Re: A Silly Database Question

howfie wrote:
"Walter Mitty" <wamitty@xxxxxxxxxxx> wrote in
news:wDpZl.1097$P5.777@xxxxxxxxxxxxxxxxxxxx:

"Tony Toews [MVP]" <ttoews@xxxxxxxxxxxxxxx> wrote in message news:t86b35lf6hqj2niterb2hirsni7cm300vr@xxxxxxxxxx
howfie <yadayada@xxxxxxxxxx> wrote:

I couldn't find this information on Google, but why is the
visual representation of a database (in presentations and
graphical descriptions) always a can or a cylinder? Is it
because hard drives contain cylinders or is it because that
is what hard drives used to look like before the rectangular
ones appeared?
Correct. See
http://en.wikipedia.org/wiki/Early_IBM_disk_storage#IBM_3330 for a
picture of such. And that is basically what you would see inside a modern hard
drive. Mind you that one is 200 Mb. I've seen others in 1979 which
were mounted in
a machine slightly narrower than a washing machien and were 10 Mb.
Also see the wikipedia article on drum memory.
Cool, thanks for all the info guys. I just wanted to be 100%
sure before I said anything to my database students or add
it to my powerpoints :-).

Josh

http://en.wikipedia.org/wiki/Magnetic_drum

The picture of the drum in the article really looks like a can. Drums
fell out of favor when compared to discs, because moveable heads made
for much cheaper construction.
In addition, stacking disk on top of each other in cylinder fashion
allowed you to pack more media onto the same square footage of floor
space. The great timesharing computers of the 1964-1982 time frame
all used discs of various sizes and capacities, as did the giant
database mainframes of the era. The early computers in the 1950s
tended to use drums for main memory, before core memory gained
widespread use. See the article on the IBM 650. http://en.wikipedia.org/wiki/IBM_650



I must say I thought it was one of the greatest questions I've ever seen here. And half-thought it was a send-up until Walter replied! If this is for real, maybe you should point out to the kids that the cylinders were and are 'virtual', get them used to what that term can mean.


Once, I was given a 2321 (if I recall the model), sometimes called a spaghetti picker. Real Buck Rogers concept, half disk and half tape (with an astounding 500 msec access/latency time) but with serious engineering, like a three-horsepower motor labelled "lubricate every twenty years", no guff. Serious Nasa-style hydraulics, twenty gallon reservoir and compressed nitrogen. I couldn't afford to hook it up. I knew a really smart programmer but much younger who asked me what a mainframe disk looked like. I told him the box that held seven or eight of them was taller and longer than him so the 'Customer Engineer' (who was a regular presence at all big IBM installations right up to about twenty years ago) could get his head inside. Unfortunately it seems one CE was decapitated which resulted in an EC, so-called "engineering change".


When I thought again about his question afterwards I remembered how much closer programming was to manual labour I was envious of that kid because he had saved himself a lot of wasted years and I wished I had been born later. On some smaller machines even in the 1960's, people used tape drives for working storage to sort. These days, for myself, I just use solid state stuff.


In those days a macho term among assembler programmers was 'bare-metal-programming', which the typical disks encouraged with the 'Count-Key-Data' instructions that were wired into their controllers. Thankfully, modern disks have abstracted out that physical nonsense. The same people considered it important to flip three thousand cards without spilling them and looked down their noses at any object deck that was thinner than three or four inches.


Then there's memory capacity. Did you know that even into the 1990's a typical PARS/ACP flight reservation system for a medium-sized airline (say 100-300 planes) occupied only about 300MB disk space? I have to wonder how things would be now if today's main memory were available then, a lot of decisions would have been different. Of course we know what really happened to that memory - as a friend who was an IBM salesman in the 1960's was told when some 512KB memory cpu's came out: "your customers can't use it, we need most of it for OS/360'. In those days the famous IBM motto was "THINK" and they used to give out desk plaques to remind you to do that. I saw one that had been graffitee'd to say "THINK OR THWIM".
..
.

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