Alignment disk?
Peter Sterrantino
Patrick Linstruth
Here is a list of known 8-inch floppy disk alignment disks (also called Analog Alignment Diskettes or AADs). These specialized media were primarily produced by Dysan (the most common brand) and occasionally by drive manufacturers or other companies like Accurite. They contain precision-recorded patterns (e.g., "cat's eye" bursts) for oscilloscope-based calibration of head radial alignment, azimuth, index timing, track 0 sensor, and related parameters on vintage 8-inch drives (typically 48 TPI, single- or double-density, single- or double-sided).
Dysan 8-Inch Alignment Disks
- Dysan 360/2A (also referred to as 360-A or 360 2A): The most widely documented and commonly used model. Designed for general-purpose alignment of 8-inch drives, including Shugart SA800/SA850 series and many compatibles. Supports single- and double-sided drives (the /2A indicates double-sided capability). Includes patterns for radial alignment, azimuth, and index. Often comes with a detailed instruction manual.
- Dysan 500: Specifically for Pertec flexible disk drives (e.g., FD400, FD500, FD510, FD511 series). Physically compatible with standard IBM 8-inch media but recorded with special signals for Pertec-specific adjustments like radial head alignment on track 38, index/sector photo-transistor alignment, and track-zero switch. Caution: Do not write to it, as it can destroy the alignment data.
Other 8-Inch Variants and Manufacturer-Specific Disks
- Qume DataTrak 8 alignment disk (Qume P/N 50152-02): Used with Qume DataTrak 8 drives for head actuator alignment and related adjustments.
- CDC (Control Data Corporation) alignment disks: Mentioned in retro communities alongside Dysan models; specific part numbers vary but often compatible with CDC 8-inch drives (e.g., patterns on tracks like 00, 37, 75 for certain models).
- Drive-specific or OEM versions: Some manufacturers (e.g., Shugart, Mitsubishi, Tandon, NEC) recommended or supplied their own CE (Certified Engineering) disks, which were sometimes rebranded Dysan media or custom recordings. Examples include disks for Shugart SA800/850 or half-height models like SA860. Exact numbers are often listed in individual drive service manuals
Peter Sterrantino
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On Apr 18, 2026, at 8:34 AM, Peter Sterrantino <sterra...@gmail.com> wrote:I’m heading down to VCF East and was wondering if I see an “alignment disk”, what am I looking for? Are these generic? Or are they specific to a particular drive? And what do you all think is a good price for one?Pete
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Walt Perko
What alignment disks are there for 8 inch floppy drives?
Alignment disks for 8-inch floppy drives were made by a few key manufacturers, and they’re typically categorized by what aspect of the drive they help align (radial, azimuth, speed, etc.). Here are the main ones you’ll run into:
🔧 Major Alignment Disk Types (8-inch)
1. Radial (Track Alignment) Disks
- Used to align the head to the center of tracks.
- Typically include precision-recorded reference tracks (often Track 0, 40, or 77).
- Require an oscilloscope to peak the signal.
Common examples:
- Dysan 224 Alignment Diskette
- Verbatim Alignment Diskette
- 3M Alignment Disk
2. Azimuth Alignment Disks
- Used to adjust the angular alignment of the read/write head.
- Ensures maximum signal amplitude and proper high-frequency response.
Often combined with radial disks in a multi-purpose alignment disk.
3. Speed (RPM) / Strobe Disks
- Used to verify spindle speed (typically 360 RPM for 8” drives).
- Viewed under a fluorescent light or with a strobe.
Examples:
- Dysan Speed Alignment Disk
- Shugart SA800 Speed Disk
4. Index Timing Disks
- Used to verify index hole timing relative to recorded data.
- Important for proper sector timing in some controllers.
5. Write/Read Certification Disks
- Used to test overall drive performance (error rates, signal quality).
- Often paired with diagnostic software.
🧰 Manufacturer-Specific Alignment Packs
Some drive manufacturers shipped their own official kits:
- Shugart
Associates
- SA800/801 alignment diskettes and procedures
- IBM
- IBM 3740-compatible alignment disks (hard-sector formats too)
- Memorex
- CDC
⚠️ Reality Check (Important)
- Genuine alignment disks are rare and expensive now — often hundreds of dollars.
- They degrade over time (oxide shedding, demagnetization).
- Many on the market are not trustworthy anymore unless verified.
