Subject: Re: Simplest (practical) file system?

From: Megan <[email-masked]>
Date: Mon Jul 28 00:25:01 2003

>It's a LOT easier (and much more efficient) to just implement an
>allocation map.

But not at all needed if you use a flat, contiguous file system.

And remember, the question was asking for the simplest file
system... and a block/sector/whatever allocation map and the
associated code to handle it is not as simple as one can get.

Not to mention the fact that you need tables of pointers to the
blocks so that a file can be reassembled, or read in order... and
the risks to the whole file if the pointers are lost...

I can't tell you how many RT disks I've been able to recover
from truly bad blocks in the directory by virtue of the fact
that the RT directory structure is so simple...

                                        Megan Gentry
                                        Former RT-11 Developer

+--------------------------------+-------------------------------------+
| Megan Gentry, EMT/B, PP-ASEL   | email: mbg at world.std.com         |
| Member of Technical Staff      |        megan at savaje.com          |
| SavaJe Technologies, Inc.      |             (s/ at /@/)             |
| 100 Apollo Drive               | URL:     http://world.std.com/~mbg/ |
| Chelmsford, MA 01824           | "pdp-11 programmer - some assembler |
| (978) 256 6521   (DEC '77-'98) |  required." - mbg            KB1FCA |
+--------------------------------+-------------------------------------+

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From: Vintage Computer Festival <[email-masked]>
Date: Mon Jul 28 09:13:00 2003

> But not at all needed if you use a flat, contiguous file system.

Sure it's needed, because of the issues that you folks have been
discussing with regards to such a beast.  It's clumsy and cumbersome to
deal with when you delete files or need to increase the size of a file.

> associated code to handle it is not as simple as one can get.

The criteria is "simplest usable" and "practical" filesystem.  I think an
allocation map is more usable and practical, but that's just my preference
having been initially exposed to filesystems with these features.

> the risks to the whole file if the pointers are lost...

That's what FAT and ProDOS does, but I'm not suggesting that.  The
allocation map I'm talking about keeps track of the free/used sectors on
the disk so you don't have to set aside large unused swaths of disk space
for each file.

> that the RT directory structure is so simple...

The approach I initially suggested (linked-list sectors) is very robust as
well.

-- 

Sellam Ismail                                        Vintage Computer Festival
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