Double Sided Double Density Mystery Cache

The 8" floppy disk was originally developed by IBM in the early 1970's to load software for their mainframes. The original format could hold 80KB of data, and later up to 256KB, which was just enough to store the equivalent of 1 box of punched cards and was a revolutionary technology providing random access to the data.  In the early days of personal computers, these drives often cost more than the computers themselves, so most people opted for cassettes instead. The disk was divided into 77 tracks of 26 sectors (a total of 2002 sectors), each holding 128 bytes. Eventually improved formats yielded 500KB by using both sides, and 1.2MB by using 8 1024 byte sectors per track.

In the late 70's, Wang Laboratories declared the 8 inch disk too big for the word processing units they were developing at the time, and came up with the 5.25" size over a lunch, and pointed to a napkin saying 'about that size.' These disks and drives were cheaper than the 8" disk format, and they quickly took over the market. These were popular with most personal computers in the late 70's through 80's such as the Apple II, Atari 8-Bit, Commodore's, IBM PC's and more. The most popular format was a double sided 40 tracks, 9 sectors per track, 512 bytes per sector, yielding 360KB. Atari & Commodore used twice as many 256 Byte sectors, yielding the same storage space, but incompatible between platforms. Apple used custom hardware and software to manage and access the disks, they had a formatted capacity of 113K, 23K more than the capacity offered by Shugart. Most of the electronics of the original Shugart drive were eliminated during design by Steve Wozniak with his electronic engineering skills on the PCB design, and replacing many functions in software, making it the cheapest disk drive ever offered at the time, even at a $595 introductory price.

In 1981, Sony introduced the first 3 1/2" floppy drives and diskettes. These floppies were encased in hard plastic, however, the name stayed the same. They stored 400kb of data (Single Sided Double Density), and later 720K (double-sided, double-density) and 1.44MB (high-density). These drives were first used in Apple's Lisa computer, and soon followed by IBM, Atari, Commodore, and others. The size was decided upon, as it was the smallest size without fitting into peoples' shirt pockets.

The most popular format of 3.5" disks in IBM PC's and Atari ST's was the Double Sided-Double Density format: 80 Tracks (Cylinders) 9 sectors per track, per side, and each sector having 512 bytes, totalling 1440 sectors, or 720KB. Later in 1986 "High Density" disks arrived that used an improved encoding method to have 18 sectors per track, per side yielding 2880 sectors, or 1.44MB total.

Computer enthusiasts would always try to push the limits of technology, and I remember using specialized formatting utilities to format disks with 10 or even 11 sectors per track, and up to 83 tracks, allowing over 900KB of data to be stored. 10 sectors was pretty safe, but 11 often resulted in your data being unreadable after a short period of time... And most drives could read 81 0r 82 tracks, but I remember the sound of some drives at track 82 or 83 making a very definite 'clunk' when it hit the 'end of the road' inside the disk drive, causing a read error for that track, and potentially throwing your drive permanently out of alignment. :)

Your challenge to calculate the coordinates of this cache, is to determine the LBA (sector number) of a physical disk location by Track (Cylinder), Sector, and Side of a 720KB IBM formatted 3.5" floppy disk.

Please replace the cache exactly as you found it, and bring your writing utensil!