![]() ![]() And the 5” disks had exactly half the data rate, 125,000 bits per second, vs. Those 5” disks would spin at 300 RPM (5 revolutions per second), a little slower than the 360 RPM (6 revolutions per second) of 8” disks. As far as I know this format was unique to North Star, and the rest of the industry evolved to use 40 tracks on the 5” disk with soft sectors. The disks were “hard-sectored”, with 11 holes punched into them (10 for the sectors and an extra for the index). The North Star system used 5” disks with 35 tracks of 10 sectors of 256 bytes, for a total capacity of 89,600 bytes. The sector start could only be determined by reading from the disk. This means the disk was “soft-sectored”: there were no physical indications of sector boundaries. A single small hole was punched into the disk near the hub as the “index”, or starting point of each revolution. The 8” disk came first, introduced by IBM with 77 tracks of 26 sectors, each storing 128 bytes of data, for a total capacity of 256,256 bytes. We used North Star, Cromemco, and Tarbell floppy disk controllers, and later designed a floppy disk controller of our own (the “Disk Master”).įloppy disks came in two sizes, which we called 5” and 8” (but the 5” was really 5.25”). Seattle Computer Products adapted DOS to an array of floppy disk systems. ![]()
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