RK05 Images
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Roger Smith
Dec 11, 2015, 11:21:33 AM12/11/15
to PiDP-8
Does anyone have any pointers to useful information on the structure of RK05 directories, which blocks do they occupy in the image and what the format of the entries are?
I have a number of RK05 images which look ok in that they are the correct length, but I'd like to look at their directories and the file contents on my desktop before trying to mount them under simh.
Any help appreciated, I'm running linux on the desktop, so Windows or Mac stuff won't be useful.
Roger
I have a number of RK05 images which look ok in that they are the correct length, but I'd like to look at their directories and the file contents on my desktop before trying to mount them under simh.
Any help appreciated, I'm running linux on the desktop, so Windows or Mac stuff won't be useful.
Roger
Rick Murphy
Dec 11, 2015, 6:21:26 PM12/11/15
to Roger Smith, PiDP-8
OS/8 File structure is pretty arcane.
From the OS/8 Software Support Manual:To maintain records of the files on a device, OS/8 allocates blocks 1 through 6 of each file structured device as the file directory.
Entries in this directory inform the system of the name, size, and location of each file, including all empty files and the tentative file, if one exists. For a detailed description of the entries in the file directory, see Appendix A.
Note that "blocks" are 256 12-bit words long (512 six-bit bytes long).
Blocks 1 through 6 on all file structured devices are reserved for the
file directory of that device. Six blocks are always allocated,
though all are not necessarily active at any given time. To minimize
the number of directory reads and writes necessary, OS/8 fills one
directory block completely before overflowing onto a second block.
Thus the user with only a few files can perform directory LOOKUPs and
ENTERs faster than one with many files.
The directory blocks are each structured according to the following
format:
ENTRY
+--------------------------------+
0 | MINUS THE NUMBER OF ENTRIES |
| IN THIS SEGMENT |
+--------------------------------+
1 | THE STARTING BLOCK NUMBER |
| OF THE FIRST FILE IN THIS |
| SEGMENT |
+--------------------------------+
2 | LINK TO NEXT SEGMENT-ZERO |
| IF NO NEXT SEGMENT |
+--------------------------------+
3 | FLAG WORD-POINTS TO LAST WORD |
| OF TENTATIVE FILE ENTRY IN |
| THIS SEGMENT |
| DIRECTORY SEGMENTS ARE ALWAYS |
| LOADED INTO LOCATIONS 11400 |
| TO 117777 BY THE USR; THIS |
| POINTER IS EITHER 0 OR BETWEEN |
| 1400 TO 1777. |
+--------------------------------+
4 | MINUS THE NUMBER OF |
| ADDITIONAL INFORMATION WORDS. |
| THE NUMBER OF ADDITIONAL |
| INFORMATION WORDS SPECIFIED |
| MUST BE THE SAME IN ALL |
| DIRECTORY SEGMENTS |
+--------------------------------+
5 | BEGINNING OF FILE ENTRIES |
+--------------------------------+
. | |
. ~ ~
. | |
+--------------------------------+
377| END OF DIRECTORY BLOCK |
(8)+--------------------------------+
A.1.1 Directory Entries
There are three types of file directory entries. They are PERMANENT
FILE ENTRY, EMPTY FILE ENTRY, and TENTATIVE FILE ENTRY. A permanent
file entry appears as follows:
Location Contents Notes
+-------------------------------+
0 | FILE NAME FILE NAME |\
| CHARACTER 1 CHARACTER 2 | |
+-------------------------------+ |
1 | FILE NAME FILE NAME | |
| CHARACTER 3 CHARACTER 4 | | THE FILE NAME AND EXTENSION
+-------------------------------+ > ARE PACKED IN SIXBIT ASCII
2 | FILE NAME FILE NAME | | (i.e., "A" would be 01)
| CHARACTER 5 CHARACTER 6 | |
+-------------------------------+ |
3 | FILE EXTENSION FILE EXTENSION | |
| CHARACTER 1 CHARACTER 2 |/
+-------------------------------+
| |\
| | | N, THE NUMBER OF ADDITIONAL
+-------------------------------+ | INFORMATION WORDS, IS GIVEN
| ADDITIONAL | | BY WORD 4 OF THE DIRECTORY
~ INFORMATION ~ > HEADER. WORD 4 OF THE ENTRY
| WORDS | | IS EITHER 0 OR THE CREATION
+-------------------------------+ | DATE OF THE FILE.
| | |
N+3 | |/
+-------------------------------+
| |
N+4 | MINUS FILE LENGTH IN BLOCKS |
+-------------------------------+
NOTE
If word 3 is zero, the given file has a
null extension.
