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Re: Core memory Re: Old farts and new Linux



On Tuesday 04 May 2004 20:16, Jeff Vian wrote:
>jludwig wrote:
>>Keith corrected me on this which is ok since I had an Old (brain)
>> fart! It's nice to see someone who knows or remembers, and I find
>> this reminder very interesting and educational.
>>
>>On Mon, 2004-05-03 at 19:23, Keith Lofstrom wrote:
>>>You wrote:
>>>>For those who don't know what core memory is, it's miniature
>>>> ferrite beads strung together with three wires through them to
>>>> read/write [magnetize and demagnetize], and reset if I remember
>>>> correctly. I have seen 16 MB of core memory, it was the size of
>>>> a full size tower case.
>>>
>>>Some corrections of fact, which I will share with you privately.
>>>You can research and post;  it is always better to correct
>>> yourself than have someone else do it publically.
>>>
>>>The three wires in a core memory are X select, Y select, and
>>> sense. The cores work by pushing an X current and a Y current
>>> through an intersection; two currents pushed the hysteretic
>>> toroidal magnetic core past a threshold, either causing it to
>>> flip magnetic polarity (generating a little voltage blip on the
>>> sense line) or not, depending on previous magnetization.  After
>>> flipping a core during a read, you had to schedule a reverse set
>>> of currents on the same X and Y wires to put the core back.  The
>>> size of the arrays were limited by the number of cores you could
>>> put on a sense wire before accumulated noise made reading
>>> unreliable.
>>>
>>>A friend in high school wanted to build a core memory, and wrote a
>>> letter to Honeywell.  They sent him a one pound jar of 15mil
>>> cores.  All out of spec, as near as we could measure.
>>>
>>>What you probably saw was a 16*K* byte memory, the boards from the
>>> late 60s were typically around 16K bits, 8 boards to a byte, and
>>> about as big on a side as a tower case with the small scale
>>> integration driver chips around the sides of the core fabric.  A
>>> 16MB machine would have been gargantuan, indeed;  I would guess
>>> 100 or more 19inch racks, 8 feet tall, and probably costing on
>>> the order of $50M in current dollars.
>>>
>>>Keith
>
>yeah, things were big and expensive.
>In 1990 the military base where I was stationed finally upgraded the
> IBM mainframe they used to 64 mb memory.  They had been running on
> 16 mb and that was almost impossible to get approval for the
> expense.
>
>And in one PC we needed more drive space.  A 400MB hard drive was
> $1600. Now we cannot even load an OS on a drive that size.

Uh huh, and a 40Gb drive is now $62 at tcwo.

-- 
Cheers, Gene
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
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by Gene Heskett are:
Copyright 2004 by Maurice Eugene Heskett, all rights reserved.



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