On Fri, 25 May 2007 22:20:56 -0500 (CDT), you wrote: Naturally, I jinxed it by bragging about my success :( The next day, the system wouldn't boot and I could see the FAULT light flicker as the system halted at address 10107. I initially thought disk drive problems again, or the pack got clobbered during swap-out for some reason. However, a little investigating quickly showed that even the most basic ten-word TTY check program would not deposit or run. In fact, when depositing or examining sequential locations I found the address display would increment from 0200 to 0001. 0577 would increment to 0400, etc. So something is wrong with address bit 4. I pulled all the boards from the backplane except the CPU set and it still does it. Now I've got to fix the hardware! Sigh. Meanwhile I have been SIMH-building a new OS/8 image from scratch for two drives. After much struggle I have the RL20 handler installed (which has logical drives R20A,B,C,D; the RL21 handler with R21A-D, and I had to omit the last 20% (the "E" drives on RL2E) because OS/8 can only allow fifteen handlers and space is needed for (at least) the R2SY system handler, TTY, SYS and DSK also... reminds me of Gates' "640K should be enough for anyone". -Charles