Re: Projects that take Commodore computers to 2021

From: Jim Brain <brain_at_jbrain.com>
Date: Tue, 14 Dec 2021 15:08:21 -0600
Message-ID: <2ff94278-9673-590b-94f3-41c5ef135f2d_at_jbrain.com>
On 12/14/2021 8:38 AM, Marc Rintsch wrote:
> On 14.12.21 13:48, groepaz_at_gmx.net wrote:
>> Am Dienstag, 14. Dezember 2021, 13:37:25 CET schrieb Marc Rintsch:
>>> On 14.12.21 11:23, groepaz_at_gmx.net wrote:
>>>> ehrm. USR is exactly the same as PRG and SEQ, the only difference 
>>>> is one
>>>> byte in the directory entry. They werent *that* uncommon either :)
>>>
>>> The DOS treats them the same, but many USR files are not written by the
>>> DOS.  GEOS VLIR files are USR and structured not like PRG and SEQ.
>>
>> And you can do exactly the same with PRG or SEQ (and there exist 
>> program that
>> do). I wouldnt say "many are not written by the DOS" either - do you 
>> have
>> another example than GEOS? :) What GEOS does isnt really "USR files" 
>> either,
>> its just tagging a directory entry with USR - to the DOS those arent 
>> even
>
> Of course you can do that with PRG/SEQ too, but you are not supposed 
> to.  With USR on the other hand I always had the impression those are 
> meant to ”go wild” like GEOS did.  „Inside Commodore DOS“ says „A user 
> file may have the structure of either a sequential file or a program 
> file if it was created by the DOS. It may be structured entirely 
> differently if it was created using direct-access techniques described 
> in Chapter 5.”
>
> If there are USR files on a disk I'm cautious about making any 
> assumptions about the structure unless I know for sure which program 
> has written them/if this is a GEOS disk.
>
> Ciao,
>     Marc 'BlackJack' Rintsch

That was what I remembered.  I guess I assumed that if someone was going 
to all the trouble to make a USR file, as opposed to a SEQ/PRG, they 
wanted some specific non standard format or use case.

The challenge with this list is the balance of answering a question here 
without having to be pedantic about every small detail.  My point was 
that SEQ/PRG files don't enforce any specific container format in the 
file, so you can open one and put whatever format you'd like into it, 
WAV or MP3 or TXT, etc.  I called out USR separately, because I was 
afraid if I did not, someone would immediately question it's exclusion.  
But, except for the trivial use of USR (open 1,8,2,"file,u,w"), I'd 
expect folks to use it in a situation where they wanted lots of control 
over file use/format, and so it actually is a case where the format 
might matter.

I'll concede on the specifics of USR files, but I hope my original point 
takes precedence.  You can use a device that implements PRG and SEQ file 
access to store/load any file format you'd like, as groepaz originally 
noted.


Jim


-- 
Jim Brain
brain_at_jbrain.com  
www.jbrain.com
Received on 2021-12-14 23:03:35

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