This page describes the configuration of my TRS-80 Model 4 (Gate Array version) and its conversion to operate with:
- One real single-side floppy drive (rather than 2 drives)
- One Gotek floppy-drive emulator running FlashFloppy firmware
- One FreHD hard-drive emulator
I will be building out various sections of this page from time to time, to document the above modifications (which have already been made and are working fine, as at January 2026).
My notes below primarily relate to using LSDOS/LDOS on the Model 4. Other DOS’s (such as CP/M) can also be used on the same hardware, but their setup and use are not documented on this page.
Physical and electronic configuration
The FreHD that I am using was purchased from Jay Newirth as part of a “GOTEK/FREHD COMBO DRIVE SLED (LOADED)” package in June 2025, which I have installed as the upper drive in the Model 4. The lower drive is a standard TRS-80 full-height, 40-track, single-sided floppy drive. I have installed a switch (and selectively wired pins 10, 12 and 14 of the 34-way connector at the Gotek and the floppy drive) so that either drive can be “Drive 0”, with the other drive automatically becoming “Drive 1”. This allows either the Gotek or the physical drive to be the boot device.
The combo sled from Jay is a very neat unit. The only issue I had with it is that one of the mounting legs for the Gotek (part of the 3D printed sled) had busted off during transit to Australia, even though it was bubble wrapped and protected inside a cardboard box inside my checked luggage. I’ve repaired it with epoxy glue, but perhaps this part of the design could do with strengthening.
The FreHD connects to the 50-way expansion edge connector underneath the Model 4. Because my machine is missing the RF shield over the main board, I was able to run the cable down the component side of the main board, and then out through the case slot for the 50-way edge connector. Power for the FreHD was obtained by picking up some unused pins on the Model 4’s internal power supply.
Getting the FreHD up and running
There are 2 ways of booting the FreHD on a Model 4:
- Using a sysgen’d boot floppy disk to bring up the FreHD as the system drive. With this approach, no ROM change is required. If you want to change DOS’s (say from LSDOS to LDOS or NEWDOS/80), you’ll need a different boot floppy and a different SD card. The boot floppy can be in a physical floppy drive or in a Gotek, provided the appropriate drive is wired to respond as “Drive 0”
- Installing a modified ROM in the Model 4, so you can boot to FreHD without needing a boot floppy disk. With this approach you don’t even need a working floppy drive. A really nice thing about this approach is that you are presented with an on-screen menu to select one of several DOSs (all of which simultaneously exist on the SD card) making it a very elegant multi-boot system. Some wiring changes are needed to accommodate the new ROM however, as the pinouts (and number of ROM pins) on the new ROM are different from the original TRS-80 ROM
Both of the above approaches require that your FreHD is fitted with an SD card that contains the appropriate emulated hard-drive file(s). The second approach also requires that the file “frehd.rom” is on the SD card, so it can be brought into TRS-80 memory and executed as part of the boot process. With the first approach, the only file that needs to be on the SD card is “hard4-0”.
From this point onwards, this page relates the first of the two above approaches, namely booting FreHD with a boot floppy disk, as at this stage I want to leave the Model 4 as original as possible, and have not studied what (if any) the downsides are of changing the TRS-80 ROMs.
FreHD hard drive images
Original Version
The PIC firmware on the FreHD expects the SD card to contain a file called “hard4-0” with no filename extension. If a second virtual hard drive is used, it expects that to be called “hard4-1”. So far as I’m aware, the LDOS/LSDOS configurations only use a single virtual hard drive and expect that to be called “hard4-0”.
