The most important part of this step is that you write the files as “Renamed MIDI files.” I typically name each one with the name of the track, and make sure each name starts with the track number (00, 01, 02…). This makes it much easier to keep track of which MIDI file goes with which MP3 later on.
Using PPFBU to extract the files, and then export them as Renamed MIDI files. I’m using a dedicated Windows XP box that I keep just for this purpose. You can rename the files in PPFBU before you export them, or you can rename the MIDI files after (like I did in this case).
Ripping an Audio CD using Asunder on a Linux system.
Name and Organize the Files
Below, you can see the files listed after ripping the audio CD, and after backing up the floppy disk drive using Player Piano Floppy Backup Utility. The floppy disk tracks are MIDI files and have a .mid extension. These contain the instructions to operate the piano. The CD tracks have been ripped as MP3 files and therefore have a .mp3 extension—these contain the audio.
All the files are present, but they will not yet play correctly in the Disklavier, as the filenames do not match.
I wrote a short Python script to automatically rewrite all the filenames to match. Using the numbers at the beginning of each filename, it pairs together matching MIDI and MP3 files and names them whatever the name of the MIDI file is, but without spaces or symbols. This appears to be the same formatting of downloadable Disklavier albums.
Whether you use the script or not, the before and after directory listings indicate how you must rename the files.The script is called using the following syntax:
Note that now the MP3 and MIDI files have identical names for each song, identical capitalization, and that all spaces and symbols have been removed. In the ENSPIRE, unlike earlier iterations of the Disklavier, filename length does not seem to matter. Here’s a graphical representation of the last folder, ready to move:
The filenames match! It’s ready to be put on a USB stick and played in your ENSPIRE.
It’s Time to Play!
At this point, you can move the complete folder (in this case, Kingston Trio) onto a USB stick, and insert it into the front of your ENSPIRE controller.
Once your USB is inserted, you’ll see the My Songs (5) option appear in the ENSPIRE controller app. (This image is copied from the ENSPIRE Controller Operation Manual created by Yamaha, which is available from them.) Just open up the “Album” (which is the folder you created for all of your files on your USB stick), and select a song! It’ll play the piano parts, and the audio will accompany it.
This article on Mark IV Disklavier SSD Conversion was originally contributed by Richard Zajac.
The Mark IV utilized a spinning hard disk, which was more than sufficient for the technology of its time. Even advanced systems like the Yamaha Disklavier don’t demand exceptionally fast read speeds, as piano notes aren’t played within microseconds of each other. However, spinning hard disks do come with inherent drawbacks:
Being mechanical, they are prone to failure, and are noisy. Additionally, during system updates, the limitations of their read and write speeds become evident, resulting in updates that can take nearly an hour to complete.
Whether you’ve chosen to upgrade because of the improved read/write speed, or you’ve simply arrived here because the hard drive has failed, or an update has been interrupted, read on!
First, you’ll need a new solid state drive with a minimum of 80 GB of storage capacity, as well as an IDE to SATA adapter. The 120 GB OWC Mercury Pro Legacy comes with all necessary components. (Note that, although Richard used this, and it fit neatly into the system, I installed mine using a 120 GB Patriot Burst drive and Kingwin SATA to IDE adapter, so my pictures differ. His OWC product is a neat, all-in-one solution.)
Removing the Old HDD
Remove the control unit from the piano by first unscrewing the parallel port connector using the two flat blade nuts on the sides of the port.
Unplug all the cables and then carefully unscrew the control unit from the piano. It is very heavy, so carefully lift it down and turn it over.
Unscrew all the black screws on the top face of the control unit that would normally be against your piano. This surface is the unpainted, silver surface.
Carefully remove the two plugs from the hard drive. Unscrew the drive underneath using a Phillips screwdriver with lots of pressure taking care not to strip the screws.
The original spinning disk, at rest
Imaging the Old HDD
At this point, you’ll need to copy the contents of the old hard drive into an image file.
Make certain you have enough space to store a complete image! The file will be 80 GB total.
Windows
If you’re using Windows, you can use Win32 Disk Imager to take an image of the old disk. I’ve also had people recommend Balena Etcher, although I was unable to get it to work reliably on Windows 10.
Mac
To create your own backup on Linux or Mac, you can use the dd instruction in a terminal. Note that you’ll need to adjust /dev/sdX to be whatever the location of your hard disk is! On Mac, this will be similar to /dev/rdiskX.
