skr@nvuxh.UUCP (Steve Reinhardt) (12/13/88)
I have a Sperry PC/IT (286 machine) with 512K on the motherboard and I'd like to have 640K under MSDOS. There are sockets for 18 more 256K chips (for a total of 1M) on the motherboard. However, in the section on setting the DIP switches to configure memory in the system installation manual, it is implied that with 1M on the board you can either choose: 1. 1M mapped from 0-1M, giving you 640K under MSDOS and wasting 384K, or 2. 512K from 0-512K, and 512K from 1M-1.5M, giving 512K for DOS and 512K of extended memory. (Yes, I *have* been reading this newsgroup, but if I still messed up on extended vs. expanded, don't flame me. If you don't understand what I mean, hit 'n'.) What I really want is 640K for MSDOS, but I don't want to buy 512K of RAM and only get to use 128K of it. So what's the deal? a) Am I messed up, and the 384K in option #1 is not wasted? (Even if it's only for a ram disk, it's not a total loss.) b) If I am right, can I use smaller (cheaper) chips, like 18 64K chips or 9 128K chips (do they even make 128Kx1 DRAMS?) to get 640K? I'm not totally unwilling to cut & solder, though of course I'd rather not. Another option would be to get just 9 256K chips, and then I'd only be wasting 128K. Please don't write me to tell me "99% of all AT clones work this way", because the Sperry IT is generally in the other 1% in those cases. If you do have experience with the IT, please let me know. Thanks, Steve Reinhardt ...!bellcore!nvuxh!skr or nvuxh!skr@bellcore.bellcore.com (it's ugly, but it works) US Mail: NVC 2Z-135, Bell Communications Research, Red Bank, NJ 07701