bcase@amdcad.UUCP (Brian case) (08/02/85)
[line eater...] Following is an excerpt from an old Apple user's group newsletter based in Scottsdale AZ (I have no idea if the group still exists or what). There are those (in particular, the guy who gave me the copy of the newsletter) who believe that the author of the article was serious in his concern for computer inertia. I have my doubts, but reading it is fun. Anyway, if the following were true, then a system based on a 16MHz 68020 would probably slide off of the table when halted. Please, no flames, I am just trying to add some levity.... ------------------------------------------------------------------------- POTENTIAL PROBLEM by Jerry W. Fewel I need to take this opportunity to write a serious article on a subject that is of grave concern to us all. The computer stores that sell computers do not normally give their customers this information, but it is something in which all Apple owners should be aware. This is a problem that is indicative of all processors. This is the computer problem of program inertia. Everyone should be aware that inertia is a physical law of science that cannot be prevented. Inertia is energy stored within any moving object which fights any change of momentum or directional change. The same scientific prinicipal also applys to a running computer. If I give you an example of the speed of a computer, you will under- stand what I'm trying to say. The sun is approximately 93,000,000 miles from the Earth and light takes a little over 8 minutes to make this trip. In just one second, light travels over 186,000 miles. Now let us look at our Apples. The time that the Apple takes to read memory only gives light a chance to travel a little over 600 feet. The time required to read any register only gives light a chance to travel about 14 feet. Every instruction cycle consists of a minumum of one memory read and may have two and can have as many as three memory reads and one memory write. Each instruction that is performed is immediately followed by entering the next instruction. The time for the average instruction may only give light a chance to travel 1200 feet. At this speed, over 800,000 instructions are being performed every second. It only takes about 3 seconds to build up the maximum amount of inertia. This is called program inertia and you can safely believe that this is a tremendous amount of stored energy. You may not be aware of this, but to remove stored energy from an object takes the same amount of opposite energy. For example, if you were pushing me with a force of 50 pounds, then in order to remain where I am, I must push back with an equal force of 50 pounds. If the opposite force is not exactly oposite (an angle other than 180 degrees) then it would require more combined force from at least two vectorial directions. I do not intend to take this space to explain vector analysis. This is the main reason that manufactures have removed the control panels from the home processors. It was found that every time the halt switch was pressed the small processors would overrun from between 3 to 5 instructions. This is like running as fast as you can, and trying to stop in one step (without running into a wall). Halting any computer is a tremendous strain on the memory chips (because of the extreme timing changes). and the power supply (because ofthe excess surge current). To help remedy this problem, the control panels were removed so that the computer would always be in a run mode of operation. This way, the only large strain on the system is during power down. The Apple power supply was designed with a large filter capacitor across the 5 volt line in parellel with the SCR that handles the crowbaring of the excess current. This insures that the power comes down gradually and smoothly. This helps to decrease the strain on the power supply as this energy is expended into a halt or non-run mode. This leaves only the strain on the memory and we all have to contend with this problem manaully. It is better not to power down the Apple while running a program because programs reside in memory. It will be much better to do a "CALL-151" first. This will put you in the monitor which resides in ROM. The ROMs in the Apple are especially designed to withstand the strain caused by the program inertia more than the memories. If powered down while you are in the monitor, you have a better chance of the system comming back up next time you turn the unit on. For more information on computer inertia, you might want to contact [name deleted]. He is connected with a local repair representative in this area and is fully aware of the hardware problem that can be caused.
bcase@uiucdcs.Uiuc.ARPA (08/02/85)
[line eater...] >Following is an excerpt from an old Apple user's group newsletter >based in Scottsdale AZ (I have no idea if the group still exists >or what). There are those (in particular, the guy who gave me the I forgot to mention that the typo's, gramatical errors, and other weirdnesses in the article are from the original; I typed it just as it was given to me. bcase
dsi@unccvax.UUCP (Dataspan Inc) (08/03/85)
I hear that people put this 'computer' (electron) inertia
to good use. Instead of corrupting your computer programs, there are (not
strictly) devices such as 'klystrons' etc. Hmmmmmmmmmm?
Not to flame, but this kind of garbageola is what is screwing our whole
country. Will someone please calculate 1) the number of femtofarads that
an individual memory cell is composed of and 2) the mass of the charge and
3) calculate the inertia available to rip the little chip right out of the
board?
If you've got a CPU running at 800,000 instructions per second, you
should seriously contact 'That's Incredible' if you can stop the thing
within 3 or 4 instructions of the desired instruction!!! What split
second timing!!! (Of course, using a mechanical switch connected to
the ~HLT pin or whatever).
The posting itself is foolish. The problem, though, is extremely
serious.
David Anthony
DataSpan, Incbill@persci.UUCP (08/05/85)
>[line eater...] >Following is an excerpt from an old Apple user's group newsletter >[...] > POTENTIAL PROBLEM > by Jerry W. Fewel > > I need to take this opportunity to write a serious article on a >subject that is of grave concern to us all. The computer stores that >sell computers do not normally give their customers this information, >but it is something in which all Apple owners should be aware. This is >a problem that is indicative of all processors. This is the computer >problem of program inertia. >[...] At this speed, over 800,000 instructions are being performed >every second. It only takes about 3 seconds to build up the maximum >amount of inertia. This is called program inertia and you can safely >believe that this is a tremendous amount of stored energy. >[...] This is the main reason that manufactures have removed the >control panels from the home processors. It was found that every time >the halt switch was pressed the small processors would overrun from >between 3 to 5 instructions. This is like running as fast as you can, >and trying to stop in one step (without running into a wall). > Halting any computer is a tremendous strain on the memory chips >(because of the extreme timing changes). and the power supply (because >ofthe excess surge current). >[...] This leaves only the strain on the memory and we all have to >contend with this problem manaully. It is better not to power down the >Apple while running a program because programs reside in memory. It >will be much better to do a "CALL-151" first. This will put you in the >monitor which resides in ROM. The ROMs in the Apple are especially >designed to withstand the strain caused by the program inertia more >than the memories. >[...] For more information on computer inertia, you might want to >contact [name deleted]. He is connected with a local repair >representative in this area and is fully aware of the hardware problem >that can be caused. Sort of reminds me of something I saw in Datamation, I think, about a decade or so back, probably in the April issue: ...(program)... 100 STOP ;Stop program STOP STOP GOTO 100 ;In case still skidding.. Try it out! -- William Swan {ihnp4,decvax,allegra,...}!uw-beaver!tikal!persci!bill