Mike's PCjr Page

After seeing references to the modification of the parallel port sidecar to make it bi-directional, I found Mike's page here:

https://www.brutman.com/PCjr/parallel_port.html

which gives a nice overview of the issue and instructions of how to do the mod (which seems very simple).

I'm not entirely clear, though, on what specific uses would benefit from the mod. For example, I have an original, stock parallel port sidecar on my PCjr, and will be connecting a Micro Solutions backpack 3.5" disk drive to it soon. Would reads from the 3.5" disk run faster if I did the bi-directional mod on the sidecar? If so, any idea on roughly how much faster? Are there other examples of peripherals or uses that benefit the most from this mod?

The standard parallel port can write a byte at a time, but only read 4 bits at a time. So writing to a parallel port device will be 2x faster than reading from it.

Put another way, if you are using a parallel port attached device, you will speed up the time to read from it by a factor of 2 if you do the modification. It's not absolutely necessary, but it's also fairly easy to do.

Thanks, Mike -- that makes it very clear.

Ethernet receives a huge benefit from the mod. Most of the time, you will be adding stuff to your PC from another system. The transfer to the PCjr is almost twice as slower as the transfer from the PCjr. without the mod. A parallel port ethernet adapter like Xircom PE3-10BT works well with the PCjr's parallel port and works much better after the port has been modded.