How Donor Drives Are Matched for Head Swaps

A head swap requires transplanting the entire Head Stack Assembly (HSA) from a compatible donor drive into the patient drive (the drive with failed heads). The donor heads must be mechanically compatible with the patient's platters and electronically compatible with the patient's firmware and preamp circuitry. Matching by model number alone is not sufficient. Hard drive manufacturers produce the same model number across multiple hardware revisions, with different head components, preamp chips, and firmware variations within a single model line. Donor matching is a prerequisite for head-swap cases in our hard drive data recovery workflow.

Firmware Revision Matching

The drive's firmware revision is the primary matching criterion. The firmware controls how the drive communicates with the heads: signal timing, read channel calibration, servo decoding parameters, and write current profiles. Heads from a donor with a different firmware revision may not work because the patient drive's firmware expects specific electrical characteristics from the heads that the donor heads do not provide.

Firmware revisions are printed on the drive label. For Seagate drives, this is a four-character code (e.g., CC26, SDM1, 0001). For Western Digital, the firmware revision is part of the extended model number. The firmware revision indicates the generation of controller code and, by extension, the generation of head technology the firmware is calibrated for.

Within a firmware revision, there can be sub-revisions that affect compatibility. Two Grenada drives with firmware "CC26" manufactured six months apart may have different micro-code patches. In most cases, same firmware revision is sufficient. In some Seagate Rosewood drives, even drives with the same firmware revision but from different manufacturing sites (identifiable by the Site Code on the label) have different head compatibility.

Head Map and Head Count

A drive's head map specifies which heads are installed and active. A two-platter drive can have 2, 3, or 4 heads depending on the capacity variant. A Seagate Rosewood ST2000LM007 (2 TB) uses 4 heads across 2 platters. The ST500LM030 (500 GB) uses 2 heads on 1 platter. Both are "Rosewood" drives, but their head assemblies are physically different.

The head map is stored in the drive's firmware and defines which physical head positions are active and how the firmware addresses them. The donor must have the same head map as the patient: same number of heads in the same physical positions. A 3-head donor HSA cannot be used in a 4-head patient drive because the firmware expects to address a head that does not exist, and the physical mounting may differ.

Preamp Chip Compatibility

The preamp is a small IC mounted on the HSA flex cable, inside the sealed drive cavity. It amplifies the microvolt signals from the read heads and drives the write current to the write heads. The preamp model must match between donor and patient because the controller's read channel is calibrated for the specific signal characteristics of that preamp.

Preamp models can be identified by the marking on the chip (visible when the drive is opened) or inferred from the firmware revision and drive family. Common preamp manufacturers include Texas Instruments, Broadcom (Avago), and Renesas. Within the same drive model line, a preamp change usually coincides with a firmware revision change.

Adaptive Parameters and Post-Swap Calibration

Every hard drive generates a unique set of adaptive parameters during factory self-scan. These parameters record the specific calibration data for the drive's individual heads: optimal read channel settings, write current values, fly height compensation, and servo tracking offsets. Adaptive parameters are stored in the drive's System Area on the platters and backed up in the ROM chip on the PCB.

After a head swap, the patient drive's adaptive parameters no longer match the installed heads. The parameters were calibrated for the original heads, not the donor heads. In some cases, the drive can still read with minor degradation. In other cases, the mismatch prevents the drive from reading its own System Area, causing it to fail initialization.

PC-3000 can modify adaptive parameters after a head swap. The technician can load the donor drive's adaptive parameters into the patient drive's firmware, aligning the calibration with the installed heads. This is not always necessary (some drive families tolerate mismatched adaptives well enough for imaging), but it improves read stability and reduces errors on drives where the mismatch causes issues.

Manufacturing Date and Factory Site

The closer the donor is to the patient in manufacturing date and production site, the higher the compatibility probability. Drives manufactured in the same batch at the same factory use the same component lots: same head wafer, same preamp batch, same platter lot. Component-level consistency within a production batch is high.

Western Digital encodes manufacturing information in the DCM (Drive Configuration Matrix) printed on the label. The 5th and 6th characters of the DCM indicate the head stack supplier and preamp configuration. Two drives with the same model number and firmware revision but different DCM codes may have incompatible heads.

Seagate uses a combination of the Part Number (PN), Site Code, and Date of Manufacture printed on the label. The Site Code identifies the factory (e.g., WU for Wuxi, SU for Suzhou, TK for Thailand). Two Seagate drives with matching model numbers and firmware revisions but different Site Codes or Part Numbers may have incompatible head assemblies.

How Labs Maintain Donor Inventory

Professional recovery labs maintain an inventory of donor drives organized by manufacturer, model family, firmware revision, head map, and manufacturing date range. Common drive families that fail frequently (Seagate Rosewood, WD Blue/Green 2.5", Samsung Spinpoint M8) are stocked in higher quantities.

