[Info-vax] DEC Multia (UDB) issues

[Rich Alderson]

Johnny Billquist <bqt at softjar.se> writes:

> 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. :-)

The KL-10 processor uses 44-bit memory to represent 36 bits of data, with
single-bit correction/double-bit detection.

-- 
Rich Alderson                                   news at alderson.users.panix.com
    the russet leaves of an autumn oak/inspire once again the failed poet/
    to take up his pen/and essay to place his meagre words upon the page...