Re: What is the difference between core memory and RAM (long)

["Dr. P. Sriram" <sriram@xxxxxxxxxxxxxxxxxx>]

dear luggies,

i am sure many of you know the answer to this - for those who dont (maybe,
even for those who do), core = ram. the term core is used purely for
historical reasons. core memory stands for a type of memory that was the
state-of-the-art sometime about the 70's. ibm was a leading proponent of
this technology. semiconductor memory (sram, dram whatever) was not yet in
a usable state then. core or magnetic core memory used little donut shaped
(i guess i could say polo mint shaped) pieces of magnetic core with lead
wires threaded through. these core pieces were quite small, reaching sizes
small enough to go through the eye of a needle. i remember my friend and
colleague ramakrishna showing me a magazine article with a picture of a
thimble holding thousands of cores (i was not as much of a computer buff
those days and i could not understand what ramakrishna was all excited
about!) a large array of these could be assembled into a flat frame.  the
direction of current passage could be used to magnetize the core in a
particular way and also to read the existing direction of magnetization. 
this technology made it possible to provide a few kilobytes of memory in a
memory subsystem box roughly the size of todays pc system unit. to
understand what a technology leap this was, it has to be recalled that the
typical high-power desktop programmable calculator of those days had
usually 32 bytes (no missing kilo or mega here; only 32 bytes) of data
space (random access) and perhaps 1/2 a kilobyte (or less) of instruction
(sequential access) space.  suddenly, it became possible to up the random
access space to kilo bytes level. also, magnetic core memory was
non-volatile, so power could be turned off, leaving the program and data
intact in memory, to continue usage another day. iit madras obtained an
ibm 370 system at that time, which ran at an unbelievably fast 8 megahertz
and had a core memory of 1 megabyte. the core memory was no larger than a
couple of godrej almirahs in size.  (for some time, this was the
fastest/best computer in the country).  recalling that unix evolved at
that time, it should not be surprising to note that core meant ram as
opposed to disk storage. since accessing ram and disk required different
techniques, a distinction was made between core and disk memories. the
/proc file system concept is perhaps the last step in obliterating this
difference.

sriram


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