An Operating Systems Vade Mecum

Device hardware 1551.5 Summary of device characteristicsWe have concentrated on magnetic media (disk and tape) and transmission lines becausethey are often more complex than paper and card equipment. However, it is often usefulto know the characteristics of various devices in order to compare prices, capacities, andspeeds. The following table displays the current situation for typical devices.Bytes Bytes Bytes Cost Cost Medium Device per per per per per record second medium medium ($) device ($)Reader 120 1−2K 120 < .01 8−40KCardsPunch 120 1K 120 < .01 20−30KDot matrix — 30 5K .03 200 Daisy — 100 5K .03 300 Paper Train printer 132 1−7K 9K .03 12−75K Laser printer — 1−25K 5−10K .03 2−300K 9-track — 120−390K 50M 10 12−50KTapeStreaming — 100K 80M 5 1−3KFloppy 256 100K 100−500K 1 500DiskHard 512 1−3M 10−1000M 1−10K 1−50KDrum Fixed head 512 1M 2M — 20KGlass tty — 1K 2K — 500DisplayBit-mapped — 1M 100K — 1−5KNotes:(1) One can typically stack up to 3000 cards in the bin on large card readers andpunches.(2) Laser printers are limited in speed both by their connection to the computer(often a 9600-baud line) and by the speed at which they can emit paper (rangingfrom 10 to 200 pages a minute). They have resolutions ranging from 300 to 600dots per inch, so they can effectively print about 2M bytes per page.(3) The figures for magnetic tape are for 2400-foot reels at 1600 frames per inch.One can also get 600- or 1200-foot reels, and they can be written at densities of800, 1600, or 6250 frames per inch. The latency for starting the tape or stoppingit is about 5 milliseconds. Tape drives usually need controllers, which cost about$20K.(4) The seek latency for a small floppy is about 0.2 seconds.(5) The seek latency for a drum about 4 milliseconds. Drums are no longer common.(6) Displays can usually run at a number of speeds, ranging from 10 to 1920 charactersper second. They hold about 24 lines of 80 characters.