iMac HDD → SSD Upgrade (Bench Procedure)

Section: Apple Hardware Tags: imac, ssd, hdd, upgrade, storage, performance, crucial, bench-work Source tickets: #26566, #22925 Confidence: High — standard bench procedure used across multiple client iMacs

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Overview

Older iMacs (2011–2019) shipped with spinning HDDs that are now severely performance-limited with modern macOS. Replacing the HDD with an SSD is the single most impactful upgrade possible — typically transforming a sluggish machine into one that feels near-new. This article covers the parts, data migration, and installation procedure. Typical cost (parts only, 2024 pricing): £80–£130 depending on SSD capacity.

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When to Recommend

• iMac is very slow to boot (>60 seconds to desktop)
• Apps take >10 seconds to launch
• Apple Diagnostics or SMART status shows HDD warnings (diskutil info /dev/disk0 → look for "SMART Status: Failing" or "Verified")
• Client complains of general sluggishness on a machine that is otherwise in good physical condition
• HDD is confirmed spinning (not SSD): About This Mac → System Report → Storage — SSD shows "Solid State: Yes"

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Parts Required

Order before the machine arrives. Standard Purple Computing spec: ItemSpecExample --------------------- SSDCrucial MX500, 500GB or 1TBuk.crucial.com/ssd/mx500-ssd USB EnclosureIcy Box IB-254U3 (for cloning and post-install data access)Amazon Thermal Sensor (iMac 2011–2012 only)OWC Digital Thermal Sensor — match to year/modelowcdigital.com Note: iMac models 2011–2012 have a proprietary Apple thermal sensor on the HDD cable. Without the OWC replacement sensor, the iMac's fans will run at maximum speed after the swap. From 2013 onwards, no sensor adapter is needed.

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Procedure

Phase 1 — Data backup (before machine leaves client)

• Check Time Machine: confirm last backup is recent (<24 hours)
• If Time Machine is not configured or backup is stale: connect an external drive and run CCC (Carbon Copy Cloner) to create a bootable clone before collection
• Confirm backup status in the ticket notes

Phase 2 — Clone HDD to new SSD (at bench)

• Fit the new SSD into the USB enclosure
• Connect enclosure to the iMac
• Open Disk Utility → format the SSD as APFS (for macOS 10.13+) or Mac OS Extended (Journaled) for older
• Launch Carbon Copy Cloner → Source: internal HDD, Destination: new SSD in enclosure
• Click Clone — allow 1–3 hours depending on data volume
• After clone, boot from the SSD: hold Option at startup → select the USB-connected SSD
• Confirm macOS boots correctly and all data is present before opening the machine

Phase 3 — Physical installation

> ⚠️ Destructive step — this requires removing the iMac screen. If in doubt, consult iFixit guide for the specific model year before proceeding.

• Power off and unplug the iMac
• Use iFixit kit to remove the adhesive strips and carefully lift the glass/LCD panel
• Disconnect the HDD SATA, power, and thermal sensor cables
• Remove HDD mounting screws (typically Torx T6 or T8)
• Seat the new SSD — connect all cables in reverse order (thermal sensor cable first on 2011–2012 models)
• Carefully refit the screen — use new adhesive strips if the originals are no longer tacky
• Power on and confirm boot

Risk: Destructive — screen removal carries a risk of cracking the LCD if the adhesive has hardened significantly (common on older machines). Always advise client of this risk before proceeding. An iFixit heat gun softens the adhesive safely.

Phase 4 — Post-installation

• Boot from the internal SSD (should now be the default)
• Open About This Mac → Storage — confirm SSD is showing as the startup disk
• Run Disk Utility → First Aid on the new volume
• Open System Preferences → Time Machine — re-select the backup disk (the old TM backup history is compatible)
• Run a Time Machine backup and confirm it completes

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Verification

Boot time should be under 20 seconds. App launch times (Outlook, Chrome) should be 1–3 seconds. Run the machine for 30 minutes and confirm no instability. Run Apple Diagnostics (hold D at boot) — should pass with no errors.

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If This Fails

• Fans at full speed after install: Thermal sensor not connected correctly (2011–2012 iMac) — reopen and check the sensor cable seating. If the OWC sensor adapter was not ordered, order it before returning the machine.
• Machine won't boot from new SSD: Startup disk not set — hold Option at boot, select the SSD, then in System Preferences → Startup Disk, set it permanently.
• Clone boot fails (APFS volume error): Re-clone using CCC's APFS-to-APFS option; or restore from Time Machine instead of cloning.

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Related

• Article: macOS Machine Crashing / Hanging — for pre-upgrade diagnosis
• Article: Time Machine Backup Failures to Synology NAS — if backup is failing pre-upgrade