It turns out that 5V chips are becoming harder and harder to find, especially in larger sizes.

You can probably see where I’m going with this–I designed a bigger ROM SIMM!įirst of all, I had to find NOR flash chips that ran on 5V and were big enough. After taking into account the 512 KB ROM size, that would leave 7.5 MB of usable space for a ROM disk. Each address points to 4 bytes of data, which provides for a total maximum ROM SIMM size of 8 MB. However, A0 and A1 are unused due to the fact that the data bus is four bytes wide, so there are really only 21 usable address pins. The 64-pin ROM SIMM slot has 23 address pins labeled A0 through A22. It boots up extremely quickly!Īfter he came up with that brilliant idea, I figured I should maximize the potential size of the disk image. It works perfectly and allows you to create a 1.5 MB bootable ROM disk to append to the 512 KB IIsi ROM. However, bbraun came up with an even better idea - a ROM disk driver! He has patched the IIsi ROM (which should be compatible with the SE/30, IIx, IIcx, IIci, IIfx, and of course the IIsi itself) to enable booting from a ROM disk that uses up the remaining space on the SIMM and also has some other tweaks like disabling the slow RAM test that the previously-listed machines perform on every cold boot. I always figured that the 2 MB size of the SIMM was plenty - I never really envisioned using the custom ROM SIMM for anything other than customizing the startup chime. The combination is pretty nifty and enables people to do all kinds of crazy things that previously weren’t possible. Everything from the hardware design to the firmware is completely open source.

Get gfortran-4.2.3.dmg (the GNU Fortran compiler) from r./tools/ and follow the standard installation.These SIMMs (and programmers) are available for purchase here.Īs you may have seen from my previous posts, I have developed a programmable ROM SIMM for older Macintosh computers and a programmer to go with it. To download this you need to sign up as an ADC member, but if you already have an Apple account (e.g. Follow the standard installation (this means that it will install itself when you click on it, and you just need to click to accept a few defaults). you need Xcode to have the installation of gfortran be right, and you need gfortran to make NetCDF).ĭownload the Apple Developers Tools Xcode, from /technology/tools.html, click the Xcode 3: free download link. Note: most of this software needs to be installed in the order given (e.g.

Macintosh roms