[cctalk] Re: 5150 mobo?

IIRC, there were two main models of 5150, and a few sub-models. All 5150 were five slot. (5160 (XT) had 8 slots) There was the "16-64KB" that had one row of 4116 soldered in, and three rows of sockets. It could be purchased with those other three rows populated, at a rather high price for 4116s, or could be purchased with those three rows unpopulated. Both Apple2 and TRS80 used 4116s, so the competition had driven the prices way down. Similarly, the Tandon TM100-1 disk drive was available very cheap in the TRS80 after-market. So, the cheapest way into a 5150 was to buy a minimal system, an FDC board, and a CGA video board, and provide your own 4116s, TM100 drives, and a composite monitor. At Merritt College, we had had a PDP11, with an aftermarket drive, being used for not much more than teaching FORTRAN and COBOL. The second time that the machine was down for most of a semester, the college sold it to the Richmond School District (now "West Contra Costa"), and put a few doaen 5150s in its place. While far from comparable, there were never times when there wasn't a computer available for Fortran, COBOL, and then also BASIC. When Richmond installed the machine, something "went wrong", quite likely confusion about delta vs Y three phase power. The official (coverup) story was a "lightning strike" (at that time of year??!?), and PG&E paid for a replacement machine. S, everybody got what they needed. The 5150s were picky about the RAM. Some types of RAM chips would not work in it, although would work fine in Apple, or "memory tester"s. At one point, the college bought some RAM from Fry's, that did not work. But, at the Fry's store, they retested it and insisted there was nothing wrong. We escalated. Fry himself came up to Oakland to bring RAM chips that worked on our 5150s. Then, there was the "64-256KB" motherboard. It had one row of 4164s soldered in, and three rows of sockets. Populating those with 4164s gave you 256K of RAM. BUT, there was an empty socket on the board, that you could populate; I don't know whether it was a PAL or some 74xx logic, that then let you use two rows of 4164s (one row of which was soldered in) and two rows of 41256, giving 640K! 640K was all of the RAM that could be easily used, other than some upper memory space of the other video or bits in between other stuff. We sometimes referred to the two types of motherboards as "16K" and "256K" to lessen ambiguity. -- Grumpy Ol' Fred cisin(a)xenosoft.com