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Hard Drives Fail

Last week my main machine was off-line due to a hard drive failure.  Over the years I’ve had maybe four drives fail, but this one wasn’t at all obvious as to what the problem was.  My plan was to take the machine to the local Apple store for a diagnosis when suddenly I realized what was probably going on and ordered a replacement.  This is the system that does a lot of stuff, both for business and personal use.  For a week my email, spreadsheets and CAD package were off-line.

This is an older iMac, but $400 for a new 1 TB SSD seemed like a better deal than $2000 for a new machine.  The system didn’t seem to be slowing down but it’s noticeably faster with the SSD.

Fortunately, Apple includes a backup program with their systems so it was easy to recover all my data once the new drive was installed.


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Upgrading Rev 4 SS-50 Motherboards

More NitrOS/9 news, but not great.  If you’re planning on running any interrupt driven OS on our SS-50 rev 4 motherboard, changes need to be made due to one trace being wrong, another trace missing, and three resistors being too little resistance.  I put together a page with the steps needed to upgrade the motherboard to a rev 4A:

Updating a Rev 4 Motherboard

You only need to do this mod if you plan on using interrupts.

As noted on the page, I will do the mods for free if you mail your motherboard.  Turn-around depends on my work load but can usually be done in a day or two, then mailed back to you.

There are no immediately plans to release a rev 5 motherboard so upgrading a rev 4 is the only option for now.  All motherboards shipping in the last few weeks have had the changes applied.


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This board is targeted to 6809 based systems which have a 4K EPROM window from F000 to FFFF.  By default, the EEPROMs included with all our systems are 8K (28C64) because it’s easier for me to stock one EEPROM instead of multiple ones.  The lower 4K is not accessible, and SBUG is in the top 4K.

As some of you know, we’ve been looking at getting a port of OS/9 and while working with the OS/9 experts it was decided that a custom EPROM image with most of OS/9 in it would be a better solution that have 4K of SBUG and then using a lot of RAM for the OS.  I didn’t want to make a customer choose between flashing either OS/9 or SBUG, so it was suggested to make a small add-on board with DIP switches to select which image to load.

Here is that board:

SW1 controls A12 and SW2 controls A13, so by setting them appropriately and with the right size EPROM, this board allows up to four boot images to be in memory from E000 to FFFF.  Since I use 8K EEPROMs, only two images are available, but a customer can also use a 28C128 which allows four images.

The price for this board assembled and tested without an EEPROM is $20.  Kit is $15, and a bare board for $10.  Free shipping in the US, of course.

I can hear your next question: “So is OS/9 available?”

No, but extremely close.  Boisy Pitre and I worked at VCF SE and made a lot of progress.  I made changes to the EEPROM code and Arduino code, as well as to the motherboard to allow everything to work.  He did all the code changes in NitrOS/9 to support the Corsham Tech boards.  I’ve had a preliminary version running for about a month now and it’s very nice.  Boisy is working to get the changes into the official distribution and then it will be available.  In the picture above, SW1 selects SBUG or NitrOS/9 boot… ON is Flex, OFF is NitrOS/9.

Close, very close.