The Altair 8800C Project

For this project, I wanted something more closely aligned to the original Altair 8800 computer systems from the 1970s. It turned out that others have also had a similar dream and over time have created a number of boards and hardware solutions to achieve a system that is being called the Altair 8800C in some circles.

The Altair 8800C is not an 8080 emulation or clone that uses an Arduino, Raspberry Pi or some other form of a modern processor to emulate the Altair 8800. The Altair 8800C uses a real 8080 microprocessor running on a reproduction MITS, REV-1 CPU board at its heart. It is a fully functional Altair built entirely from new equipment and boards that first became became available in 2018.

A hybrid computer like this one, mixing new and vintage equipment, allows the computer to serve as a reliable platform when working on vintage or designing new S-100 boards.

The Altair 8800C is as close as it gets to having a vintage Altair 8800 in ones personal retro computer collection without having to pay the high prices being received for the classic ones on Ebay or other such site.

The Altair 8800C is not really a kit as of yet.  You can not buy it all form a single source. Nor is it based on a single design concept. I needed to pick how I wished to build out my system. The range can be from a "keep everything as vintage as possible" to building one using many modern parts. For my Altair 8800C, I went with sourcing as many modern components that support the operational feel of the original Altair 8800.

Below is what I came up with for my Altair 8800C.

The Altair 8800C Cabinet

The cabinet I select is also the cabinet used by Mike Douglas for his Altair 8800 Clone computer. He now also offers the cabinet for Altair 8800C builds. This custom designed cabinet by Mike has a look that is very close to the original Optoma cabinet use by MITS and works well for a Altair 8800C design.

While the original Altair 8800 front panel board will now work in this case, Mike is also offering a set of boards that provide, what I feel is a much better solution. Refer to the front panel section below for more details.

The most resent batch of cabinets now have added pre-drilled holes that supports a 9-slot motherboard or two of the Altair 4-slot motherboards. I still needed to drill holes to support my selected power supply solution and card guides though.

Inside the Altair 8800C cabinet

A look inside my cabinet reveals my decision to use modern switching power supplies. This is definitely not in alignment with the original heavy linear power supplies that where available back in 1975. Given the Altair clone case being a much lighter constitution then the original Optoma case used by MITS, the more efficient and much lights weight switching power supply seemed to me a better fit for my 8800C.

There is also the much higher 80% plus efficiency of modern switching power supplies verse the 40-50% of the older linear deigns of the day.

In my design I uses three switching power supplies to power the Altair 8800C. The larger plus 9-volt DC can supply up to 10-amps. A pair of smaller units support plus and minus 16-volt DC up to 2-amps each. A standard NEMA 5-15P line cord is used to connect to the US 115-volt AC mains power. A 1.5 amp, slow blow fuse is in line to protect from over current. The main power switch is located on the front of the Altair 8800C. I placed the high voltage wiring in to black plastic Split-Loom for added protection. This cable is routed around the cabinet to the Molex connector that plugs into the isolated section of the front panel board supporting the AC power switch.

Cooling is provided by the more efficient 120mmx120mmx25mm 5-volt DC fan. Again a change for the original 120-volt AC fan used in the original Altair 8800. Given the selected fan is 5-volts, a small DC-DC converter is used to convert the power from the 9-volt DC supply down to the 5-volts DC need by the fan. The fan draws about 0.5 amps of current from the 10-amps available on the main 9-volt switcher.

The Card Cage

For the motherboard I went with a nine slot version of the N8VEM S-100 backplane version 4 available through Todd Goodman. See  if you with to obtain one for your self. This motherboard has the additional advantage of being supported by my selected cabinet.

I am not using this motherboard's active termination option. All the S-100 connectors are passively connected. I only populated the nine S-100 connectors, the 6-pin Molex power connector, the three power monitor LEDs and their supporting current limiting resisters.

The two light blue card guides on each end of the motherboard, are custom designed and 3D printed off my Wanhao Duplicator i3 Plus. I have made both the right and left card guide files available at the Tinkercad web site. To find the two files, use the show me (search) and enter Altair 8800C.

The CPU Board (Reproduction)

For the CPU board, I went with a MITS Altair 8800 reproduction CPU board created by Gery Kaufman. This reproduction board used and original 8080 based, MITS REV-1 CPU board as a source. This reproduction follows the original board layout very closely. You even use the original 1975 Altair 8800 CPU assemble manual to build up this board. More information can be found at Gery's web site at

All the parts used on the board where soured through a veritiy of vendors like Digi-Key, Jameco Electronic and some form Ebay.