An empty file entry appears as follows:
Location Contents
+-----------------------------+
0 | ENTRY IS ALWAYS 0000 |
+-----------------------------+
1 | MINUS THE NUMBER OF BLOCKS |
| IN THIS EMPTY FILE |
+-----------------------------+
A.1.3 Sample Directory
The initial directory written when the OS/8 system is built looks as
follows:
A-3
OS/8 FILE STRUCTURES
Location Contents Notes
+----------+
/ 0 | 7776 | TWO ENTRIES
| 1 | 0070 | FILE STORAGE STARTS AT BLOCK 70(8)*
HEADER < 2 | 0000 | NO ADDITIONAL DIRECTORY SEGMENTS
| 3 | 0000 | NO TENTATIVE FILES.
\ 4 | 7777 | ONE ADDITIONAL INFORMATION WORD
+----------+
/ 5 | 0102 | \
| 6 | 2314 | > FILE NAME IS "ABSLDR"
PERMANENT / 7 | 0422 | /
FILE \ 10 | 2326 | FILE EXTENSION IS SV
ENTRY | 11 | 5370 | DATE IS 10/31/70
\ 12 | 7773 | LENGTH IS FIVE BLOCKS
+----------+
EMPTY / 13 | 0000 | EMPTY FILE
FILE < | |
ENTRY \ 14 | 6534 | LENGTH IS 1244(8) (676(10))BLOCKS -
+----------+ THIS IS DEPENDENT ON THE SYSTEM
| | DEVICE USED. 676 IS THE VALUE
~ ~ FOR A DECTAPE SYSTEM
| |
377(8) +----------+
*This leaves room for the OS/8 System
Areas
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Roger Smith
Dec 12, 2015, 6:31:02 AM12/12/15
to PiDP-8
Many thanks to all who helped, I now have enough information to proceed to the next step.
For the terminally curious, what I am trying to do is to work on downloaded RK05 images on my desktop, before trying them out on the Pi. This way I can do basic sanity checks, like :-
Is this in fact an RK05 image?
Are all blocks accounted for - either in a file or in free space?
What are the directory entries - to build up a list of files and lengths (and later hashes to check against a known good list of versions)
And stuff like that. Eventually I'd like to be able to pull a file straight out of the RK05 image and run it through a disassembler to see what it really does.
On a good image you could do most if not all of this, but on my desktop I can do it faster and more thoroughly and don't get stopped by errors.
May or may not work in the end, but it keeps me out of trouble.
Roger
For the terminally curious, what I am trying to do is to work on downloaded RK05 images on my desktop, before trying them out on the Pi. This way I can do basic sanity checks, like :-
Is this in fact an RK05 image?
Are all blocks accounted for - either in a file or in free space?
What are the directory entries - to build up a list of files and lengths (and later hashes to check against a known good list of versions)
And stuff like that. Eventually I'd like to be able to pull a file straight out of the RK05 image and run it through a disassembler to see what it really does.
On a good image you could do most if not all of this, but on my desktop I can do it faster and more thoroughly and don't get stopped by errors.
May or may not work in the end, but it keeps me out of trouble.
Roger
Steve Tockey
Dec 13, 2015, 6:38:44 PM12/13/15
to PiDP-8
A bit of additional info, in case it might be useful. First, yes, blocks 1-6 are directory blocks. As well, keep in mind that files are stored contiguously on the disk. Another tidbit is that block 0 is the boot block on system disks. The boot block will probably be useless gibberish on a non-system disk, but bootable disks need block 0. The OS/8 run time image also sits in reserved blocks on a bootable system disk. If memory serves, it occupies something like blocks 10-77 but don't quote me on that. Just know that some number of blocks on a system disk are allocated to OS/8 system stuff.
An RK05 disk has two "sides" (it's really inner and outer cylinders but it's easy to think of it as being on sides) in OS/8. One side will be known as RKAx: and the other side will be known as RKBx:. An empty RK05 "side" that's not a system disk should have 3192 free blocks on it.
When/if you can access the disks in OS/8, the program FUTIL (File UTILity) is a great tool for poking around the disk image itself. Documentation is available online at: http://www.pdp8.net/os/os8/futil.shtml. I've recovered many an accidentally-deleted file with FUTIL. Just be really, really careful with it because you can also corrupt a directory pretty easily with it if you don't keep an eye on what you're doing.
-- steve
Roger Smith
Dec 15, 2015, 7:57:29 AM12/15/15
to PiDP-8
Yes. I've been tentatively exploring with futil, basically I make a copy of the image under inspection and mount that as a scratch monkey, then when I make a mistake and it all goes pear shaped and runny I can go back, take a fresh copy and make a different mistake this time.
So far I've had OS/8, TSS/8 and ETOS up and running just to check that most of the bits are there, had a little play with Fortran, Algol and Lisp, oh the joys of retrocomputing, more "Forward to the Past" than "Back to the Future", but still you have to admire the fact that they could get a compiler into 4k or 8k.
Roger
So far I've had OS/8, TSS/8 and ETOS up and running just to check that most of the bits are there, had a little play with Fortran, Algol and Lisp, oh the joys of retrocomputing, more "Forward to the Past" than "Back to the Future", but still you have to admire the fact that they could get a compiler into 4k or 8k.
Roger
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