5MHz Upgrade hacks

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Can we speed up the Model T? Apparently!

I have been investigating various ways to make the Model T run … faster.

Initially, I started with fixed 5MHz upgrades. These are practical if you never ever want to run at 2.5MHz. But, since 5MHz operation effectively renders the cassette port unusable, a switchable design might also be nice. Switchable means that you can control the speed from BASIC.

Switchable solutions

In the M100/T102, port /Y1 is free to use. So, for switchable implementations

  Power up default is 2.5 MHz
  OUT144,0   sets to 2.5MHz
  OUT144,1   sets to 5MHz

Current Upgrades Status

Computer model Fixed 5MHz Switchable 5MHz
T102 V1.1 PCBs, instructions available PCB available
M100 V1.1 PCBs, instructions pending PCBs available
M100 (UK) like M100? like M100, but no need for new EPROM
M100+NSC800 contact me -
T200 not yet investigated not yet investigated
PC-8201 not yet investigated not yet investigated
KC-85 like M100? like M100?

As I test and more-or-less land on a reasonable upgrade process, I will post instruction files here If you have any questions, please get in touch with me at Twospruces at --the google mail service.

Also, since OSHPARK is so clumsy in dealing with PCB revisions (basically you can't remove a bad file design once shared), I've decided to just post PCB gerber files and schematics here. That way I can control issues that I find and always have the corrected files available.

What are the tradeoffs?

A fixed solution makes your laptop always run at 5MHz. A switchable solution gives you the option of standard operation or "TURBO mode". The switchable solution is a nice way to go. Switch up when needed, switch down when necessary.

Some of the considerations are captured below.

Laptop functionality

Item Fixed 5MHz Switchable 5MHz
Processor speed 5MHz 2.5 or 5 MHz
LCD 5MHz 2.5 or 5 MHz
I/O 5MHz 2.5 or 5 MHz
BCR 5MHz 2.5 or 5 MHz
Cassette assumed non functional functional in 2.5 MHz mode
Modem standard standard
Printer standard standard
Power consumption ~50% higher ~50% higher in 5MHz mode

Complexity of modifications

Item Fixed 5MHz Switchable 5MHz
Clock PCB assembly ease easiest small SMT soldering
Crystal location swap onboard mounted on adapter board
Clock PCB installation ease easiest additional wiring
M100 ROM upgrade challenging to build challenging to build
M100 main PCB cut tracks? one clock trace one clock trace
T102 main PCB cut tracks? one clock trace and RAM mod one clock trace and RAM mod
Reversible? yes, remove hack and repair cut tracks yes, remove hack and repair cut tracks

What about compatibility with REX#/REXCPM?

REX# and REXCPM from November 2021 are built and tested compatible with 5MHz. In fact my test station runs at 5MHz. If you have an earlier REX#/REXCPM, contact me to discuss what to do.

What do you need?

  Some hardware skills - soldering, PCB modification etc.
  a clock divider circuit board
  a small number of parts (depending on the solution)
  a 9.803 HC49 crystal


Take a look at the instruction files below. Please don't try this if you are not confident of success! I welcome feedback and comments. Especially if you find errors or improvements.

Fixed 5MHz Upgrades

Computer model Version Upgrade file
T102 Fixed 2x upgrade V1.1 T102 5MHz mod V1.1 Nov 2021.pdf
M100 Fixed 2x upgrade V1 M100 5MHz mod V1 Apr 2022.pdf

For M100 with NSC800, contact me for a solution. This would of course be a dedicated CP/M machine with REXCPM installed.

Switchable 5MHz Upgrades

Computer model Version Upgrade file
T102 Switchable 2x upgrade V1 design is done. working on docs
M100 Switchable 2x upgrade V1 design is done. working on docs


Posted here so I can maintain and update the designs, are Gerber files, layout images and schematic images.

PCB Version Comments Gerbers Schematic and layout images BOM
Fixed 5MHz clock board This board has no small SMT and uses main board crystal. Easiest! V2 tbd tbd tbd
Switchable 5MHz clock board, simplified larger board, easier to install V3 tbd tbd tbd


T102 with a fixed 5MHz board. This board is easy to make, and the 10M crystal is on the main board. No small SMT soldering! Note: what is shown is an early board. Latest board is more compact and eliminates the unused parts.

T102 fixed.jpg

T102 with a switchable 5MHz board. This board has to use a crystal on the clock board, and has small SMT soldering. Harder to build, but has switchable clock.

This board is good, but there is a better solution.

T102 switchable.jpg


As this is tried I'm sure questions and comments will arise. We can capture useful information here. Thanks.