MITS ALTAIR 8800 #2

Micro Instrumentation and Telemetry Systems (MITS) ALTAIR 8800

This system was donated by George J. Roy. It was purchased as a kit, and assembled by George.

Serial Number 223482K. The "K" at the end of the serial number usually means that it was sold as a kit. From the date codes on the boards, it looks like this system is from early 1976.

The MITS Altair 8800 was designed in 1974 by Ed Roberts and Bill Yates at MITS in Albuquerque, New Mexico. It is based on the Intel 8080 CPU and the backplane is the S-100 bus. The Altair was featured on the cover of the January 1975 issue of Popular Electronics, and was sold by mail order. The designers were surprised when they sold thousands of the kits in the first month. Altair BASIC for this machine was the product that caused Microsoft to really grow.

This system has had the Grounding Modification performed that connects Logic Ground to Chassis Ground in many places. It has the earlier multiple 4-slot backplanes.


We need to find Micropolis MDOS and Micropolis Extended BASIC on diskettes for this system

To boot MDOS from diskette:
Set the address switches to F400
Press RESET, EXAMINE, and then RUN


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This system originally came with an 88-ACR Cassette interface board, so it came with BASIC on Cassette. The 2400/1850 refers to the modulation frequencies used to represent ones and zeros. These are the later frequencies that were used after March 1, 1976 and have more separation between the two frequencies for better reliability.

These four RAM boards were included with the Altair donation. We will install some of them in the other Altair.

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A Godbout Econoram VII 24k RAM board
It is populated with 4k x 1 static RAM chips arranged in 2x 4k and 2x 8k blocks
The first 8k block is set for addresses of 0000-1FFF
The second 8k block is set for addresses of 2000-3FFF
The first 4k block is set for addresses of 6000-6FFF
The second 4k block is set for addresses of 7000-7FFF
This board can read, but not deposit when in Altair #1 using the front panel

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A PSS RAM8 8k board
It is populated 1k x 1 bit static RAM chips
It is set for addresses of 4000-5FFF
This boards works OK in Altair #1 using the front panel

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A Quantronics MM8 8k Static RAM board
It is populated 1k x 1 bit static RAM chips, and it looks like one chip was replaced
It is set for addresses of 8000-9FFF
This boards works OK in Altair #1 using the front panel

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A MITS 4k Static RAM board
It is populated 1k x 1 bit static RAM chips
It is set for addresses of A000-AFFF
This boards works OK in Altair #1 using the front panel

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It would be nice to know where this serial number falls in the production range.
The "K" at the end of the serial number means that it was sold as a kit.

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The boards from the Right to Left are:
  • MITS 8080 CPU
  • Tanner Computers 64k Static RAM
  • MITS 88-2 Serial I/O
  • Micropolis Floppy Disk Controller

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The inside without the boards installed
You can see the early design 4x slot backplanes
The 33,000 uF capacitor for the +8V supply is much larger than the original

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The Revision 1 CPU Board

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Tanner Computers 64k Static RAM
This is set with RAM at 0000-EFFF and F800-FFFF
Part of the missing address space from F000-F7FF is used by the floppy controller

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MITS 88-2 Dual SIO board
The I/O Address is configured for 020-023
Port #0 is configured for RS-232, 1200 baud
Port #1 is configured for RS-232, 300 baud and has CTS & DCD connected to ground
On the Molex SIO connectors the pinout is:
  1. CTS to DB25-5
  2. DCD to DB25-8
  3. RTS to DB25-4
  4. Ground to DB25-7 and DB25-20
  5. N/C
  6. N/C
  7. Receive to DB25-2
  8. Transmit to DB25-3
  9. N/C
  10. Ground

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The Micropolis 1071 Floppy Disk Controller set to address F400-F7FF
The boot ROM occupies F400-F5FF, and the controller occupies F600-F7FF

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The Micropolis 1023-II Disk Storage Module
This should have terminator resistors installed and be jumpered for drive 0
The diskettes have 16 hard sectors, 77 tracks at 100TPI, and hold 315kB
The later industry standard diskettes were 96TPI
This unit is jumpered for unit #1 and does not have the terminator resistors installed.
I changed the jumper to unit #0, and will find a terminator DIP to install later.
I need to make a longer 34 pin cable to connect the drive to the controller.



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