[HECnet] The new few centuries (or DATE75)

[Paul Koning]

> On Dec 31, 2020, at 5:45 PM, Robert Armstrong <bob at jfcl.com> wrote:
> 
>> Thomas DeBellis wrote:
>> So I went spelunking and here is what DATE75 is all about.  
>> Briefly, very early versions of Tops-10 could only handle dates between January 1st 1964 and January 4th 1975 ...
> 
>  The DECtape directory format (on TOPS-10) used only 12 bits to store the date, and between 1964 and 1975 are 4096 days.  

I thought maybe you meant the DOS-11 DECtape date problem, but that hit in 1974.  The reason is also 12 bits, and the fact that date is encoded (as it is on RSTS) as (year - 1970) * 1000 + day.  So somewhere in April 1974 the date would wrap.  Fixed, on RSTS at least, by changing it to 15 bits, since the next higher 3 bits were unused on RSTS.

I was in college when this happened, and I remember diagnosing the issue and sending the patch to DEC.  :-)

	paul