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The 5-1/4" floppy disk drive was introduced in 1976 as a low cost alternative to the 8" IBM standard flexible disk drive. Originally aimed at the blossoming small business and personal computer industry, these small, low-cost drives offered a maximum unformatted data capacity of only 110 kbytes. Although the 5-1/4" floppy is now 2 years old, most drives being shipped by the handfull of 5-1/4" floppy manufacturers is still capable of only 110 kbytes of storage. Because of the popularity of the 5-1/4" floppy and increased demand for storage by the suppliers of microcomputer systems, most of these manufacturers are now trying to increase the capacity of their drives by in creasing bit density (using MFM or M2FM recording techniques) and/or using double sided heads. One manufacturer, however, Micropolis Corporation, Canoga Park, California, has been offering a drive since the spring of 1977 which provide 4.4 times the normal density on a single side of a standard 5-1/4" diskette. First available only in disk memory subsystems, Micropolis' 480 kbyte unformatted capacity drive is now supplied, on an OEM basis, to many microcomputer system manufacturers. Originally viewed as a novelty, the drive is now widely accepted as a highly reliable alternative to other low capacity 5-1/4" drives. Micropolis expects to ship nearly 20,000 drives over the next year. The double-sided Micropolis drive now being supplied in evaluation quantities is capable of I megabyte of storage per drive! How has Micropolis been able to offer so much more capacity? The drive mechanism incorporated two technologies already well-proven in the peripheral industry yet not then introduced to 5-1/4" floppy design: Increased Bit Density ------ MFM Data Recording Increased Track Density ---- 100 Tracks per inch (77 tracks total) MFM (Modified Frequency Modulation) increases the nominal capacity of 110 kbytes to 220 kbytes. The increase from 35 tracks to 77 tracks yields 77/35 X 220 = 480 kbytes.

A bipolar technology floppy disk controller using LS, I2L and analog circuitry will be discussed, citing system level advantages such as an on chip PLL.

This report will cover the use of one CMOS and two bipolar ICs to provide analog and digital signal processing for 25Mb/s Winchester disk drives. A single chip 25Mb/s data separator-encoder realizes both modified frequency modulation and