The Front Panel Interface Board

Interfacing all the LEDs and toggle switches found on the front panel of the classic Altair 8800 design is accomplished on my Altair 8800C using a set of boards designed and provided by Mike Douglas. More information is at his web site.

In the picture above we see the S-100 interface board used in the two board set. This design is a great improvement to the original Altair's many wire harness used to connect the front panel to the both the S-100 bus and CPU board.

In Mike's design, there is only a 50-pin ribbon cable that connects the S-100 interface board to the front panel board and an additional 8-pin bridge cable that runs between the CPU board and the font panel interface board. The S-100 interface board is plugged in to the next S100 slots next to the CPU board. This allows the 8-pin bridging cable to connect the two board together.

From an operational point of view, the new front panel design seems to keeps all the original functionality, complete with the Altair's original quirks.

The two board set is provided as raw boards with only the pre-programmed PIC processor and a few spacers supplied with the boards. The remainder of the parts where easily sourced through Digi-Key and Mouser Electronics.

The FDC+ Board

For floppy drive support, I went with the FDC+ board by Mike Douglas. This neat board allows many options in interfacing a variety of floppy drives types to your Altair 8800 system. The FDC+ is a 100% compatible drop-in replacement for the original Altair FDC solution. There is even support for the use of virtual serial drives where a modern Windows system is setup with a drive server application and through a high speed serial connection to a special connection to the  FDC+. With this setup, you are able to map up to four floppy drive image files to act like physical drives. The following is a table of drive TYPE options supported by the FDC+:

Type 0 - Original Altiar 8" drive

Type 1 - Direct connect to Shugart 8" (or similar) drive looking like a Altair 8" drive

Type 2 - Original Altair Minidisk

Type 3 - Direct connect to 5 1/4" drive looking like a Altair Minidisk

Type 4 - 5 1/4" soft-sector floppy drive looking like a Altair 8" drive

Type 6 - Serial drive looking like an Alair Minidisk

Type 7 - Serial drive looking like an Altair 8" drive

There are also some nice extras also supported on the FDC+ board. A 27C64 EPROM socket is also supported. A pre-programmed EPROM with a disk boot loader (CDBL), the Altair multi-boot loader (MBL), the Altair turnkey monitor (TURMON) and an Intel hex loader comes installed in the EPROM socket.

You also receive three adapter boards that convert the 50-pin connector on the FDC+ board to support the DB-37F connector used on the Altiar 8" drives, an IDC-26 adapter for the Altair Minidisk drives and an IDC-34 adapter for standard 5 1/4" floppy drives. None of the adapter boards come with connectors, so you will need to order whatever is need your your system.

Finally there is support for up to 64K of static RAM on the FDC+ board. The RAM space is configurable to be placed in most any range needed to back fill any extra RAM needs or to be the only RAM used within the Altair 8800.

Mike ships the FDC+ board fully assembled and tested but remember you will need to buy any parts for the adapter boards. You simply drop the FDC+ board in to an open S-100 slot on the Altair 8800 type system, configure it for you needs and your are off and running. For more information visit Mike's site at .

The 88-2SIOJP-R100 Board

For serial input/output, I went with the 88-2SIOJP-R100 board by Marton Eberhard. This board provides hardware to support dual serial ports that are fully compatible with the original MITS 88-2SIO serial interface board. For more information check out

In addition this board also adds a socket to support one 2716 EPROM or 2816A EEPROM with write capability if a EEPROM is used.

Jumper selectable power-on/RESET jump start to an address is also supported. This version of jump start is compatible with memory boards that does not support S-100 phantom signals.

Jumper selectable automatic EPROM disable to allow access to a full 64K of system RAM.

Improved power-on clear circuit that eliminates the need to toggle the RESET switch on the Altair 8800.

This board comes fully assembled and test. There are two version when ordering this board. The R100, like the one I ordered, is populated with two standard 26-pin headers that the use of two DB-25 ribbon cable assemblies. If you desire the classic Molex connectors found in the original MITS 88-2SIO board, you need to order the M156 option.

Full Altair 8800C System Running

Here is my finished Altair 8800C system up and running. While there are still some details I need to complete in the areas of floppy drive power supplies and other peripherals, the core system is working.