Altair 8800 Clone

The Altair 8800 Clone is a full size, fully functional replica of the computer that started a revolution – the Altair 8800. Whether used for personal or educational purposes, the Altair Clone is a great way to relive this important period in computing history and learn core computer science principles at the same time!

The Altair Clone provides an accurate, hands-on experience without having to worry about damaging a vintage computer. Built with modern hardware on the inside, the Clone is also less expensive and much easier to keep running than a vintage computer.

System Overview

From the operator's perspective, the Altair 8800 Clone accurately duplicates the look, feel, features, performance (and limitations!) of an Altair 8800. Software designed to run on a typical Altair 8800 will run on the clone in the same manner and at the same speed as on the original Altair.

The Altair 8800 Clone accurately duplicates the operation of an Altair 8800 equipped as follows:

• CPU – 8080 running at 2 MHz.
• RAM – 64K of RAM with memory protect in 256 byte blocks.
• ROM – Eight "sockets" provide up to 16K of ROM. RAM is replaced by ROM in 256 byte increments.
• Serial I/O – Two external RS-232 serial ports are provided. The ports are wired to DB-25 connectors on the rear of the computer. The serial ports can be configured in numerous combinations of 88-2SIO and 88-SIO serial ports. The optional Audio Cassette Interface provides a third serial port and rear panel DB-25 connector.
• Printer I/O – The 88-LPC (Okidata) Line Printer Controller was a common printer interface supported by Altair BASIC and CP/M on the Altair. Output to the 88-LPC can be routed to one of the serial ports on the rear of the Altair Clone.
  
  The 88-C700 (Centronics) printer interface is also supported through one of the Altair Clone's serial ports. This printer is required to run newer Altair software like Timesharing BASIC and the accounting system.
• Cassette I/O – The original 88-ACR cassette interface included an 88-SIO board for serial I/O. One of the Altair Clone's serial ports can be configured as the 88-SIO board used with the cassette interface. This, in turn, allows any software using the cassette interface (loading BASIC, loading and saving BASIC programs, etc.) to function normally by exchanging cassette data at RS-232 levels with a PC. For a more realistic Altair experience, add the optional Audio Cassette Interface which duplicates the functionality of the original Altair 88-ACR Audio Cassette Interface and connects to a standard audio cassette recorder.
• Disk I/O – Three Altair floppy drives and controller (e.g., the 88-DCDD) are implemented using non-volatile storage inside the Altair Clone. The Altair floppy's data transfer rate, sector index rate, track stepping rate, controller registers, etc., are all accurately duplicated. Boot ROMs, Disk BASIC, Altair DOS, CP/M, etc., all operate as if connected to original Altair floppy drives. A connection to a PC is required only to "insert" a new floppy disk. Other than that, a PC connection is not required. Since the drive content is non-volatile, the floppy disk content will be present anytime you power up the Altair Clone without having to re-connect to a PC.
  
  In addition to the Altair 8 inch floppy, the 5.25 inch Altair Minidisk floppy drive and controller are also emulated.
• Interrupts – The 88-VI/RTC vectored interrupt and real-time clock board is implemented in the Altair 8800 Clone. This board can be used to prioritize interrupts to the 8080 processor from the vectored interrupt lines (VI0 - VI7) on the Altair bus. The board also provides real-time clock interrupts if required. If the board is not enabled, then the default interrupt structure of the Altair (PINT with RST7) is used. Interrupts are generated in the Altair Clone by both serial ports (2SIO and/or SIO), the floppy disk controller, the real-time clock, and the 88-C700 Centronics printer interface.
• Turnkey Module – The Turnkey board from the Altair 8800bt Turnkey computer can be "installed" in the Altair 8800 Clone. In addition to providing sockets for 1K of PROM and a 2SIO style serial port (both already present in the Clone), the Turnkey board also provides auto-start at a specified address on power up or front panel reset. The Turnkey board also allows PROM to overlay RAM so that a full 64K of RAM is available even with PROMs installed.

Want to know more? Listen to this interview with Mike Douglas, creator of the Altair 8800 Clone, by David Greelish, computer historian. You can also visit the Details page to learn more about the design and creation of the Altair 8800 Clone.

If you'd prefer to build a "real" Altair 8800 with a functional S-100 bus, consider pulling together the parts to make the Altair 8800c.