🧠 Practical Modern Alternatives
Since you’re working with S-100 / Altair-class hardware, people today often:
- Use a known-good reference drive instead of an alignment disk
- Use software-based alignment tools (CP/M diagnostics, signal peak methods)
- Use a scope + test disk you trust (less precise but workable)
💡 Pro Tip (from vintage hardware practice)
For Shugart-compatible drives like the SA800:
- Align Track 0 using the mechanical stop
- Then peak signal on Track 40 or 77
- Use a scope on the read data line — not just “does it read”
If you want, I can:
- Recommend a specific alignment procedure for your exact drive (SA800, Persci, etc.)
- Or show how to fake an alignment disk using another calibrated drive (a trick many Altair restorers use)
Show how to fake an alignment disk using another calibrated drive
You can “fake” an alignment disk pretty effectively using a known-good, already-aligned drive as your reference. This is actually how a lot of S-100/Altair restorers keep systems running without risking rare factory disks.
Here’s the practical, no-nonsense method.
🧰 What You Need
- A reference drive (properly aligned, or at least reads known-good disks reliably)
- Your target drive (the one you want to align)
- A blank or expendable 8” disk
- An oscilloscope (strongly recommended)
- A system that can step tracks (Altair, CP/M box, etc.)
If your reference drive is off, everything you do will inherit that error—so pick your best drive.
🧪 Step 1: Create a “Reference Disk”
Use the good drive to write clean, consistent data.
Method A (Best – uniform pattern)
Write the same repeating byte pattern across the entire disk:
- 00h, FFh, or E5h (CP/M default fill)
- This creates a stable, repetitive flux pattern
Under CP/M, you can:
- Format a disk
- Fill it with a single file containing repeated data
Method B (Better – track-specific reference)
If you have low-level tools:
- Write
known data specifically to:
- Track 0
- Track 40 (midpoint)
- Track 77 (outer track)
These are the tracks you’ll use for alignment peaking.
📏 Step 2: Use It Like an Alignment Disk
Now move that disk to the misaligned drive.
🔧 Radial Alignment (most important)
- Step to a reference track (usually Track 40 or 77)
- Hook
your scope to:
- Read Data line (or test point on the analog board)
- Adjust
the stepper position (or rails, depending on drive):
- You’re looking for maximum signal amplitude
- Peak the waveform cleanly and symmetrically
👉 You’re not just looking for “it reads”—you want the strongest, cleanest analog signal
🎯 Fine Trick (critical insight)
Once you find the peak:
- Move slightly inward → note signal drop
- Move slightly outward → note signal drop
👉 True alignment is the center of that peak, not just the highest spike
🧭 Track 0 sanity check
- After aligning mid-track, go back to Track 0
- Ensure:
- It still reads reliably
- The head hits the stop correctly
If not:
- You may need to tweak the Track 0 stop separately
🔄 Cross-check
If possible:
- Write a disk on the aligned drive
- Read it on the reference drive
👉 If both drives agree, you’re aligned well enough for real use
⚙️ Azimuth Alignment (optional but valuable)
If your drive allows head rotation:
- Stay on a reference track (40 or 77)
- Adjust head angle slightly
- Watch high-frequency content on the scope
👉 You want:
- Maximum amplitude
- Cleanest waveform (least smearing)
⚠️ Limitations (be honest about it)
This method:
- ✅ Works very well for real-world interoperability
- ❌ Is not lab-grade calibration
- ❌ Won’t match factory alignment disk precision
But for:
- Shugart SA800
- Persci 277
- MPI 88-D
…it’s absolutely good enough to get reliable reads/writes across systems.
💡 Advanced Trick (used by restorers)
If you have two decent drives but neither is trusted:
- Align Drive A to Drive B
- Align Drive B to Drive A
- Iterate until both converge
👉 Surprisingly effective—errors average out instead of compounding
🧠 Bottom Line
You’re not really “faking” an alignment disk—you’re:
Using one drive as the calibration standard for another
That’s exactly how many shops did it in the field when factory disks weren’t available.
.
Peter Sterrantino
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Peter Sterrantino
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On Apr 18, 2026, at 8:34 AM, Peter Sterrantino <sterra...@gmail.com> wrote:
I’m heading down to VCF East and was wondering if I see an “alignment disk”, what am I looking for? Are these generic? Or are they specific to a particular drive? And what do you all think is a good price for one?Pete
--
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Joseph Corda
hoping next year I will have a chance to attend.
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