> From port-vax-owner-clowenst=ucsd.edu@netbsd.org Sat Feb 19 08:37 PST 2000
> Date: Sat, 19 Feb 2000 11:32:25 -0500 (EST)
> From: Megan <mbg@world.std.com>
> To: Dave McGuire <mcguire@neurotica.com>, Johnny Billquist <bqt@Update.UU.SE>
> Subject: Re: RL01 support in NetBSD?
> Cc: port-vax@netbsd.org, Anders Magnusson <ragge@ludd.luth.se>
> Delivered-To: port-vax@netbsd.org
> 
> 
> >. All files must be contigous.
> 
> True
> 
> >. You can only have one file open for writing on the disk at the same
> >  time.
> 
> Not at all true...  When you create a file for the first time, you specify
> the size you need.  This can be
> 	1) A specific size
> 	2) The largest contiguous space
> 	3) 1/2 the largest, or the second largest (whichever is larger)
> 
> If you attempt to write beyond the end of the space allocated, you get
> an EOF indication.  Most of the utilities have the capability of having
> multiple files open for writing at one time -- how else would you expect
> MACRO to produce an OBJ file and a LST file at the same time, and for
> LINK to produce a SAV, MAP and symbol table file.
> 
> When you close the file, it closes to the highest block number actually
> written.  If you want to *extend* a file, you have to go through some
> real gyrations.
> 
> >. The directory is a few blocks at the beginning of the disk.
> 
> True.  Directory begins in block 6 of the disk, and extends to no more
> than block 67.  Directory segments (which contain directory entries)
> are two blocks long each.  So the first segment is blocks 6/7.  You
> can have up to 31 segments.  Other than the primary directory segment,
> blocks 6/7, other directory segments can be used in any order, and so
> they are a linked list.  Each used segment points to the next one in
> the list.  Last has a null pointer.
> 
> >. The maximum file size is 65535 blocks.
> 
> Yes and no... The maximum file size is contained in a 16-bit word, but
> since the maximum *volume* RT supports is 16-bits, and out of this
> comes the boot block, home block and directory blocks, the absolutely
> maximum sized file you could have (and only one file could be on the
> volume) is approx 65467 blocks.
>
> 					Megan Gentry
> 					Former RT-11 Developer

Thanks for the refresher course, Megan.  The only thing I would add to
this is that it is a _much_ easier task to treat an RT11 file system as
a read-only device.  Creating and deleting files, and splitting
directory segments when they get full adds a great deal of complexity.
Not that it hasn't been done before.  :-)

    carl