You can write IMG files to a disk using Win32 Disk Imager. As mentioned above, I’ve also had people recommend Balena Etcher, but haven’t gotten it to work on Windows 10 myself.
Mac
Using the terminal, type in “diskutil list” command shown as below, then press “Enter” to list all the disks in your Mac computer. Take down the number of your USB drive. Here assume that the USB drive number is “2”.
Type in the following command, replacing “#” with your USB drive number.
diskutil unmountDisk /dev/disk#
Then press “Enter” to unmount it.
Type in the following command. Replace “/path/to/your.img” by dragging the image file from the Finder into terminal.
Then press “Enter” to burn the IMG image file to the USB drive.
Unmount your USB drive, put the red adapter back on, and screw it into your Disklavier top assembly. You will need to use the middle screws to give it enough room to be able to have the cable attached and close it.
Voilà! You have now updated your system and changed your drive to solid state!
My Patriot Burst SSD, mounted directly to the top plate.
I was able to line up the Patriot Burst drive with the cooling holes on the upper plate such that I could screw it directly in place
This Python program will recursively rename .FIL files in the specified directory, ensuring they follow the naming convention described, and convert all filenames to uppercase. If, for instance, you have twenty albums, direct this program to run in their parent directory, and all the albums in subdirectories will be corrected.
This script renames all files to be all-caps including extensions, and for the name to be exactly eight characters long with no symbols. It will add filler characters if necessary. It will make sure they’re unique by incrementing a counter. These appear to be the most important factors in making files identifiable to early Disklaviers, based on my experience and those of commenters.
Usage: python renamefordisk.py [TARGET_DIRECTORY]
Just download renamefordisk.py. The source code is also at the bottom of this page.
As mentioned above, this will either correct all the files in the target directory, or will recursively change the names of all .FIL files in subdirectories if pointed at a parent directory. This is very useful if you’re, for instance, transferring many albums using backing up numerous floppy disks.
At this point, you’re ready to use EEXPLORE.EXE to move through each directory and prepare your PIANODIR.FIL. At a future date, I’d like to automate this.
Make certain to back up all files before running this! I can’t guarantee perfect results for all combinations of names and strings of characters.
Filenames before conversion.
Running ESEQ Explorer on the above directory. The names are deformed using MS-DOS shorthand.
The above is not guaranteed to read in a Disklavier. It is not apparent whether this is because of misbehavior by ESEQ Explorer, or is an issue with older Disklaviers. However, this does make it less likely the tracks will read correctly in older systems.
Filenames after conversion.
ESEQ Explorer with proper disk names. Note that the names are consistent with the names in the directories.
If you see the above, it’s quite likely it’ll read in your older Disklavier.
You can see based on the pictures below that the Nalbantov slim is slightly too small to fill the entire cavity left by the original floppy disk drive. Additionally, there are no mounts of any kind to hold the Nalbantov in place. This insert solves both problems: The drive screws into the insert at just the right distance and depth, and the insert also buffers the area around the outside of the drive.
The insert installed over the screw positions of the original floppy disk drive.I 3D printed the spacers at 50% infill so they’d be fairly solid. These spacers allow you to use the original machine screws that hold down the OEM floppy disk drive, which is a huge advantage. No visits to the hardware store!
I have a customer who recently experienced an issue with his Yamaha Disklavier HQ100. The HQ100 is the Japanese version of the MX100II. He primarily uses this instrument over MIDI, and finds the Disklavier quite useful.
This discussion should apply to other models of Yamaha Disklavier. Although the solenoids and part numbers differ between models, the general concept remains similar.
The symptom was that, when started, the MX100II would play a single key at maximum velocity. It would sustain it for several seconds before releasing. Additionally, the system emitted a noisy whine while powered on. This noise turned out to be a failed power supply, and a replacement resolved that particular symptom. However, despite this, the system would still play one single key after powering on and then fail to respond to any subsequent commands.
The key that was playing was a low D (specifically, D1). I disassembled the instrument and inspected the solenoid for that key. The solenoid assembly was exuding an enormous amount of heat. The burned coil can be seen below.
There was also considerable damage to the inside of the coil assembly. The solenoid was unable to move fully back down into the rest position, as the assembly was badly melted.
A burned out solenoid alongside a healthy one.
