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river
Forums Junkie

Location:
Land of Oz
Registered:
June 2004

Re: The Good ol' days of computers

Tue, 18 January 2005 21:36

styler wrote on Tue, 18 January 2005 23:04

i saw ancient memory at my course - grid memory with metal
lines and metal beads that could be charged or read -
now that was awesome!

That's called "core memory". It was used on the older style (60's-70's) mainframe computers and some mini-computers of the same vintage. Some companies, like Intel, dabbled a little with this type of memory and called it "bubble memory".

It worked by magnetizing the little metal ring. Each time the memory was being read it would destroy the magnetism so the system had to have a "sense" line that told it the ring was indeed magnetised before it was read. If this happens, after the data is read the system has to remagnetise the ring again.

Usually there is a large metal plate, that is earthed, that goes over the top of the ring matrix to prevent unwanted or spurious spikes that can change the memory. I used to program and repair Data General Nova mini-computers and the memory board was 15 by 15 inches and had a grand total of 4K core memory. Core memory also retains its status when powered-off, so you don't lose your data in a power failure.

Modern dynamic memory chips are similar in that when the data bit is read it drains the capacitor charge and needs to be reset if required. Furthermore, dynamic memory requires constant updating - called refreshing - to maintain its data. Hence the term "dynamic". Between the CPU cycles the memory controller chip scans the entire memory row & column addresses and checks each bit. If it was a "1", it then refreshes the bit 'cos all the little bits are merely baby-sized capacitors that can hold a charge for a very short period. If it ain't refreshed before it's charge vanishes then you lose data. Dynamic memory loses its data when power is lost.

I think that's enough techno and historic babble from Uncle River today Smile

seeyuzz
river

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