If it doesn't have 36 bits, you aren't playing with a full DEC.

KL10 Serial Number 1354

This particular machine was used by MCI/Tymnet in Fremont, California, running TYMCOM-X, their proprietary operating system derived from an early version of TOPS-10 (maybe even back when it was just called "Monitor").

Instead of using the DEC Massbus disk and tape drives more commonly seen on DECsystem 10s, MCI/Tymnet was using IBM bus/tag devices attached via a System Concepts SA-10 Channel Adapter. We were originally told that the processor didn't even have any RH20 Massbus adapters, but fortunately for us it does have one. (DEC probably wouldn't provide field service without at least one.)

The machine was used with an Ampex ARM10 external memory box, which provided four megawords of ECC-protected semiconductor memory (using 64K DRAMs). The ARM10 attaches to KI10-style memory busses via the DMA20 memory bus interface in bay 3 of the KL10 cabinet.


The Computer Museum is concerned with keeping their machine as historically authentic as possible, but Scott and I will probably have to make some compromises if we are to afford to operate the system. We don't plan on making any irreversible changes though.

A standard KL10 processor is rated to consume about 12.6 kilowatts of power, which is about 35A/phase of three-phase 120VAC. Here in California, electricity is fairly expensive, so we won't be able to afford to run the system very much if we can't curb its appetite a bit. Compuserve reportedly replaced the linear power supplies of many KL10s with switching supplies. While I don't have the details of their modification, I plan to do essentially the same thing with our machine.

The ARM10 memory box is big and power hungry, and it isn't really contemporary with the processor anyhow, so it is a good candidate for replacement with a modern memory system.

I'm designing a replacement memory system using a single 4M*36 bit SIMM (or perhaps two 4M*32 SIMMs to provide ECC). Perhaps the new memory board can be designed to plug directly into one of the S-bus slots of the KL10 main CPU backplane, replacing the cabling that normally leads to the DMA20.

Another obvious possiblity for an upgrade would be to build a SCSI interface. This could either plug into a Massbus connector, or actually replace an RH20. A company in Canada made a Massbus to SCSI adapter that emulated RP07s, at a cost of about $30,000. There reportedly were other such interfaces; apparently DEC even resold one.


If you have any spare DEC 10 or 20 please let either Scott or me know. Thanks!

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Last updated November 1, 1998

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