Diagnosis
I replaced the solenoid; however, this did not solve the problem. The new solenoid would activate and rapidly heat up. At one point, F1 activated instead of D1, adding an interesting twist.
I disconnected CN201, meaning that the Drive C solenoid drive board was still receiving power from the Disklavier but wasn’t receiving a signal. This isolated the problem to the Drive C board. Replacing the solenoids made it clear that they weren’t the issue. Therefore, the problem had to be somewhere on the PCB below:
I traced the circuitry back from the solenoid. In the image above, the D1 key solenoid is plugged into CN207. I verified that diodes D213-D224 were all behaving correctly (between 400-600 mV forward, and 0 back). Eventually, I was able to trace the behavior to the transistor array. My current theory is that the transistor array failed, causing current to run to the solenoid continuously. The solenoid eventually melted the plastic sleeve. This would also explain why the F1 solenoid activated in place of the D1 during later tests—both key solenoids are attached to the same failing transistor array.
This is the failed component. In the MX100II, this transistor array (2NTH3L20 / Yamaha #VB293700) has been discontinued. However, the equivalent array is NX551020 available through Digikey.
I’ve had a couple of people reach out over the years looking for the bracket that supports the Yamaha DKC-850, otherwise known as the “hanger assembly.” The part number for this is, according to Yamaha, WT79210. Unfortunately, it’s been discontinued. However, you can use the hanger assembly for the Yamaha DKC-800, which is a perfect fit for the DKC-850.
The part number for this hanger assembly is ZE383601, and it’s readily available.
Yamaha’s earlier floppy disks use the propriety ESEQ format. They also use a primitive form of copy protection, where the first sectors of the disks are missing. This means computers identify the disks as corrupt, requiring you to use specialized software to back up your Disklavier disks. In place of these sectors, Yamaha uses the PIANODIR.FIL file, which serves both as a file table and a song index.
PIANODIR.FIL files are not necessary for MIDI files. Do not generate a PIANODIR.FIL for your MIDI files. It will make the disk unreadable to the Disklavier. The PIANODIR.FIL is only for ESEQ (or .FIL) files.
Please also note that, if you’re using the Pianostream, you do NOT need to convert your ESEQ files to MIDI, or do anything with a PIANODIR.FIL. The Pianostream will allow you to play MIDI files to your Disklavier without doing any of this. This article only applies if you’re using floppy disks or floppy disk emulators.
MIDI files that have only one track are called Type 0 files. MIDI files with multiple parts are Type 1. Occasionally, the piano will be spread between two tracks. In that case, you’ll find the piano is playing only half or so of the notes it should be. You can convert Type 1 to Type 0 files using the tool GN MIDI Professional. In addition to converting files individually, the professional version can convert batch groups of files. It has a 14-day free trial, and will either run on Windows or on Linux/Mac using Wine.
Once you download DKVUTILS.ZIP from my site or theirs, you’ll need to extract it. The program that converts MIDI files to ESEQ files is MID2ESEQ.EXE. This program runs only on Windows, and does not seem to run with emulators. Reach out to me and I can assist with conversion.
Using MID2ESEQ, just drag and drop MIDI files into the window.
If you have a Yamaha that’s capable of playing ESEQ only, you might also need to create a PIANODIR.FIL index. Continue scrolling down for instructions!
Creating a PIANODIR.FIL using ESEQ Explorer
If you are creating a floppy disk for use with an earlier ESEQ only Disklavier, or if you’re preparing ESEQ files for transfer to a Nalbantov USB stick, you might have to create your own PIANODIR.FIL.
Note: Please note that the filenames should be strictly eight characters long, have no spaces, and be entirely uppercase, including the FIL extension BEFORE following the process below. If you don’t do this, some pianos will be unable to read the files. I’ve created a program to conveniently rename all your .fil files at once, which is especially helpful if you have numerous albums.
First, put all the ESEQ files you’ve created in a folder together. The DKVUTILS suite includes a program called ESEQ Explorer. Once you open the program, select the directory you’ve stored your ESEQ files in (make sure they’re properly renamed according to the above instructions, or use my program to rename them for you). You’ll see a screen like the one below:
ESEQ Explorer displaying the contents of a Christmas album, with a proper PIANODIR.FIL file already in place.
