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README.2ND
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README.2ND
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File: README.2ND RT-11 DISTRIBUTIONS V5-0
This CD of RT-11 distributions holds twenty-four binary RT-11 distributions
for V05.07 and prior. In addition, this CD contains RT-11 file structures
along with the normal ISO9660 file structure. Individuals who have access
to hardware and software which can read the CD correctly (in an emulated
512 byte block file format under either a real DEC PDP-11 or an emulated
PDP-11) will be able to BOOT V05.03 of RT-11 directly from this CD.
Although this CD is probably not unique in having two file structures, it
is probably one of the very few in which the files are NOT duplicated. The
actual contents of each file are present on the CD only ONCE. While most
users will look at only the ISO9660 file structure, all of the file entries
within the four RT-11 file structures (one is required for each 32 MByte
RT-11 partition and each have exactly 65536 blocks) point to the same
location on the CD insofar as each file is concerned.
If an image file of this CD is being used (probably under an emulator), the
image file should ALWAYS be used in a READ ONLY mode. Each of the three
bootable RT-11 partitions contain file directories which cover the bootable
distributions TWICE, first as the last RL02 image followed by over two
hundred files which are contained within that same RL02 image. As before,
the actual file contents are not duplicated. This highly unusual situation
was produced by manually setting the fifth word of the second directory
segment (starting block number of the first file in that directory segment)
back to the actual block number where the file (SWAP.SYS in this case)
begins within the RT-11 partition (RT-11 does not try to check the value).
Although a limited set of changes might be possible for those experts who
are fully aware of the potential disaster which any changes might produce,
it is strongly suggested that none are likely to be worth the attempt.
In order to be able to boot any given distribution of RT-11, a standard
set of requirements must be satisfied. The only aspects which will be
discussed in this file are those which are added to the standard set due
to the use of a CD (or, as in probably most cases, an image file of the
CD being used with an emulator) which started as an ISO9660 set of files
of RL02 file images.
One aspect of booting which may not be appreciated is that RT-11 is able
to boot and run from a system device which is READ ONLY. While it is
obviously essential to be able to write any permanent changes to a drive
which allows a write operation, under RT-11, the operating system does
not require any device, and in particular the system device, to be able
to accept a write operation during any normal RT-11 process. Thus, unlike
some operating systems, RT-11 can be run from either a CD or an image file
of the CD which is READ ONLY.
However, it was necessary to perform a write operation to the MSCP device
drivers, DU(X).SYS, prior to booting RT-11 from the second and third RT-11
partitions (PART=1 and PART=2). Those write operations were made using an
image file of the CD until testing was complete. If any further changes
are deemed essential in the future, a copy of the image file for the CD
should be made to test that the changes will not cause any difficulties
before they are applied to the original image file of the CD.
Page 1
File: README.2ND RT-11 DISTRIBUTIONS V5-0
The next requirement for the CD was to set up the RT-11 file structure
for each RT-11 partition, as per the statement at the beginning of this
file. There is one ISO9660 file structure which starts at block 60 or
CD sector 15. Under RT-11, the file structure for each RT-11 partition
of 65536 blocks (the only size which RT-11 allows and only MSCP devices
can have partitions) starts at block zero and uses a maximum of 68 blocks,
although a user option easily restricts the maximum to 60 blocks.
Consequently, the location of the ISO9660 file structure and the RT-11
file structure for the first RT-11 partition (PART=0) do not overlap.
But, there was a problem with the rest of the RT-11 partitions and their
RT-11 file structures. In addition, the "Nero Burning" software, which
was used to set up the ISO9660 file structure, copied all files to the CD
in order of the file name without any ability to avoid selected sectors
on the CD. Rather than try and overcome this aspect of the order and
location of the files by "Nero Burning", the solution that was adopted
was to incorporate empty spacer files at the end of each RT-11 partition
along with one empty spacer file, EMPTY.FIL, at the beginning of the CD
immediately following the ISO9660 file structure. The size of EMPTY.FIL
was chosen so that the next file, README.1ST, would start at block 256
on the CD which is CD sector 64.
Once that decision was made, the size of the next empty spacer file,
RTV5RL.03S, was straightforward. The previous 20 files on the CD occupy a
total of 56648 blocks and start at block 256. In order to force RTV5RL.04
to start at block 65536+68, RTV5RL.03S must be 8700 blocks. The sizes for
the other two empty spacer files, RTV5RL.06S and RTV5RL.07S, were determined
in a similar manner.
