At 09:10 16/09/1996 GMT0BST, Mike W wrote:
>Error Correcting Memory
>
>If this means what it used to mean (which cannot be guaranteed for
>acronyms, especially in computing) it is memory which stores
>additional bits alongside the actual data, in such a way that it is
>possible to correct some errors in the write/read process.
>
>The basic method is to group the bits, typically into a slab of 64
>bits (ie 8 bytes) and then to compute a collection of parity bits
>over sub-sets of the 64 data bits.  These extra parity bits are
>storerd alongside the original data bits.  When the data are read
>back, the parity bits are recomputed and compared with those
>originally stored.
>
>By doing this over enough sub-sets, it is possibile to detect one or
>two bit errors;  however the smart bit is that it is also possible to
>decide which bit is in error for the single bit error.  Since you
>know which bit is wrong, you can correct the error by simply
>inverting that bit.
>
>There are extra costs.  You need an extra byte of memory for every 8
>bytes stored, and you need extra circuitry to compute and check the
>parity digits.
>
>Modern memory is pretty reliable, and my guess is that unless you are
>into very high reliability environemnts (eg direct control of a
>patient life support system) error correcting memory is not likely to
>be worth the extra cost.  You might do better to spend the money on
>MORE memory, and improve overall performance.
>
Thanks Mike, very clear and concise.

So MCS are selling me a server for a terminal?
I've rejected their new quote - total 1500UKP + vat, and asked if we can buy
our own -
1200UKP all in internet ready, and no ####### vat.
Perhaps the moral is that Compaq are just to ####### expensive. Or is the
mark-up for the supplier the problem?

--------------------------
Dr David J Plews
email: [log in to unmask]



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