Resource Cheatsheet
A+ Core 1 3.4: Storage Devices
Professor Messer A+ 220-1201 objective 3.4 — hard drives and RPM, SSDs, PCIe and NVMe, SAS, mSATA and M.2 keying, flash memory formats, and optical drives.
- Updated
- Reading time
- 5 min read
- Detail
- A+ Core 1
- Detail
- Storage Devices
On this page
In one line: non-volatile storage ranges from mechanical hard drives (platters, RPM-driven latency) through SSDs and PCIe-connected NVMe (far past SATA’s 6 Gbps ceiling), SAS for fast drive arrays, M.2 as the now-dominant cable-free interface, to flash memory and optical discs for portable and archival storage.
Companion to: Professor Messer, CompTIA A+ 220-1201 Core 1, objective 3.4 (Storage Devices). The full version is the Storage Devices class notes; the section overview is the Section 3 sheet.
Hard drives
| Component | Role |
|---|---|
| Platter | Spinning disk holding the data |
| Spindle | Motor spinning the platter(s) |
| Actuator + arm | Moves the read/write head |
| Read/write head | Reads/writes the platter surface |
- RPM: 5,400 / 7,200 / 10,000 / 15,000 — higher RPM = lower latency.
- Multiple platters = a head/arm on both sides of each.
- Form factors: 3.5” (desktop) · 2.5” (laptop) · SSDs use a different 22 mm form.
- All mechanical parts can fail — the core hard-drive reliability weakness.
SSD → PCIe → NVMe
| Step | What changed |
|---|---|
| HDD → SSD | Non-volatile memory, no moving parts, many times faster |
| SSD outgrows SATA | SATA’s 6 Gbps ceiling becomes the bottleneck |
| PCIe-connected storage | SSD wired directly to PCI Express (adapter card or M.2) for far more throughput |
| AHCI | Advanced Host Controller Interface — the older, SATA-era data-movement standard |
| NVMe | Non-Volatile Memory Express — low latency, connects directly to PCIe, works even in laptops |
| M.2 NVMe | ~20 Gbps theoretical, vs SATA’s 6 Gbps |
Watch the numbers: a single PCIe lane runs ~8 Gbps (gen 3) or ~16 Gbps (gen 4) — not tens of Gbps per lane. High aggregate figures (e.g. ~64 Gbps) come from a 4-lane (x4) link, the typical NVMe configuration, not one lane alone.
SAS (Serial Attached SCSI)
| Point | Detail |
|---|---|
| What | Serialised SCSI protocol for spinning hard drives |
| Speed | ~22.5 Gbps (matches 24G SAS / SAS-4’s published line rate) |
| Connector | Looks like SATA (data one side, power the other, same form factor) but is deliberately different — can’t be cross-plugged |
| Use case | Large arrays of spinning hard drives |
mSATA and M.2
| mSATA | M.2 | |
|---|---|---|
| Full name | Mini SATA | — |
| Role | Stopgap, smaller SATA form factor | Now dominant interface |
| Cables | Still SATA cabling, smaller | None — plugs directly into the slot |
| Speed ceiling | SATA-level | Full PCIe speed available |
M.2 keying: notches at the connector end —
| Key | Meaning |
|---|---|
| B key | One position |
| M key | Another position |
| B+M | Fits either type of slot |
Check the slot’s supported key before buying a drive — a B-keyed-only slot often means SATA-level speed over M.2, not NVMe.
Flash memory
- Based on EEPROM — non-volatile, but with a limited number of write cycles; once exhausted, no more writes (may still read).
- Not reliable as sole backup/archive media — limited writes plus easy to lose. Keep a second copy elsewhere.
- Formats: USB flash drive (most common) · CF (CompactFlash, original/larger) · SD · miniSD / microSD · xD-Picture Card (older cameras).
Optical drives
- Store data as microscopic laser-written bumps.
- Slow vs HDD/SSD, but compact and good for archiving.
- Formats: CD-ROM, DVD-ROM, Blu-ray. Built-in or external (usually USB) readers.
🔐 Security notes
- Physical destruction is the defensible end-of-life method for mechanical HDDs — moving parts fail unpredictably, but a destroyed platter is very hard to recover data from.
- NVMe doesn’t automatically inherit SATA-era security assumptions — confirm full-disk encryption and secure-erase are genuinely supported and configured for NVMe specifically.
- EEPROM write exhaustion is a silent failure mode — a flash drive can stop accepting new data while still reading fine.
- Small flash media cuts both ways: easy to lose (data-loss risk) and easy to smuggle (exfiltration risk) — port control and removable-media policy apply directly.
- SAS/SATA’s deliberate connector mismatch is a “fail safe” design pattern worth recognising elsewhere.
- Old optical archives can hold forgotten sensitive data, well outside live-system data governance tooling.
Practice drills
1. How does RPM affect a hard drive's performance?
Higher RPM = lower latency — the wanted data on the platter reaches the read/write head sooner.
2. Why did SSDs need to move beyond SATA?
SATA’s 6 Gbps ceiling became the bottleneck — SSDs were capable of more.
3. What does NVMe stand for, and why is it faster?
Non-Volatile Memory Express. It connects directly to PCIe, bypassing the older AHCI/SATA model, for lower latency and higher throughput.
4. Roughly how fast is SAS, and what protocol does it serialise?
~22.5 Gbps, serialising the SCSI protocol.
5. Why are SAS and SATA connectors different if the drives look so similar?
Deliberately, to prevent accidentally plugging a SATA drive into a SAS setup or vice versa.
6. What does M.2 keying (B key / M key) actually indicate?
Which type of connectivity the slot and drive support — a mismatched key means the drive physically won’t work in that slot.
7. What's EEPROM's core limitation?
A limited number of write cycles — beyond that, no more writes (though it may still read).
8. Why shouldn't a flash drive be your only backup?
Limited write endurance and easy to lose — both argue for a second copy elsewhere.
Key takeaways
- Hard drives: platters + RPM-driven latency; SSDs: no moving parts, much faster.
- SATA’s 6 Gbps ceiling pushed storage onto PCIe directly — that’s NVMe, reaching ~20 Gbps over M.2.
- SAS (~22.5 Gbps) serialises SCSI for fast hard drive arrays, with connectors deliberately different from SATA.
- M.2 is now dominant, cable-free — but check B/M keying before buying a drive.
- Flash (EEPROM) has a write limit; optical is slow but good for archiving.