Note that, if you don’t currently have a PIANODIR.FIL, there will be a red X in front of it. That means it’s not present. Right-click on it and select Create Index. The contents of that folder are now ready to be added to a disk using the Nalbantov tools. If your file names are too long, you’ll see them renamed with ~ symbols. In my experience, this is a program, and indicates they likely won’t read in the piano. Make sure to rename them appropriately first.
I’ve also quoted the text file from the DKVUTILS.ZIP tool below, since they’re informative:
Yamaha Disklavier discs are always on Double Density (2DD) media, High Density (HD)discs, which are more common nowadays, will not work. Furthermore, they are formatted to 720 Kbytes not the default of 1.2 Mbytes. The original discs are copy protected. This has been achieved by placing invalid data on the first sector. As DOS and Windows always refer to this sector to check out a floppy, they will report that the discs are bad. The Yamaha machinery ignores the first sector, so it reads them normally.
The music files on a Disklavier disc have the extension .FIL. They are frequently identified with titles like PIANO001.FIL, but sometimes they have names similar to DOS like MUSIC1.FIL. In addition to the music files, there is an index file on the disc. This contains a list of the active music files on the disc, their titles, and pointers to their position on the disc. The index file is always called PIANODIR.FIL and always has a size of 6 Kbytes. In order to set up a Disklavier disc to function on a Disklavier, you must first copy the music files onto it in Disklavier format (ESEQ) and then run the ESEQ EXPLORER program to build the index file.
Finding More MIDI Files
If you’re having fun converting these files, and you’re looking for more MIDI files to convert for your Yamaha Disklavier, check out my directory of MIDI resources!
My current recommendation is the Kingston 64GB DataTraveler. These are all-metal USB sticks that dissipate heat very nicely, and are durable in the event of an impact. I’ve found them to be both durable and reliable. The 64 GB size is recommended by Nalbantov, as speed with USB sticks correlates with their size, and smaller disks are more likely to cause hiccups with slower speeds.
My previous recommendation: Previously, I recommended the SanDisk Ultra Fit 64 GB. As a smaller USB stick, it was less likely that people would bump into it. I would tie on some Atwood Micro Cord, and tie off the end in a Lanyard (Diamond) Knot. However, I’ve had multiple instances of these drives suddenly corrupting. I’m not sure why this is, but have now moved on from using them. I have many customers who still use them and like them, but can no longer recommend them.
Below, you can see a USB stick the was struck laterally by a pianist. The solder joint snapped right off! That is an in convenience easily avoided by a good quality, low profile USB stick.
Formatting your USB Sticks
When you’re attempting to format 64 GB USB sticks for Nalbantovs, you might run into some trouble on modern versions of Windows. These USB sticks must be formatted FAT32 (not exFAT or NTFS), or else the Nalbantov won’t recognize them. Although these USB sticks come formatted FAT32, you might need to format it if you run into any trouble in the future. In that case, I use the tool fat32format to format these sticks, which is a freeware application. If you’re on Mac or Linux, you should not need any additional software to format them.
A snapped solder joint on an inexpensive USB stick.
I recommend customers with worn-out floppy disk drives upgrade them to “Floppy Disk Emulators.” There are a couple of these on the market. However, the easiest to install and use is the Nalbantov USB Floppy Disk Emulator. I install these regularly in Yamaha Disklaviers, but they can also be installed in keyboards. If you order from Nalbantov directly, make sure to use the AlexPiano for a 5% discount on orders from Nalbantov.
Why Upgrade?
There are several reasons why you might want to replace an old floppy disk drive with a USB floppy disk emulator, including:
Increased reliability: USB floppy disk emulators are more reliable than traditional floppy disk drives. They have no moving parts and are less susceptible to mechanical failure. Most customers reach out to me after their floppy disk drive has failed.
Compatibility & Convenience: USB floppy disk emulators are compatible with modern computers. Most of my customers no longer have floppy disk drives built-in into their computers!
Cost-effectiveness: USB floppy disk emulators are often more cost-effective than purchasing a new floppy disk drive or repairing an old one. Even if you can find a suitable floppy disk drive, compatible drives typically sell for hundreds of dollars! And then you have to purchase floppy disks, which are increasing difficult to obtain.
Operation
After the Nalbantov is installed, you can use a single USB stick to represent up to 1000 floppy disks. Because it’s a floppy disk emulator, the Disklavier actually believes you’re inserting a different floppy disk. As you switch between virtual “disks” by pressing the arrows, you’ll see the display on the Disklavier behave as though you’ve inserted a new disk. Of course, if you have more than 1000 floppy disks, you can invest in another USB stick, although I haven’t run into this particular situation yet!
