Re: Internal Date Representation (was Re: Year 2000 (or Year 292 BILLION) -- MIDRANGE-L

Hi, Carl:

The AS/400 also uses a 64-bit clock, but the frequency of update is,
if memory serves correctly, once per 40 microseconds, or 25,000 times
per second.

FWIW.  :^)

I haven't seen the feature, though, where the clock can be manipulated
as you describe.  Interesting.  But how does that help with Y2K 
testing?  Wouldn't you just set the date, and be done with it?

Thanks.

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Carl Friedberg* carl@comets.com <FRIEDBERG on 09/10/97 05:27:03 PM
To: MIDRANGE-L <MIDRANGE-L@midrange.com> @ INTERNET
cc: FRIEDBERG <FRIEDBERG@esb.com> @ INTERNET 
Subject: Internal Date Representation (was Re: Year 2000 (or Year 292 BILLION)

I know,  this is IBM/AS400 territory, but since the topic is interal
date format, I'll throw it in and let the list readers hit delete...

On the DEC VAX (and later, the Alpha), the system clock was based on a 64
bit mechanism. The clock itself (the hardware) gets a "tick" each 100
nanoseconds, or 10,000,000 counts per second. Another piece of the
hardware is programmable, so that an interrupt is generated after, say
10 milliseconds; and all software timer queues are processed at this
frequency, including updating the software clock. The software clock
itself is 64 bits, and counts the number of 100 nanosecond ticks since
an epoch date in the 1860's. I personally have booted a VAX, and by
mistake, entered a date at the console (required under certain 
circumstances encountered when debugging interesting drivers) which was
19987, a typo. The operating system booted up fine, just that the
dates printed with a year field of **** (VMS has always used 4 digit
years, since 1975).

One fun aspect of this hardware mechanism: you can load the interval
register with a number other than the default of 100,000, so that
you can make "time" appear to run faster or slower. Yet another way
to test Y2k (or Y3k if you like) compliance...

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