Our take
Seagate's Expansion Portable 640GB is worth considering when 640GB is enough and a documented USB 2.0 connection fits the host. Seagate identifies model ST906404EXA101-RK as a 640GB Expansion Portable hard drive, and B&H's exact-model page lists USB 2.0 and 5400 rpm. Those records establish a specific legacy configuration; they do not establish current computer compatibility, the power arrangement, or a current Amazon offer.
A buyer with a USB 2.0 host who needs at least 400GB, can leave power requirements open, and will confirm the seller's model and unit condition.
Buyers who require USB 3.0, confirmed operation without an external adapter, at least 1TB, current software support, or a verified current Amazon product listing should choose a configuration with those details documented.
Pros & cons
What could work for you, and what to consider before buying.
What works in its favor
- The model code and 640GB capacity match on Seagate's support catalog and B&H's exact-model record.
- The B&H page documents USB 2.0 for a buyer with that host requirement.
- Its listed 5400 rpm speed is a concrete hardware specification, not an unverified performance claim.
What to weigh up
- 640GB is below the 1TB options in this comparison.
- USB 2.0 does not meet a USB 3.0 interface requirement.
- The saved sources leave power, cable contents, current compatibility, current offer identity, and any individual unit's condition unresolved.
The key details
| Model covered | ST906404EXA101-RK |
|---|---|
| Advertised capacity | 640GB nominal |
| Drive configuration | Portable HDD; 5400 rpm listed |
| Host connection | USB 2.0 |
Performance figures are manufacturer claims. Source checked October 10, 2026. Regional models and included accessories can differ.
What the features mean for you
Does the model number identify this exact 640GB drive?
The Seagate support catalog names ST906404EXA101-RK as an Expansion Portable 640GB hard drive. B&H independently gives the same manufacturer part number for its 640GB listing. This is enough to retain the verified model identity in the saved roster. It does not prove that the historical source-row ASIN B0027IS4KQ still resolves to this configuration or that any present seller has the same item. When shopping, compare the printed model number on the seller's offer and on the unit label. The catalog also links manuals and a data sheet, but the saved evidence does not establish current support for a particular computer or operating system.
Is 640GB enough for the files you plan to keep?
Treat 640GB as advertised capacity, not a promise of the full amount being available for files after formatting. It may suit a bounded backup or transfer set if you already know its size. It gives less nominal room than the 1TB and larger drives in this comparison, so a growing photo, video, or system-image collection may outgrow it sooner. The sources do not provide a workload-based recommendation or usable-capacity measurement. If your minimum is 1TB, this model does not meet it; if a documented 400GB floor is enough, its stated capacity clears that threshold.
What does its USB 2.0 connection change?
B&H lists USB 2.0 for this exact model. That can make the interface relevant to a host that requires a documented USB 2.0 drive, while it does not meet a USB 3.0 requirement. The comparison includes the 640GB Transcend StoreJet 25M3 with a documented USB 3.0 connection, so buyers with the same capacity need can distinguish them by interface. This is a compatibility distinction, not a claim about measured transfer time on a particular computer. A USB 2.0 label and a listed 5400 rpm spindle speed do not predict the throughput of an old drive, cable, host controller, or workload.
Can you count on USB power or an included cable?
No such claim is supported by the saved exact-model sources. Portable describes the product line, but it does not establish whether this drive runs from the host port alone or whether an external adapter is needed. The B&H page does not provide a current package inventory, and an old listing cannot verify what a present seller will include. If you need a no-outlet setup, ask for the exact power requirement and confirm that the offered cable is present. Until that is documented, a strict bus-power filter should leave this model out rather than assume it qualifies.
What should you verify before buying an old or used unit?
The B&H page says its own listing is no longer available; that is not a statement about every seller. Neither source proves a live Amazon offer, today's price or stock, warranty eligibility, current operating-system support, included accessories, or the health of a particular drive. The historical ASIN is not a current product mapping. Use the tagged exact-model search only to find possible offers, then verify the code, capacity, interface, power needs, cable, return terms, and seller's description. For any used unit, test it and keep another copy of important data; the model specification cannot establish the health of an individual disk.
Who should shortlist this model?
Choose this Seagate when you need at least 400GB but less than 1TB is adequate, USB 2.0 is the connection you need, and the seller can answer the unanswered power and condition questions. Choose the same-capacity Transcend when a USB 3.0 connection is an essential documented requirement. Choose a larger product when the archive needs 1TB or more, and choose a product with documented bus power when you must work away from an outlet. No price, performance test, buyer review, or current offer comparison in the saved sources supports ranking this drive as faster, cheaper, or better value.
What else to compare
Before you buy
What is the exact model?
Seagate's catalog and B&H's listing identify ST906404EXA101-RK as an Expansion Portable 640GB hard drive.
Is it USB 3.0?
B&H lists USB 2.0 for this exact model; the saved evidence does not document a USB 3.0 interface.
Is it bus-powered?
The saved exact-model sources do not establish its power arrangement. Confirm it with the seller before relying on a no-adapter setup.
Is B0027IS4KQ a current Amazon product link?
No. It is the historical source-row ASIN. The affiliate destination is an exact-model search link that carries buyershortlists-20.
Where can I check the current price?
Use the Amazon link for current offers. Check the exact model, seller, product condition, delivery, and return terms. This page does not display a live price or confirm stock.
Sources & review basis
We use the following manufacturer documentation for the product features above. Our suitability notes and buying advice are editorial judgments based on those features, not measured performance results.
- Seagate Expansion Portable support catalog and B&H exact-model listing, reopened 2026-10-10 ↗ — checked October 10, 2026.
- Seagate Expansion Portable support catalog; lines 412–423 identify ST906404EXA101-RK and 640GB ↗ — checked October 10, 2026.
- B&H exact-model listing; lines 42–61 identify model, capacity, USB 2.0, 5400 rpm, and the seller's no-longer-available status ↗ — checked October 10, 2026.
The decision
Seagate's Expansion Portable 640GB is worth considering when 640GB is enough and a documented USB 2.0 connection fits the host. Seagate identifies model ST906404EXA101-RK as a 640GB Expansion Portable hard drive, and B&H's exact-model page lists USB 2.0 and 5400 rpm. Those records establish a specific legacy configuration; they do not establish current computer compatibility, the power arrangement, or a current Amazon offer.
Is it the right fit?
Check the exact model and today’s offers on Amazon.