This is the #2 track on the #27 floppy disk stored on that USB stick!
Installing the Nalbantov
Some customers opt to install the Nalbantov unit themselves. Depending on the design of Disklavier, this is quite doable, although I don’t recommend attempting it with most Yamaha MX100II Disklaviers (see below). It is a very easy installation on, for instance, the DKC5R and the DKC500RW, just to pick a couple of examples.
With some generations of Disklavier (most notably MX100II devices), the floppy disk drives are mounted behind a shaped plastic piece. In these cases, you’ll need to cut away the old plastic facing (a pair of flush-cut nippers is helpful here), install the new drive, and put some kind of buffer around it. I’ve experimented with a few different choices for something functional and attractive. Purchasing neoprene strips is a cheap solution.
New solution: I have a 3D model of a floppy bezel that’s sized to fit around a Nalbantov. You can 3D print this yourself, or I can mail you one. This mount holds the Nalbantov in place, and also fills in the gaps around the edges. It’s an all-in-one solution for mounting the Nalbantov, and allows you to reuse the same screws the original floppy disk drive was installed with.
My customized 3D-printed bezel in place over a Nalbantov.
For backing up your current Disklavier floppy disks to a format that can be stored on your USB stick, see my article on Backing up Disklavier Floppy Disks. They can then be moved onto a virtual “disk” with Nalbantov’s proprietary tool.
This post is intended to help you read from, write to, or replace Yamaha Disklavier floppy disks.
Some of my customers choose to upgrade their older Disklavier’s floppy drive to a Nalbantov USB drive, and want to know how to copy songs from their old Disklavier floppy disks onto a USB. Some of them just want to be able to back up their disks in case they need to make new ones later. Or maybe, you’re just trying to figure out how to write to disks your Disklavier can actually read!
If you’re adding new music to a floppy disk or Nalbantov USB and have an older Disklavier (such as the popular MX100II), you’ll need to make sure the files are in Yamaha’s proprietary ESEQ format. Using the tools below, you can convert your MIDI files to ESEQ so that they will be in your Disklavier’s native language.
The content on the original floppy disk is protected by copyright and is the property of its respective owners. These instructions are provided to assist owners of legitimate copies in converting the files for personal use on their own Yamaha instruments. Unauthorized copying, sharing, distribution, or commercial use of the converted files is strictly prohibited. By using these instructions, you agree to comply with all applicable copyright laws, licensing agreements, and Yamaha’s terms of use. I disclaim any responsibility for misuse of the information provided. Do not ask me for free copies of Yamaha floppy disk images. I will not provide them.
Yamaha floppy disks are a great source of songs that you know will be formatted correctly for your piano. However, floppy disks often don’t age well, and are very susceptible to sunlight and magnetic fields. (This is one more reason to back them up!)
Disklavier floppy disks cannot be natively read by your computer without special software. They will appear as unformatted disks.
There are several tools that will allow you to read them: I use the Player Piano Floppy Backup Utility 1.4, created by Mark Fontana. It’s freeware, but he requests donations. You can download it from him, or you can download ppfbu_v1.4_setup.exe from me. It can read and save directly in ESEQ format, even if the disk it’s reading from is in MIDI. It appears to run acceptably on Mac / Linux using emulators, although this can add complications. When backing up Disklavier floppy disks, there’s no other single tool more useful than PPFBU.
If you copied the files in ESEQ format, there’s an extra step before your Disklavier can read them. See below!
The Player Piano Floppy Backup Utility v1.4 running on my dedicated “floppy copy” box.
Obtaining even More ESEQ Files from the Internet
In addition to the originals you might have, you can sometimes find these on eBay or at local music stores. Older disks on eBay are seldom tested, so there’s some risk of receiving junk disks.
There are several large online repositories in both ESEQ and MIDI formats. Some of these are of dubious legality. One legitimate resource was kuhmann.com, which had quite a large repository. I have a copy of their entire database. (I worry a lot about these older resources disappearing! They disappeared. Kuhmann’s inventory does appear to be available on the Wayback Machine, but his original website is now off the internet.)
