This card is a great solution for older XT machines which are not capable of 640k memory on the motherboard. The original architecture of the IBM XT has 20 address lines which gives a maximum memory space of 1MB. The top 384k is typically reserved for BIOS, leaving the lower 640k available for applications. This board will address the full 1MB address space, and some machines and applications will allow access to the upper memory area. This card has 16 dip switches to allow access to memory in 64k sections, so you can enable and disable ranges as you like. Additionally, you can set the card to allow access above 16k for the original IBM 5150.
Please be aware this card is 8-bit, and not meant for 80286 or greater machines. It is possible it may work in later systems to a degree, but it would cripple performance as the data bus is limited to 8 bits. If your IBM XT or clone already has 640k of RAM, then you do not need this board. If you can upgrade your motherboard to 640k, we recommend that approach instead. It is meant for systems which have a limitation on how much RAM can fit on the motherboard. Many of the original IBM XTs are limited to 64k or 256k on the motherboard making a RAM expansion board essential.
Purchase is for PCB only. Parts will need to be purchased separately, and assembled. The link below contains a full bill of materials to complete the build, as well as the instructions on how to set the board jumpers. We have updated the card to use a currently available off-the-shelf bracket. It is a Keystone 9202 and it uses Keystone 9900 screws, both can found at Mouser along with the other parts.
Lo-tech reference page: wiki page.
The through-hole parts have been changed to surface mount, please note these replacement part numbers for the bill of materials:
|Multilayer Ceramic Capacitors MLCC
|1210 (3225 metric)
|DIP Switches / SIP Switches SPST 8 switch sections