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  • REX for NEC -- recall for first 10 units. See note below. Firmware needs to be updated.
  • needed to fix some bugs in R4.9, so please visit that page to get latest release. QUAD support not yet implemented, but coming.
 Just about finished QUAD : a 4 bank RAM Module for M100.  A great add on; lets REX users benefit
 from multi-bank operation just like T200 and PC-8201!

  • I am working on R5.0, and also a new version of REX called SuperREX. SuperREX will use 4MB flash chips and will have 3.5 MB of file storage, vs only 0.5 MB on standard REX. Stay tuned!
  • January 25, 2015: Quite a few people have received their NEC version of REX! Thanks for the support! So, what's next for REX? Well, what's coming up is "flashdisk" - an integrated file storage solution. I am working on it now, and I hope to release the Flashdisk feature in Release 5.0. Stay tuned! Honestly I think this is the coolest addition to REX. There would probably be about 500kB of storage typically unused in REX - turning that into file storage is like adding hard disk to a PC.
  • January 11, 2015: Release 4.9 has had some improvements and a lot of testing. Now, REX fixes the Y2K bug in all M100, T102, T200 and PC-8201.
  • January 19, 2014: Well it has been a while, but I have finally released version 4.9 as a beta. This release really adds a lot of functionality that makes REX easier to use, and more reliable. Check back as I will be updating this wiki.
  • January 25, 2013: Hi everyone. Just a quick note to say that I have transitioned manufacturing of REX for all current models from the first PCB design to the second. Electrically they are identical. The second PCB is used for REX2 (which included 128k SRAM) and has the name REX2 silkscreened on it, but...there is no SRAM chip, and they are simply REX. I am updating the installation photos.
  • April 15, 2011: A firmware revision is required to address the T200 problem. This will be phased in for all new product, and will be retrofitted into T200 units already out there. M100/T102 models do not appear to be affected. An up-release to software version 4.8 will be released shortly to address minor bugs.
  • April 9, 2011: a minor bug has been idenfitied with ROM Replacement. The Primary ROM image remains blank after loading an image, so this feature will not work.
  • April 6, 2011: A serious issue has been identified with T200 REX that causes an unstable system after power up. Work around is to always run REXMGR.BA after power up OR switching to a new RAM bank.
  • Feb. 14, 2011: Working on a solution for REX for PC-8201 that is plug and play, and will sit directly on the Option ROM socket. It will work identically to the original REX.
  • Jan. 24, 2011: Happy New Year! Release 4.7 is available now for M100/T102 installs. T200 support is done, and Club100 will be offering T200 REX modules shortly (as soon as I'm done making them). This new software has some big improvements!
  • Nov. 10, 2010: On the 35th anniversary of the sinking of the Edmund Fitzgerald, release 4.6 for M100/T102 is made available on the web. Hmmm ... timing is everthing.
  • Sept 23, 2010: A few months back REX2 was finally put together for M100 and T102. It is available by custom order, please get in touch if you are interested.
  • Sept 23, 2010: 4.6 is out for beta testing. Let's hope this goes well. Some important fixes here, and some feature improvements. Main ROM management is supported now.
  • June 13, 2010: Check out the new info on what do to if you delete REXMGR.BA by mistake, posted below.
  • Sept. 1, 2009: Seems that Business Analyst option rom does not work in T102 for reasons unknown.
  • Aug. 31, 2009: I realize that it may not be clearly stated, but REX is not compatible with any other M100 system that uses LOMEM software. Programs like power dos and PCSG RAM modules that place a basic program in memory typically are in conflict with REX. My apologies if people have had problems.
  • Aug. 7, 2009: ROM Replacement feature is being integrated into REX Manager. Specific M100/T102 main rom images will be required, so I have removed M100.bx and T102.bx from the downloadable rom image .zip.
  • Aug. 5, 2009: An updated image set is online. I stupidly forgot to make Multiplan and Integrated Solutions ROMs impervious to removal detection by the M100 ROM. These 2 roms have "AB" at locations 0040 and 0041 hex. The patch is to place 00 in locations 0040 and 0041 hex. Corrected binaries are now in the file. This should only affect M100, as T102 OS looks for "TC" rather than "AB".

Supported Models

  • Model 100 and Tandy 102 with either REX or REX2
  • Tandy 200 with REX.
  • NEC PC-8201 or PC-8300 with REX3

M100 note

 In Europe and UK, and probably elsewhere, there are newer versions of M100 that have different boards.
 Model numbers are 26-3801B and 26-3802B.
 It isn't clear if REX works in those systems; until I can verify, assume REX does not work in anything
 but a USA/Canada equivalent M100 (meaning it has a Modem, and the custom ROM pinout).

PC-8300/8201 note

 October 14, 2015:  
 For REXNEC purchased prior to Oct14, 2015, I would like to recall those early units for a firmware update.
 There is a defect in this firmware that can cause REX to malfunction and require a rebuild, causing
 loss of all data.
 Please note that Main ROM management does not work on PC-8300 since it has a very different ROM structure.

For Owners

Own REX, need help Getting Started?

REX Quickstart guide

Current shipping software release ---> 4.9! If you are not on 4.9, please upgrade! Visit the Release 4.9 page.

Keep in mind the following-

  • upgrade procedures have changed. Upgrading to Release 4.9 requires a complete wipe of REX memory, and a re-install of all Option ROMs and RAM images.

Click on these links for information on specific software releases - release notes, update proceedure, downloads, new features descriptions etc.