When I purchased my first FreHD from Ian in 2013, I received a CDROM. It had 3 instances on “hard4-0” on it. They all appeared to contain LSDOS 6.3.1 based on examination with Hex Editor Neo. The first file is in the upper levels of the directory tree (in the “Vecoven” directory). It’s a 12.9MB image and won’t boot with the supplied LSDOS boot floppy disk. So I haven’t done anything further with this image. The other two images are both 40MB in size and are in the “LSDOS images” subdirectory. One is zipped and one is unzipped. They are identical 40MB binary images (once the zipped one in unzipped!) and both boot with the supplied LSDOS 6.3.1 boot floppy disk. You can download the zipped image and its directory listing here:
Here is a copy of the ZIP’d “hard4-0” image, and a copy of its directory listing (made once the image is booted):
“hard4-0” from “LSDOS images” directory on 2013 Vecoven CDROM
Short directory listing of above “hard4-0” image made using the “DIR(P)” command
Long directory listing of above “hard4-0” image made using the “DIR(P,INV,SYS)” command
Modified Version
Back in 2013, I modified that original version as follows:
- Moved the 5 FreHD utilities from Partition HARDB to Partition HARDE
- Installed LDOS 5.3.1 on Partition HARDB (so this image can also be booted under LDOS 5.3.1)
- Deleted all the files from Partition HARDC (which seem to be related to the LESCRIPT program)
- Installed what appears to be the RSHARD1 package on Partition HARDC. I’m not sure why I did this. Perhaps it was when I was experimenting with the FreHD on a TRS-80 Model 1
- Installed 26 games on Partition HARDF
The process I used to carry out these modifications was described on an older version of my website that no longer exists. But here is a copy of the page from that defunct website -> Dual Booting FreHD on TRS-80 Model III and Model 4.
This modified “hard4-0” can be booted under LSDOS 6.3.1 on a Model 4. It also can be booted under LDOS 5.3.1 on a Model 4 (in Model III mode) and on a Model III. All of these configurations have been tested on real hardware, as well as on the trs80gp emulator. In each case, you will need an appropriately configured (sysgen’d) LSDOS/LDOS floppy disk to boot the system with, and these are available (and discussed) in the following section of this page.
Here is a copy of my modified “hard4-0” image, and a copy of its directory listing (made once the image is booted):
Modified “hard4-0” image that I modified in 2013
Short directory listing of above “hard4-0” image made using the “DIR(P)” command
Long directory listing of above “hard4-0” image made using the “DIR(P,INV,SYS)” command
FreHD boot floppy images
Here are 4 floppy disk images for booting LSDOS 6.3.1 or LDOS 5.3.1 using the above-mentioned “hard4-0” hard-drive images. The LDOS 5.3.1 images will of course only work with the modified version of hard4-0. The LSDOS 6.3.1 images will work with both versions of hard4-0:
- LSDOS 6.3.1 Floppy Boot Disk for FreHD in DMK format: This is Sysgen’d so that after booting from the floppy drive, the hard drive will be the system drive, and the floppy disk can then be removed. I believe this originally came from Ian Mavric in 2013 (as an un-labelled blue physical floppy disk), though that version was a 41-track disk and I have deliberately now imaged it as a 40-track image. The modified image works fine both on my real Model 4, and with the trs80gp emulator. This image can be written out to a real floppy drive using a Catweasel board (using dmk2cw) or using Greaseweazle (using dmk2gw)
- LSDOS 6.3.1 Floppy Boot Disk for FreHD in HFE format: This is identical to the above image, but in hfe format. Use this version if you want to boot the FreHD from the Gotek drive (rather than booting from a physical floppy drive). Place it on the USB stick that you use with your Gotek/FlashFloppy setup
- LDOS 5.3.1 Floppy Boot Disk for FreHD in DMK format: This is Sysgen’d so that after booting from the floppy drive, the hard drive will be the system drive, and the floppy disk can then be removed. This was generated by myself in 2013 per the notes I refer to above in the description of “hard4-0”. This image can be written out to a real floppy drive using a Catweasel board (using dmk2cw) or using Greaseweazle (using dmk2gw)
- LDOS 5.3.1 Floppy Boot Disk for FreHD in HFE format: This is identical to the above image, but in hfe format. Use this version if you want to boot the FreHD from the Gotek drive (rather than booting from a physical floppy drive). Place it on the USB stick that you use with your Gotek/FlashFloppy setup
The above DMK images have been tested on my real Model 4, and with the trs80gp emulator in both Model 3 and Model 4 modes. The HFE images have been tested on my real Model 4.