Collections, was: Be careful handling computer racks

I would suggest that you aim a bit higher at a BA23 box since they are probably just as available as a PDP-11/03 as far as the backplane is concerned. MegaByte memory should also be available, so the minimum CPU would be a PDP-11/23. V05.00 of RT-11 supports the use of the full 4 MegaBytes of the memory and is available. SCSI hard disk drives are relatively rare, but probably inexpensive. The older drives of less than 10 GB are no longer seen very often. However, I have a number of (very?) noisy 2 GB drives I rarely use. The host adapters are still expensive. The alternatives are ESDI or MFM drives. ESDI controllers may be less available. The RQDXn controllers from DEC should be more available. Since you are mostly a hardware person (if you want a Heath 11), what do you actually do with a computer after you have it running? I ask that since I am a software person. There seems to be an endless supply of software challenges once the hardware is working. 8" DS/DD floppies are probably rare. HOWEVER, before I found a supply, it was possible to punch the additional index holes in the cardboard jacket to enable DS use. The media are identical as far as I could ever tell. You may want to cover over the SS index hole. I probably have a few 8" DS/DD floppy media, but they have software on them. Which 8" DS/DD drive do you use? The DSD 880/30 combination was the only drive that I ever used that was 8" DS/DD. Also, which operating system? In RT-11, the DY.SYS device driver works very well. BUT the DYX.SYS device driver supports ONLY an 18 bit address, so the user buffer MUST be below 1/4 MegaByte in the extended memory for the DEC release. Since all of the DEC utility programs avoid the use of extended memory, a user buffer above 1/4 MegaByte is a problem only if VBGEXE is being used with a DEC utility program. Sincerely yours, Jerome Fine