[alt.folklore.computers] Re: Memory
Brian Inglis
From: "Jack Peacock" <pea...@simconv.com>
Newsgroups: alt.folklore.computers
"Erno Palonheimo" <e...@theremin.hut.fi> wrote in message
news:uthr900...@theremin.hut.fi...
> "g.g.coombes" <g.g.c...@ntlworld.com> writes:
>
> > I have a pc66 and i thinks the memory chips are sdram dim
> > Can anyone tell me of this is right. i have no idea about computers,so any
> > advice would be nice.
>
> No. They're ferrite core memory, your local computer dealer quite
> likely has some of that in stock.
>
That's right, the "PC66" stands for Perkovskite Core 66 (66 cores per
nanometer) as opposed to the newer 100 cores/nm and 133 cores/nm type
memories. These are the newer, more advanced solid state core memories
where the toroids were replaced by Perkovskite crystals. Be sure to ask
for the CAS/2, or Core Addressing Strobe 2 microsecond, versions. This
is the critical timing for the write pulse that recovers the data stored
in the magnetic field. It's not so well known that a write pulse slower
or faster than 2 usec will cause flux stress in the core and eventually
cause it to crack, so be sure to specify the 2 usec CAS strobe time.
You need not worry about the RAS, Rewrite Addresing Strobe, as this will
automatically occur synchronously to the initial write (hence the tern
Synchronous memory). However, as always be sure to install the Faraday
cage around your memory once it is in place on the motherboard,
otherwise you will be susceptible to electro-magnetic pulse bit errors.
Naturally you will want the DIMM (dual inline magnetic modulator) wired
versions. Unlike the SIMM (single inline magnetic modulator) of older
designs the DIMM has two wires, one for the write pulse, and a sense
line to return the magnetic field polarity. The older SIMM memories
only had one wire running through the ferrite/perkovskite cores and had
to multiplex write pulse/sense line functions. DIMMs double the access
speed by eliminating the MUX timing cycle so the memory can be
written/read/rewritten at the same time.
Whatever you do, do not try to use RAMBUS (Radio Active Magnetic Bubble
Un Shielded) memory. Only properly certified technicians can install
this type of core memory. When used with CPUs clocked over 1GHZ the
radiation emitted from improperly installed RAMBUS can exceed 500
millicuries/hour. Any wonder there are so many lawsuits involving
RAMBUS?
Any PC store should be able to supply all these types of core memory.
But make sure the tech gives you the right sized Faraday cage to go with
the parts (SIMM cages are extruded brass, DIMM cages are braided copper,
and RAMBUS cages are solid lead). The manufacturer supplies this free
but many unscrupulous dealers will pretend not to know what the cage is,
so you will have to return for a service call months later, after the
warranty expires.
Good thing you asked in the folklore group where oldtimers had to learn
all the intricacies of magnetic memories. A lot of people will try to
tell you that memory is made out of silicon, which of course is absurd.
Ever try to find the north (1) or south (0) bit on a grain of sand?
(Note I used the northern hemisphere equivalents, as we all know south
of the equator all bit polarities flip.)
Jack Peacock
"Why is my hair falling out?" last words from a do-it-yourself RAMBUS user
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