The IMSAI SIO 2 Rev-3 is a faithful reproduction of the 1975 SIO USART board.
The SIO 2 is available in a one-port (SIO 2-1) or a two-port (SIO 2-2) configuration.
Each port is a complete synchronous/asynchronous USART (8251A) with TTL, RS-232, and current loop interfaces.
A port expansion kit is available to convert an SIO 2-1 to an SIO 2-2.
When built to the instructions in the new User Manual,
the SIO 2 is electrically and mechanically identical to the 1975 IMSAI SIO 2 Rev-3.
Order one from the list below. The kits are complete with everything you need except solder and tools unless otherwise stated.
They even come with a nice printed user manual. Be sure to hover over any
icons for more information.
| Description | Part Number | Availability | Unit Price (USD) |
SIO 2-1 Rev-3 complete kit with manual  | SIO 2-1-R | 6/30/2025 | $229.00 |
| SIO 2-2 Rev-3 complete kit with manual | SIO 2-2-R | 6/30/2025 | $249.00 |
Most builders won’t need anything else besides one of the above complete kits.
To skip over the options go to More Information to get links to useful resources.
If you're an advanced builder and want to see all the options, read on.
| Description | Part Number | Availability | Unit Price (USD) |
| MIO, SIO 2 internal cable, 26-pin card edge to DB25-F | CABLE A | 6/30/2025 | $40.00 |
| Port expansion module for SIO 2-1 Rev-3 | SIO 2M-R | 6/30/2025 | $30.00 |
| Socket set for SIO 2-1 Rev-3, standard | SOC-SIO 2-1-R | 6/30/2025 | $9.00 |
| Socket set for SIO 2-1 Rev-3, machined | SOCM-SIO 2-1-R | 6/30/2025 | $28.00 |
| Socket set for SIO 2-2 Rev-3, machined | SOCM-SIO 2-2-R | 6/30/2025 | $35.00 |
You may order a bare printed circuit board for you to use your own parts.
Be advised that individual parts are not available to bare board customers unless they are explicitly in the parts list below.