I have a trs-80 model 100. I have all the option rams used. I've seen some quite useful ideas from other collectors on the internet for other TRS-80 model computers of using mouser electronic parts to create peripherals.

So it should be possible to create a custom rom chip that supports 4 MB of ram. Something like Re-mem?

I know that some assembly language is going to have to be put into work and already found an open source assembler from another enthusiast on sourceforge for the model 100.

I found out that its possible to create a custom Linux Kernel for the specific hardware. I can more conveniently use a stripped down Unix clone from sourceforge for the z80 type processors.

A text based bootable Linux custom rom chip is possible. So any ideas to get a custom blank rom chip(with 50 mb for packages) would be useful. If not I'll have to do a long research project.

1 Answer 1


Your question isn't very clear. If the question is "Would it be possible to design a memory expansion module for the Model 100 that adds large amounts of additional memory?", then the answer is yes.

The Model 100 has its system bus exposed on the expansion connector. It would certainly be possible to design a memory expansion that adds a memory window to the 8085's address space. With bankswitching, the amount of additional RAM or ROM is effectively unlimited. Software would have to be modified to be made aware of the bankswitched memory.

The hardware could be quite simple. A register to store the current bank. A few logic gates to decode addresses. A few logic gates to decode writes to the bank register. One or more SRAM or EEPROM chips. Some buffers.

This method has been used for memory expansion on many 8-bit and 16-bit systems.

I'm not quite sure what you mean when you refer to Linux in your question. Linux will not run on the 8085. Linux requires a 32-bit processor and many megabytes of RAM with flat addressing. With enough RAM you could theoretically write a program for the Model 100 that simulates a processor that can run Linux, but in practice it would be uselessly slow.

  • Linux requires a 32-bit processor? At least FuzixOS uses 8-bit.
    – Polluks
    Commented Mar 26, 2019 at 11:29
  • @Polluks Linux requires a Memory Management Unit, which Intel introduced to their 32-bit 386. (Hence no Linux for 286 and earlier.) My impression is that Fuzix is more akin to Minix or Unix than it is to Linux.
    – Kaz
    Commented Mar 26, 2019 at 13:23
  • @Polluks Well, Fuzix would be the best bet.
    – The T
    Commented Mar 26, 2019 at 14:14
  • @Polluks FUZIX is not GNU/Linux. It's a very, very stripped down Unix clone, most similar to Unix v7 from the late 1970s.
    – RETRAC
    Commented Mar 26, 2019 at 15:30
  • @TravisWells FUZIX requires rather specific memory mapping hardware to be properly useful. It might be possible to cram a single user non-multitasking version into the Model 100, but multiple 16 KB banks and an interrupt timer are almost essential.
    – RETRAC
    Commented Mar 26, 2019 at 15:32

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