Cylinder Term for all the platters underneath a single track. Basically, all tracks that can be read now without moving the arm. * Sector The disk platter is divided into wedges by radial lines. A sector is the portion of one of these wedges within a particular track. It is the fixed size of a read/write block. I deeply apologize for this terrible ascii art. ______________ / /\ / / \ / / \ | / | | /_______| | | <-- Platter | | \ / \ / \______________/ ------ <--- Read/Write Arm | \/ <--- Head | --------- <--- Platter <-\ ------ | | \/ | | --------- |-- Cylinder ------ | | \/ | | --------- <-/ * Technology similar to tape. Heads float over disk sur- face, at a distance about 1 micron (millionth of a meter), which is considerably less than width of human hair. If disk becomes contaminated with something even as small as a dust particle, the head can crash. * Data can be written in variable size or fixed size blocks (sectors). IBM style high end disks permit variable size blocks (called "count key data (CKD) disks"). Most other machines usually use fixed sectors of 512 bytes. Q - How exactly do you write on a platter? A - The head induces a magnetic field in the magic material, which flips the N-S orientation of the magnetic for each bit. * Material written looks like a tape block: Inter-Block Gap Key Field Control Info Physical Block Address Record Number Error Correction Key Length Byte Count Data * Overhead for variable blocks is about 50-100 bytes, plus Inter-Record Gap. Smaller overhead for fixed blocks. * Most disks used to be removable. Now no hard disks are removable except ZIP (100, 200, 750MB) and JAZZ (1-2GB) disks by IOMEGA, Syquest, etc. The last "major" removable regular disk was IBM 3330. Removable disks are not reliable, since the place where the head will go on disk depends on the reader. This is not a problem if the head is always packaged with the disk, like in Microdrive. * Disks can be mounted in external enclosures. However, these are usually more expensive for less speed and capacity. * CompactFlash Type 2 is a tiny hard disk, the MicroDrive. It is 1" on a side and can hold 5 GB of data. Floppy Disk =========== * Capacity - 1.44MB * Speed - 60KB/sec * Obsolete, useless! Nowadays, flash memory can simulate a disk's interface. Plug it in and it looks like another drive. Convenient. Q - Isn't a flash drive limited by USB speed? A - Yes, but USB 2.0 is much faster than the drive's speed, so it doesn't actually limit it.