This one is from the school days. We had a compulsory basic computer classes in class 8. The day the teacher started to describe how a computer hard disk work, under input/output chapter. He told there were some platters, ie. disks inside the hard disk box, and they rotate in very high-speed, and as the head positions itself in the proper location over the platter and flies on it the data is read. Everything was pretty fine till now until the next thing was told. He said, “when one platter is full with data it moves down the stack of the platter to the bottom, and the next disk is used”. “Woah!, OOohh!, Ure Sala!” these were some of the reactions from the students. He continued, “and that’s why hard disk drives are slow, it needs to switch platters when some data is needed is not in the current platter”. Some body protested using his common sense, “where is the space for the platter to move down the stack?”. Answer was “it might seem there is not enough space but it actually is designed like that.”
Next day another teacher came to class, everybody told him about this, his reactions were: “Did he say so? Really? ….. He has gone mad. Ok let it go ..” , and he described the real mechanism of the hard disk.