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Re: My IBM PS/2 model 35SX build

Thanks for the write-up, that was fun to read! Beautiful machine. I have a 76i that has the same case, but is a MCA machine with a 486DX. What do you plan to run on it? And do you have a socket for a cpu ugrade? There is a wealth of upgrade possibilities to turn your 386 in a half decent 486 😀

Re: 486 MB frequency

The standard 486 and 486DX pin doesn't have a CLK2 pin (which is named that way, because it receives two times the clock speed). A CLK2 pin is present on 286, 386 and some special early low-power 486 chips. The ordinary 486 processor has a CLK pin instead and expects the actual processor clock at …

Re: 486 MB frequency

The frontside bus frequency of 33 MHz povided by the mainboard is doubled inside the CPU. So it effectively runs at 66 MHz. DX2 stands for "x2". After a lot of fiddling I found that it is a bit different. In your case the socket receives the 50MHz from the crystal, this goes to CLK2. In a normal ' …

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