When a patient drive arrives, the technician identifies the required donor specifications from the drive label and firmware. If the lab has a matching donor in stock, the head swap can proceed immediately. If not, the lab sources one from supplier networks, which may take 1-5 days depending on the drive's rarity.

Donor drives are purchased specifically as parts inventory. They are functional drives that have been verified to read and write normally. Using a donor from a failed drive (e.g., a drive that had bad sectors but working heads) is possible but risky: the heads may be degraded even if they currently function.

Firmware Family Architecture by Manufacturer

Hard drive manufacturers iterate on base firmware architectures across multiple product generations. Recognizing which firmware family a drive belongs to is the first step in donor matching, because cross-family donors are incompatible even when the model number prefix looks similar. Each family uses a distinct read channel configuration, SA module layout, & head addressing scheme.

Seagate F3 Architecture (Grenada, Rosewood, Makara)

Seagate's F3 architecture covers drives where the firmware revision is a short alphanumeric code without a period (e.g., CC49, SBK2, SDM1). Within F3, three sub-families have distinct matching requirements:

Grenada (7200.14 desktop)

Desktop 3.5" drives including the Barracuda ST1000DM003 & ST2000DM001. Grenada matching depends on firmware revision, head map, & preamp chip. The preamp revision is visible on the HSA flex cable when the drive is opened. Certain preamp substitutions are possible within the same generation (e.g., a B2 preamp can sometimes substitute for a CA in the same firmware revision), but cross-generation swaps fail.

Rosewood (2.5" mobile)

The Rosewood family includes the ST1000LM035, ST2000LM007, ST1000LM048, & ST500LM030. These are among the most common drives in recovery labs. Rosewood matching is complicated because the preamp revision is not printed on the drive label, and the serial terminal is locked on most units. The preamp must be identified by opening the drive or estimated from the Date of Manufacture. Two common Rosewood preamp revisions (C202 & 8202) are not interchangeable; a donor with C202 heads will not produce stable reads in a patient that originally used 8202, even with identical firmware.

Makara (enterprise & high-capacity)

Shares structural DNA with Grenada but uses different head map logic & servo calibration optimized for sustained sequential workloads. Makara donors are not interchangeable with Grenada despite similar firmware revision formats. The SA module layout differs, and the adaptive parameter tables use different calibration ranges.

Western Digital Marvell-Based Architecture

Western Digital transitioned from older Caviar IDE/SATA controllers to Marvell-based MCU architectures. Modern WD drives are categorized into Marvell Version 1 & Version 2, distinguished by the family code in the model number.

WD donor matching requires aligning three parameters: the full model number, the physical head map, & specific characters within the DCM (Drive Configuration Matrix). The 5th character of the DCM encodes the head stack supplier. Two drives with identical model numbers & firmware but different 5th DCM characters have physically different head assemblies from different component vendors.

WD firmware stores the head map in ROM Module 0A. Module 30 contains the SA translator (initial preamp calibration values & compiler data), and Module 47 holds the SA Adaptives (servo parameters & head-specific calibration). For modern Shingled Magnetic Recording (SMR) drives such as the WD10SPZX & WD20SPZX, Module 190 contains SMR-specific operational data. A donor for an SMR drive must have compatible Module 190 data, adding an additional matching constraint that CMR drives do not require.

Toshiba MQ & MK Series

Toshiba drives have the most forgiving donor matching requirements among the three major manufacturers. For the older MK series (MK6475GSX), matching the full model number & PCB family number is typically sufficient. For the modern MQ series (MQ01ABD, MQ04ABF), matching the full model number & the HDD Code printed on the label covers most compatibility cases.

One edge case: drives manufactured in different countries (China vs. Philippines) occasionally differ in read channel calibration. If a model-matched donor produces unstable reads, the next donor should match both the model number & country of manufacture.

SA Adaptives & Microjog Calibration

Service Area (SA) adaptive parameters are head-specific calibration values generated during factory testing. After a head swap, these parameters no longer match the installed donor heads. PC-3000 can transfer the donor's adaptives into the patient drive's firmware to restore read stability, but the process varies by manufacturer & firmware family.

On Western Digital Marvell-based drives, SA Adaptives are stored in Module 47. This module contains voltage settings, read channel gain profiles, & servo calibration values specific to each head position. If the donor heads deviate from the patient's Module 47 values, the drive may fail to read its own Service Area on power-up, resulting in a clicking loop or immediate head park. The technician uses PC-3000 to replace the patient's Module 47 with the donor's version, allowing the firmware to calibrate for the installed heads.

Microjog values are a subset of the adaptive data. During factory calibration, the drive measures microscopic alignment offsets for each head on the actuator arm & records compensation values. These values correct for physical variation in head placement that is unavoidable during HSA manufacturing. When a donor HSA has microjog values close to the patient's original values, the swap is more likely to produce stable reads without additional intervention. Large deviations in microjog values indicate the donor heads are physically misaligned relative to what the patient firmware expects, which causes read errors & sector instability during imaging.

