Dual File Structure CD for RT-11

I don't know how many people might be interested, but I have finally been successful in creating a Bootable RT-11 CD which also has the standard ISO file structure. However, the really key point is that none of the files on the CD are duplicated. On the other hand, I am unable to test the CD that I just burned using real DEC PDP-11 hardware since I have never tried very hard to find and successfully test a CD-ROM drive with a SCSI host adapter on the Qbus PDP-11 which is available for such purposes. But, using the Full Commercial Ersatz-11 running under Windows 98 SE, I just did the commands: MOUNT DU0: SCSI0: BOOT DU0: I assume that if I had a suitable real DEC PDP-11 system with a SCSI CD-ROM drive, the exercise would work there as well since I know that others have been successful with an RT-11 ONLY CD that boots on real DEC PDP-11 hardware. Since many of you reading this who don't know much about RT-11 will likely be confused, let me describe very briefly how I started. I first took 4 RT-11 RL02 bootable images or DSK files, each being 20450 blocks long. Since only the first 5000 to 6000 blocks of each file contained useful non-zero information, I reduced each image to the size that did not contain any blocks with all zeros so that all 4 RL02 images would fit into a single RT-11 partitions of 65536 blocks. I then used Nero Burning under Windows 98 SE to copy all 4 RL02 images to a CD which had the standard ISO file structure after which I copied 24612 blocks from the CD-RW to a file under Windows 98 SE: Blocks 0 to 63 - All zeros Blocks 64 to 99 - Standard ISO file structure Blocks 100 to 24599 - The 4 files Blocks 24600 to 24603 - Extra information for the standard ISO file structure Blocks 24604 to 24611 - All zeros The first file from block 100 to block 5192 was the RL02 bootable image for V5.03 of RT-11. There is one technical problem I have not solved - the current test was done with a CD with an image that is identical to a file of 24612 decimal blocks - which is less than one full RT-11 partition. If I am going to be able to use a CD with more than 65536 decimal blocks of files (i.e. more than one full RT-11 partition), I will have to solve one critical problem. I must find a method of preventing any files under the standard ISO file structure from using any CD sectors that fall in the first 16 that start on a multiple of 16384 sectors (of 2048 bytes which is how a CD is written for those users who might not know). These number correspond to the first 64 blocks that start on a multiple of 65536 blocks (of 512 bytes) on a hard disk drive which corresponds to each RT-11 partition. Before I describe the details, note that the method is probably useful ONLY when the CD contains a limited number of large files. This is because the RT-11 directory on the CD must be mostly constructed by hand at the present time. The first step is to create an exact copy of a CD which has been burned with the desired DSK files. This image file can be created using PUTR to specify the exact size plus E11 and RT-11 to copy all the blocks from the CD to the image file. The critical reason that everything works seems to be a rather fortunate use of the mutually exclusive areas by the RT-11 file structure and the standard ISO file structure. While RT-11 requires the first 64 blocks (of 512 bytes) for the boot blocks and file structure, the standard ISO file structure uses the next 9 sectors from sector 16 to sector 24 (of 2048 bytes) which allows the RT-11 DSK files to start at block number 100 or sector number 25. All that is required (from the RT-11 file structure for the RT-11 DSK file that is in the first RT-11 partition) is to copy the RT-11 file structure (ONLY - i.e. just blocks zero to where the directory segments stop) to the start of the image file (which is initially identical to the ISO file structure CD image with the DSK files placed on the CD using standard CD burning software - in my case I used Nero Burning on a CD-RW so that I need not toss the CD). I produced that image file by using E11 and RT-11 to copy the CD-RW image to an existing file under Windows 98 SE. In my test, since I chose the first DSK file which started at block 100, the next step was to add 100 to the starting block number in each directory segment. The final step was to then select the monitor that I wanted to boot and write the correct boot programs into block zero and 2 through 5 of the image file. All of the extra steps were easily accomplished using E11 and RT-11. The following summary probably helps: RT-11 file structure: Blocks 0 to 63, Sectors 0 to 15 ISO file structure: Blocks 64 to 99, Sectors 16 to 24 RT-11 files: Blocks 100 to 65535 for partition zero ISO files: Sectors 25 to end of CD To create an RT-11 bootable CD, I copied the original CD image to a Windows 98 SE file on the hard disk. I then copied did an INIT DU0:/VOLUME under RT-11 after which is copied blocks 106, 107, 108, 109, 110 and 111 to blocks 6,7,8,9,10,11. The SIPP was used to add 100 (144 octal) to the fifth word in blocks 6, 8 and 10. The last step was to use the RT-11 command COPY/BOOT DU0:RT11XM.SYS DU0: I then had to use the "Burn Image" option under Nero Burning to transfer the complete file back to the CD (after I had erased the files of course) since I do not have any software to write just the first 3 CD sectors. One other aspect is also permitted under RT-11. Since every RT-11 directory segment contains the starting block number in the fifth word, it is possible to have the ISO file that is a bootable RT-11 image of some device referenced both by each file AND as a single DSK file starting with a new directory segment at the end of all the individual files. In my actual test example, there were FOUR bootable DSK files under the ISO file structure (within RT-11 partition zero). The first 3 RT-11 directory segments (starting in block 6 of the CD) contained file headers for 206 files. An additional directory segment was then added (manually one word at a time with SIPP) which had an empty area starting at block 100 with sufficient space for the FOUR bootable DSK files. CREATE was then used to set up the file headers one at a time. Obviously RT-11 is being "fooled", but it does work! The net result is that it is possible to use the same files under BOTH the standard ISO file structure AND the RT-11 file structure. While all of the above was done on a Pentium system running Windows 98 SE, Nero Burning, Ersatz-11, PUTR and RT-11, I am confident that other operating systems and software utilities would also be successful. The actual concepts are really very simple. Implementation of the test case did take almost a week since I made a lot of mistakes along the way. But at this point, I could duplicate a second test in a few hours. If there are any questions, I will be glad to answer them. I do have one request. Does anyone know how or if it might be possible to write a program that can take the image of the CD after it is copied to a file on the hard disk and copy all the data to a second slightly bigger file. The key requirement would be that the blocks at multiples of 65536 (where RT-11 partitions start - actually 64 blocks in each of the 20 possible RT-11 partitions) would be left empty. I would imagine that a simple FORTRAN program could do this if the ISO file structure is known since all that would be required would be to change those parameters which specify the sector number where the file starts - AND move the associated file up in the CD image in the destination file so that 16 sectors starting at multiples of 16384 sectors are left empty. Sincerely yours, Jerome Fine -- If you attempted to send a reply and the original e-mail address has been discontinued due a high volume of junk e-mail, then the semi-permanent e-mail address can be obtained by replacing the four characters preceding the 'at' with the four digits of the current year.