[Info-vax] DEC Multia (UDB) issues

[Johnny Billquist]

On 2011-10-19 08.52, glen herrmannsfeldt wrote:
> In comp.os.vms Steven Schweda<sms.antinode at gmail.com>  wrote:
>
> (snip)
>>    Really?  The oldest/lamest Alpha system I ever used was an
>> AlphaStation 200 4/233.  Its approved memory was fast-page
>> mode, parity.  (According to its "User Information" book,
>> "The system requires 72-pin parity SIMMs that have an access
>> time of 70 ns (nanoseconds) or 60 ns.")  But those extra
>> "parity" bits were aggregated for use as ECC, not for simple
>> parity.  One extra bit for each eight data bits means four
>> extra bits for a 32-bit word, which is enough for ECC.
>
> No, but 8 extra bits for a 64 bit word is enough for ECC.

Right. If I remember right, you need five bits of ECC for 32 bits of data.

Exactly how many bits you need for 64 bits I don't know, but I would 
have suspected that 8 bits would be enough. :-)

	Johnny