Date   : Thu, 23 Mar 2006 18:02:59 -0000
From   : "David Harper" <dl.harper@...>
Subject: Re: Web site: Mainly Master 512

David Hunt wrote:


>> >> A curiosity I came across while doing this: You cannot enter dates 
>> >> into
>> >> M512 DOS-Plus earlier than 1980.
>> >
>> > That would make sense - in the disc catalogue (FAT12/16/32) dates are
>> all
>> > stored relative to 1980 (7 bits, thus 2108 is going to be a painful 
>> > year
>> > for
>> > Windows) so you'd want to clamp it to 1980 to stop negative datestamps.
>>
>> Agreed. There is some logic in this.
>>
>> >> However, the date stored in DOS-Plus counts from
>> >> the beginning of 1978.
>> >
>> > That would not make sense,
>>
>> I cannot see any sense in it either, which is why I asked. It is the way
>> the
>> date is stored, however. Look at it if you like. The value (in M512 DOS-
>> Plus
>> 2.1) is a word variable stored at 1197:005F
>>
>
> Perhaps it is a remnant of CP/M i.e. 1-1-1978, isn't DOS Plus a descendant
> of CP/M 86 which in turn is a descendant of CP/M. I'd imagine this was 
> done
> for compatibility with PC-DOS & MS-DOS whose dates start at 1-1-1980. ???

You could well be right here. DOS-Plus certainly is an offspring of CP/M-86. 
It uses a lot of CP/M code at low level. It is supposed to be compatible 
with both CP/M-86 and MS-DOS, but in its structure it is really CP/M-86 with 
MS-DOS compatibility tacked on.

David Harper