Storage is the component where the marketing numbers correlate least with the experience. A drive advertising 7,000 MB/s alongside one advertising 3,500 MB/s suggests one is twice as fast. In everyday use — booting, launching applications, loading games — the difference is frequently imperceptible, while the difference between either of them and a mechanical hard drive is the single most noticeable upgrade available to an older machine.
Understanding why requires knowing which measurement actually governs how a drive feels.
Sequential versus random
The large figure on the box is sequential throughput: the rate at which a drive reads or writes one large contiguous file. It is the easiest number to maximise and the least relevant to normal use.
Almost everything a computer does with storage is random access: reading thousands of small, scattered files. Booting an operating system, launching an application, loading a game level — all of these are dominated by how quickly a drive can service many small requests, not by how fast it can stream one large one.
Random performance differs far less between SSDs than sequential performance does. Two drives an order of magnitude apart on the box can be within a few percent of each other on the operations that determine responsiveness. This is why a top-tier NVMe drive feels almost identical to a mid-range one in normal use, while both feel dramatically different from a hard drive — where random access requires physically moving a head across a spinning platter, and the gap is measured in orders of magnitude rather than percentages.
The practical rule: sequential speed matters if you routinely move very large files — video projects, large archives, disk images. For everything else, it is close to irrelevant.
The three tiers
| Hard drive | SATA SSD | NVMe SSD | |
|---|---|---|---|
| Sequential read | 80–160 MB/s | ~550 MB/s | 3,000–14,000 MB/s |
| Random access | Very slow | Fast | Fast |
| Interface limit | SATA | SATA (~550 MB/s ceiling) | PCIe |
| Cost per gigabyte | Lowest | Low | Moderate |
| Moving parts | Yes | No | No |
| Best use | Bulk archive storage | System drive on older boards | System drive; everything |
The SATA ceiling is worth understanding: around 550 MB/s is a limit of the interface, not of the drive. Every SATA SSD reaches roughly the same sequential figure regardless of price, because they are all saturating the same connection. NVMe drives bypass this by connecting over PCIe directly.
PCIe generations
NVMe drives are sold as Gen3, Gen4 or Gen5, referring to the PCIe generation they use. Each generation roughly doubles available bandwidth.
The bandwidth is real, and for most people it changes nothing. Gen4 and Gen5 drives deliver sequential figures far beyond what any consumer workload requests, and because random performance does not scale with the interface, everyday responsiveness is largely unaffected. A Gen5 drive boots Windows at essentially the same speed as a good Gen3 drive.
Two practical notes. Drives are backward compatible — a Gen4 drive works in a Gen3 slot at Gen3 speeds, so a faster drive is never wasted, merely constrained. And the fastest drives generate meaningful heat and often require a heatsink; many motherboards supply one, and a drive throttling from heat is slower than a cooler drive one generation behind.
DRAM cache: the specification that matters and is rarely listed
This distinction separates drives that stay fast from drives that do not, and it is frequently absent from retail listings.
An SSD maintains a mapping table between logical addresses and physical flash locations. Drives with a dedicated DRAM cache hold this table in fast memory on the drive. DRAM-less drives borrow a portion of system memory instead, or store the table in flash.
On light workloads the difference is small. Under sustained load — copying large amounts of data, working with many files at once, or when the drive is nearly full — DRAM-less drives degrade noticeably, sometimes dropping below SATA speeds despite being NVMe. If a listing does not mention DRAM, the drive most likely does not have it.
For a system drive, prefer a drive with DRAM. For secondary bulk storage that is mostly read rather than written, a DRAM-less drive is a reasonable economy.
SLC caching and why write speeds collapse
This explains a phenomenon that looks like a defect and is not.
Consumer SSDs store multiple bits per flash cell, which is what makes them affordable, but writing in that mode is slow. To hide this, drives reserve a portion of their flash and operate it in a faster single-bit mode as a write buffer. Incoming writes land in this fast cache and are migrated to slower storage afterwards.
The cache is finite. Write enough data in one go and it fills, after which write speed drops to the drive's native rate — sometimes by a factor of five or more. A drive advertising 5,000 MB/s might sustain 800 MB/s once the cache is exhausted. This is normal behaviour, not a fault, and it is why transferring a very large file often starts fast and then slows abruptly.
Two things follow. Cache size usually scales with drive capacity, so larger drives sustain high write speeds for longer. And keeping a drive well below full matters — a nearly full drive has less space to allocate as cache, which is part of why drives slow down as they fill.
How much capacity
- 256 GB: too small for a modern system drive. The operating system plus a few applications will consume most of it, and the resulting near-full state degrades performance.
- 500 GB: a workable minimum. Adequate for the system and a modest selection of games.
- 1 TB: the sensible default for most builds. Enough for the system and a real games library without constant management.
- 2 TB and above: worthwhile for large game libraries, video work, or anyone who dislikes deciding what to uninstall.
Aim to keep drives below roughly 80% full. Beyond that, there is less free space for the SLC cache and for wear levelling, and performance declines measurably. Buying more capacity than you currently need is not waste — it is what keeps the drive fast.
Endurance, and why it is not worth worrying about
SSD endurance is rated in terabytes written, and the figures are far beyond typical consumer use. A 1 TB drive commonly carries a rating of several hundred terabytes written. A user writing 30 GB per day — well above normal — would take decades to reach it.
Flash wear is not a practical concern for normal use. Drives are far more likely to be replaced for capacity reasons, or to fail from a controller fault, than to wear out their flash. This does not remove the need for backups: SSD failures tend to be sudden and total, with less warning than the gradual degradation a failing hard drive often gives.
Planning storage for a build
- One NVMe SSD of at least 1 TB as the system drive. This is the configuration that matters, and everything else is optional.
- If your budget is tight, choose capacity over interface generation. A 1 TB Gen3 drive is a better purchase than a 500 GB Gen5 one.
- Add a second drive only when the first is genuinely constraining you. It is the easiest component to add later, with no compatibility considerations.
- Consider a hard drive only for bulk archives — media libraries, backups, files you access rarely. Never for the operating system.
- Check your motherboard: confirm a free M.2 slot wired for PCIe rather than SATA-only, since an NVMe drive in a SATA-wired slot will not be detected at all.
One motherboard caveat worth knowing: M.2 slots frequently share bandwidth with SATA ports or PCIe slots, so populating one can disable another. The board manual documents this and nothing else does.
In short
Buy an NVMe SSD with DRAM, at 1 TB or more, and stop reading the sequential speed figure. The gap between a hard drive and an SSD is the upgrade you will feel; the gap between a good SSD and an excellent one is the upgrade you will read about in benchmarks.
You can compare tracked SSD and hard drive prices across Tunisian retailers in our storage catalogue.