Seagate F3 drives handle adaptives differently. The adaptive tables are embedded in the SA modules on the platter surface, and the ROM chip on the PCB contains a backup. PC-3000's Seagate F3 utility can read, edit, & write these modules. For Rosewood drives, the technician may need to use a hot-swap technique (powering on with the donor HSA, then physically swapping to the patient platters while the controller remains initialized) to bypass the locked terminal.

PC-3000 Head Testing Workflow

After installing a donor HSA, the technician uses PC-3000 to evaluate whether the donor heads can read the patient drive's data. This is a structured diagnostic sequence, not a single pass/fail test. The workflow determines head compatibility, identifies weak heads, & guides the imaging strategy.

1. SA Module Read Test. Power on the patient drive with the donor HSA installed. PC-3000 attempts to read the Service Area modules (the firmware stored on reserved platter tracks). If the drive reads its SA successfully, the donor heads are electrically compatible with the patient's controller & preamp circuit. If the SA read fails, the heads are incompatible or the adaptives need transfer.
2. Head Stability Evaluation. PC-3000 reads sample sectors from each head position & reports the error rate per head. Donor heads are never perfectly calibrated for the patient's platters; some read degradation is expected. The technician evaluates whether each head reads well enough for sustained imaging or if specific heads need to be disabled in the head map to prevent platter damage from a weak head dragging.
3. Conditional Adaptive Transfer. If the SA read succeeded but the error rate is high, the technician transfers the donor's adaptive parameters into the patient firmware. On WD drives, this means replacing Module 47. On Seagate F3 drives, this means editing the SA adaptive tables. The drive is then power-cycled & the head stability test is repeated.
4. Selective Head Map Configuration. If one or more heads are unstable after adaptive transfer, PC-3000 can disable specific heads in the firmware head map. The imaging proceeds using only the stable heads, recovering data from the platter surfaces those heads can reach. Data on surfaces served by the disabled heads may require a second donor attempt with a better-matched HSA.

Drive Family Matching Pitfalls

Each drive family has specific compatibility traps that general matching rules do not cover. These pitfalls come from undocumented component changes, manufacturing site differences, & firmware sub-revisions that are not reflected on the drive label. The following notes apply to the drive families most commonly seen in recovery labs.

Seagate Rosewood Pitfalls

The Rosewood 2.5" family (ST1000LM035, ST2000LM007, ST1000LM048) accounts for a large share of consumer head-swap cases. The primary matching hazard is the preamp revision. Two preamp generations (C202 & 8202) are in circulation, & neither is printed on the label. Drives manufactured before approximately mid-2017 tend to use C202; drives manufactured from 2018 onward tend to use 8202. The Date of Manufacture printed on the label provides the best external estimate.

A secondary clue is the serial number. Drives with matching 2nd & 3rd serial number characters are more likely to share internal components, though this correlation is not absolute. The only definitive verification is opening the drive & reading the preamp marking on the HSA flex cable, or reading the preamp identifier through PC-3000 after a successful SA initialization.

WD Blue & Green (Marvell Platform)

Modern WD 2.5" drives (WD10SPZX, WD20SPZX, WD10SPCX) use the Marvell controller platform. The DCM is the critical external matching reference. The 5th character identifies the head stack supplier; donors with a different 5th character will have a physically different HSA even when the model number & firmware match.

For SMR variants, the translator layer that maps logical blocks to overlapping physical tracks adds a firmware-level matching requirement. Module 190 in the ROM contains the SMR operational parameters. A donor from a CMR variant of the same model line will not have valid Module 190 data, and the firmware will fail to initialize the translator after the head swap.

Toshiba MQ Series

Toshiba MQ drives (MQ01ABD050, MQ01ABD100, MQ04ABF100) are the most forgiving for donor matching. Matching the full model number is sufficient in most cases. The HDD Code printed on the label serves as a secondary criterion if the first donor produces unstable reads.

The one consistent pitfall is country of manufacture. Toshiba drives from Chinese factories & Philippine factories occasionally differ in read channel calibration. If a model-matched donor fails, the technician tries a donor from the same country of manufacture before escalating to other diagnostic steps.

Samsung / Seagate Momentus Hybrid Drives

After Seagate acquired Samsung's HDD division, several drive models carry Seagate branding but use Samsung-designed internals. The ST1000LM024 is a Samsung Spinpoint M8 with a Seagate label. Donor matching for these drives must follow Samsung logic (full model number & PCB part number), not Seagate F3 logic. Using a Seagate F3 donor for a Seagate-branded Samsung drive will fail because the SA module layout, head addressing, & preamp circuitry are Samsung architecture. PC-3000's Samsung utility (not the Seagate F3 utility) is required for SA access & adaptive parameter management on these drives.

Head swap on Samsung/Seagate hybrid drives follows standard head swap pricing at $1,200–$1,500. Donor drives are matching drives used for parts. Typical donor cost: $50–$150 for common drives, $200–$400 for rare or high-capacity models. We source the cheapest compatible donor available.

Frequently Asked Questions