Olivetti M20

Hi Gene I would suspect that the one on eBay isn't ready for CP/M8000 right out of the box. I'm sure it'll handle PCOS, at least version 2.0f. The problem is that most machines didn't come with enough memory for CP/M8000. Although, the manual for CP/M8000 states that one can run in a machine with 128K of memory, because of a number of allocation issues in the M20, you really need 384K. The M20's comes with 128K on the mother board and usually have two 32K expansion memory cards. Even with three of these 32K cards, your only up to 224K. Still not enough. When I first got CP/M8000 running on my machine, I modified two of my memory cards to take 64K DRAM chips. This brings it to 384K. I was always going to increase it to 512K, the most that the M20 decodes, but I don't see the need any more. A fellow in Italy had thought that it might be easier to take two 1 meg simm's and use those ( you need at least 2 because it does access 8 bit or 16 bit and needs the separate selects ). We talked it over and came up with a way to wire them up such that they can provide 384K with a minimum of external hardware( total of 512K with the mother boards memory). The only painful issue is that the M20 normally has a select for either 32K or 128K at each board position. The first solution used three board edges to connect the two other connectors selects. Another fellow built one that he made a header to go under the NAND gate chip that normally sent out the selects. This did require lifting one part and putting it on a socket. It also seems that some of the memory boards came with sockets and could be configured for either 32K or 128K by jumpers but none of my board were that easy. There are two main memory board types. One is for B/W monitors while the other is for Color. The only difference in the systems to run color is the expansion memory cards. The color cards had a parallel to serial shift register added to be used for the color bits rather then the memory mapped DMA that the B/W monitor used. For color, depending on how many memory expansion cards one had, one could have 2,4 or 8 colors. The video takes 16K from each card. It doesn't cause holes in the memory map because the M20 had a PROM to map the physical memory into specific locations in the logical memory. They did one other thing that was different than done on other machines. It decodes intruction memory different than data memory. This is part of the reason it can't have the full memory that the Z8000 would otherwise be able to address. It did have the advantage that for the setup for some of the segments, one could address 128K at one time ( 64K instruction space and 64K of data space ). This meant that this instruction space needed to be mapped into some other segment as data memory or one couldn't write to that space from disk. This causes confusion for those working with the debugger or looking at how the images are loaded from disk to memory for these dual mapped physical memory areas. Who ever gets the unit on eBay, make sure to have them send the monitor. It uses some unusual vertical and horizantal rates that may not be easy to find in other monitors. Dwight _________________________________________________________________ Fixing up the home? Live Search can help http://imagine-windowslive.com/search/kits/default.aspx?kit=improve&loc…