You can also source files from Yamaha’s website, although this a more expensive option. Many of their MIDI files have multiple instruments (or even limited piano), and are more designed for their keyboards and other MIDI devices. However, they do have an entire category of Piano Solos, and these are what you’ll want to search for when selecting files. When you download these, you get their associated MIDI files, which are comfortably sized for floppy disk purposes.
Converting MIDI files to ESEQ
If you want to use MIDI files with your older Disklavier, you can, but you have to convert them to ESEQ first. Yamaha Disklavier floppy disks of the era all used this proprietary format, and these Disklaviers cannot read MIDI files natively. However, there’s software that does this conversion for you. You can either get it from http://www.carolrpt.com/MIDItools.htm or you can download the whole DKVUTILS suite from me.
Once you download DKVUTILS.ZIP from my site or theirs, you’ll need to extract it. The program that converts MIDI files to ESEQ files is MID2ESEQ.EXE. This program runs only on Windows, and does not seem to run with emulators. Reach out to me and I can assist with conversion.
Using MID2ESEQ, just drag and drop MIDI files into the window.
MIDI files that have only one track are called Type 0 files. MIDI files with multiple parts are Type 1. Occasionally, the piano will be spread between two tracks. In that case, you’ll find the piano is playing only half or so of the notes it should be. You can convert Type 1 to Type 0 files using the tool GN MIDI Professional. In addition to converting files individually, the professional version can convert batch groups of files. It has a 14-day free trial, and will either run on Windows or on Linux/Mac using Wine.
Using conversion software to merge all the MIDI tracks.
Please also note that the ESEQ filenames should be strictly eight characters long, have no spaces, and be entirely uppercase, including the FIL extension BEFORE creating the PIANODIR.FIL file. I’ve created a script to automate this proper naming process, discussed in my creating a PIANODIR.FIL index instructions.
Formatting 2DD Floppy Disks
Some people choose to use the original floppy disk drives in their 90s-vintage Disklaviers, rather than converting to a Nalbantov. First, it’s important to make certain you’re using the correct floppy disks. The more “modern” 2HD floppy disks require stronger magnetic fields to write, and may not always be compatible with older Disklaviers. The slightly older 2DD drives, however, will work. You can tell the difference readily: 2HD disks have openings at both corners of the Disk, while 2DD disks will have only one.
2HD disks have openings at both corners, but 2DD disks do not. You’ll usually find the write-protect slider in one corner, but the other will be blank.
Some have reported covering the hole with electrical tape will trick the Disklavier into believing the disk is a 2DD disk. You may or may not be able to write to it using the Disklavier, but you should be able to read from it using this trick, provided your 2HD disk is formatted as a 2DD disk.
Formatting a 2DD 720KB floppy disk in Linux.
I formatted mine on my Pop!_OS Linux machine with the instruction sudo ufiformat -f 720 -v /dev/[yourdevice]. If you’re using a Windows machine, the instruction is format a: /t:80 /n:9. Pictured below, you can see what this command looks like on my Windows XP floppy transfer box. This command does work in Windows 10 and 11, but requires you to be using an external floppy disk drive that allows this format. Not all of them do.
Formatting a 720 KB 2DD floppy disk in Windows XP.
At this point, you can transfer your .FIL files and PIANODIR.FIL file to your floppy disk. Put them in the root directory, and do not use any folders.
If you’re using an actual floppy disk, it must be a 2DD disk formatted to 720 KB. See the above section on identifying the disk and formatting it correctly.
You cannot have both ESEQ files and MIDI files on a disk, even if your particular Disklavier can read both file formats. Each disk or virtual disk must use only ESEQ or MIDI.
Earlier Disklaviers can be finicky about their ESEQ files. Sometimes, they’ll work without any trouble, even without a PIANODIR.FIL file. However, particularly in earlier Disklaviers (such as the DK5R), you’ll need to be more careful with the naming conventions, and you’ll definitely need that PIANODIR.FIL described above.
I’m very grateful for the research of Mike Isreal (in the comments below), who did experimentation with his own Disklavier. Beforecreating a PIANODIR.FIL for your disk, make certain that all filenames are precisely eight characters long, and that both the filename and extension are in all-caps. The filename must contain no spaces.
Some have commented that it appears you can also omit the .FIL extension (at least in some cases). According to Nalbantov, there might be cases where a fully lower-case filename and extension are called for, although I have not run into that particular case yet.