REX Release 4.9

REX Release 4.8 Please update to 4.9!

REX Release 4.7 Please update to 4.9!

REX Release 4.6 Please update to 4.9!

REX Release 4.5 and older release info. Please update to 4.9!

What Is REX

REX is completely plug and play flash memory upgrade for Model 100, Tandy 102, Tandy 200, NEC PC-8201 and 8300 laptops. REX plugs into the Option ROM socket, with no soldering or modifications required and no necessity to open the laptop case.

REX gets it's name by being a cross between my other flash memory device, ReMem, and the original OPTION ROM (RAM) memory card, EXTRAM.

Primary features:

  • REX allows for storage and quick, easy switching between OPTION ROM images. Once the binary software images are loaded into REX, the user can easily jump back and forth between different applications.
  • REX provides the ability to backup and swap working RAM images. At the press of a key, your current RAM contents are saved in REX. Furthermore, you can reload any saved RAM image for use. This creates a library of RAM images, which has a number of uses. This offers an easy way to quickly backup all RAM to flash, or switch between multiple snapshots of RAM. It is like having multiple laptops in the same case!
  • REX includes an interface to TPDD devices (like TPDD, NADSbox, LaddieCon etc) for loading and saving binary images to external storage.
  • REX modifies they way MENU displays the date, effectively fixing the Y2K 'bug'.

In addition, REX is in-circuit, software reprogrammable. That means you can change, patch, or replace an Option ROM image without any special hardware or physically unplugging REX.

For advanced users, REX provides some additional features:

  • REX distinguishes between traditional OPTION ROM software, and alternative OS software which runs from the option rom memory location. This allows for some interesting future capabilities like CP/M or a FORTH based system.
  • REX also supports "Main ROM Replacement". This means that, with the addition of a single wire, the main rom on the laptop may be replaced by a version stored in REX. This allows for flash-upgradeable main ROM images, to support patches, custom Menu and character sets, LOMEM patch, Y2K patch etc. Facility is included to support dual Main ROM images, and the ability to switch between them.

REX is available exclusively through Club100.

REX for NEC may be obtained by contacting me directly. twospruces / gmail

REX Versions

The original REX module was designed for Model 100, Tandy 102 and Tandy 200.

REX installed.jpg

REX2 was a modification of REX, which augmented the 1MB Flash with a 128kB SRAM. The intent was to use this card for CP/M in M100 and T102. REX2 is not supported in T200 or NEC machines.

REX2 in M100.jpg

REX2 in T102.jpg

REX2 - custom REX for CP/M support

REX3 is a modification of the original REX design to accommodate installation in a PC-8201 or 8300. The physical dimensions changed slightly, the pinout is different and notably the ALE signal is not available on the NEC socket (which is a standard 27C256 pinout).

REX3 in 8201.jpeg

REX4 aka SuperREX, in development, is based on a single 4MB flash chip.

Installation Information

REX Hardware Installation

click here for current production REX images and install photos

REX Hardware Installation : T200

REX Hardware Installation : PC-8201 or PC-8300

User Information

REX Manager User Guide

Main ROM Management Feature ***new in release 4.6***

Technical Information

REX Overview PDF

REX Overview

Option ROM Images for Download

Validated OPTROM Images for M100/T102

Validated OPTROM Images for T200

Validated OPTROM Images for NEC

Software Installation of the REX System- It's Easy

In order to initialize the laptop to use REX, you must install the REX system. From a cold restart, power cycle the laptop and then execute the BASIC command

(for M100/T102)


(for T200)


(for NEC)


to install the REX Manager system, which uses the timer hook, CHGET and CHPUT RST7 hooks, and a program visible in MENU called REXMGR.

  • REXMGR contains a short embedded machine language routine that starts the REX Manager software on command, and contains the 2 hook programs. Running this program will always start the REX Manager software.

After REX Manager is installed, issuing those same commands won't re-install the system, but you will be directed to the Active OPTROM image software instead, just like you would expect if you had a normal option ROM installed.

If the REX system should somehow become de-installed (like on a cold restart) simply re-install it by repeating these instructions.

Important Note for First Time REX Installation and Use

IMPORTANT! For brand new REX installations, where REX has been unused, the user must replace the default "backup" RAM image stored in REX, with a real backup image. Simply start REX Manager, move the cursor over the directory entry for "backup", and press <ENTER>. Select <Y> when prompted to "Refresh backup?". This puts a fresh RAM image for your specific machine into that entry.

Compatibility between REX and certain other M100 applications

REX is NOT COMPATIBLE with certain software and devices, where software conflicts arise with hidden .BA programs in RAM, and hooks.



...and other things as well I am sure, are not compatible with REX.

REX is incompatible with other software and hardware due to the following reasons:

  • REXMGR has to be located as the FIRST .BA program in RAM for the embedded ML code to function.
  • REXMGR relies on the timer hook to configure itself, and to enable specific features like QuickMenu and Y2K fix.
  • REXMGR uses CHGET and CHPUT hooks (but only in MENU).

If you own a REX and you are using it with some other piece of internal memory system, in general I would say it is not compatible - it is one or the other.


I would like to thank those that have contributed to the project:

John Hogerhuis - for all his technical support

Philip Avery - for his assistance in coding the MENU functions

Wilson Van Alst - for providing the base TPDD routines

Kenneth Pettit - for VirtualT as this project would not have happened without it

Club 100 and Rick Hanson - for helping to get this gadget out there

and others for their helpful comments and support.