A test CD was initially produced to determine the correct size of the
first empty spacer file, EMPTY.FIL, so that README.1ST would start at
block 256. For this version of the CD, EMPTY.FIL is 152 blocks.
The next step was a bit unusual, but relatively simple. Under RT-11,
SIPP.SAV was used to add an additional directory segment to the one
existing directory segment at the start of each RT-11 partition. This
was necessary because the files used when RT-11 is booted must be in the
file structure of an RT-11 partition whereas, at that point, they were
only in the file structure of the subset file. The directory segment
had to be added with SIPP since the starting block number would overlap
the last file already on the RT-11 partition. That allowed the files to
be "copied" (for a second time - they were actually already there inside
the subset - the starting block number of the second directory segment
was chosen to make sure that the "copies" occupied the same blocks as the
original files). Now the file structures for the bootable RT-11 partitions
contained the individual files from the bootable RT-11 distributions.
Once the files were "copied", an RT-11 command was used to set up the boot
blocks on each of the three bootable RT-11 partitions:
COPY/BOOT DU0:RT11XM.SYS DU0:
However, DU1: and DU2: required one additional step. Each of the files
DU.SYS and DUX.SYS from the bootable distributions had to be modified using
the eight RT-11 commands:
Page 2
File: README.2ND RT-11 DISTRIBUTIONS V5-0
SET DU0: UNIT=0, PART=0
SET DU1: UNIT=0, PART=1
SET DU2: UNIT=0, PART=2
SET DU3: UNIT=0, PART=3
SET DU4: UNIT=0, PART=4
SET DU5: UNIT=0, PART=5
SET DU6: UNIT=0, PART=6
SET DU7: UNIT=0, PART=7
However, if performed on the files which were part of the actual RT-11
distribution, they would be changed inside the subset. The solution
was to rename DU.SYS and DUX.SYS to DU.DEC and DUX.DEC, respectively,
then make new copies of DU.SYS and DUX.SYS immediately after the subset
and alter the new versions. In practice, the same procedure was also
performed for DU0: since otherwise, it would not be possible to access
DU1: and DU2: from DU0: and boot the V05.06 and V05.07 of RT-11. Once
the names were changed within the file structures for the RT-11 partitions
(for the files actually located inside the subsets) and the new versions
copied to locations following the subsets (within the empty spacer files),
the COPY/BOOT commands could be done. And since the name changes were
made only in the RT-11 file structures for the RT-11 partitions, not in
the file structures for the subsets, the three subsets themselves are
totally unchanged and remain an exact pristine copy of the original RL02
image file.
After the initial CD was produced and copied to a container file on the
hard drive of exactly four RT-11 partitions (134,217,728 bytes), the next
step was to set up the file structures for the four RT-11 partitions for
the files that were in each RT-11 partition. In actual practice, exactly
the opposite was done since after the CD was produced, each of the four
RT-11 partitions were already positioned in that container file with only
the ISO9660 file structure missing. After those few blocks were copied
(from block 60 to block 103 on the image file of the CD), the basic
structure was complete.
Although the above explanation sounds reasonable, in practice it took
several weeks to accomplish. It is now possible to boot three different
distributions of RT-11 on each of the three bootable RT-11 partitions.
The modified files DU.SYS and DUX.SYS are at the very end of each RT-11
partition. Fortunately (actually chosen because it was possible), V05.06
of RT-11 was the first version which could be booted from a non-zero RT-11
partition. And of course, the MSCP device drivers, DU(X).SYS were only
available starting with V05.00 of RT-11 and RT-11 partitions only first
available with V05.03 of RT-11. If everything seems to have worked out
rather well with this CD, it is because it was planned that way.
One final point. The first two files under the RT-11 file structure are
IS9660.DIR with 44 blocks and EMPTY.FIL with 152 blocks for a total of
196 blocks. The total blocks for these two files will remain constant.
Future versions of this CD will include sub-directories for the ISO9660
file structure and a larger IS9660.DIR file. EMPTY.FIL will be decreased
by the same number of blocks as the size of IS9660.DIR increases. This
will keep the starting block number for README.1ST at block number 256.
Page 3