RAM & Storage: Specs, Speed, and Form Factors

You already know that RAM is fast and volatile, and that storage is slower and persistent. The previous lesson covered the basics — what each component is, and the compatibility rules that let you pair them with a motherboard. This lesson goes deeper: the specs that determine how fast and how much, the form factors that differ between desktops and laptops, and the NAND types that determine how long an SSD lasts.

RAM generations in detail

RAM comes in generations — DDR4, DDR5, and LPDDR. Each generation is a successor to the last, bringing higher transfer rates and lower voltages. They are not backward-compatible: the notch that keys the module into its slot is in a different position for each generation.

The headline spec is transfer rate, measured in megatransfers per second (MT/s):

• DDR4 stock speeds typically run 2133–3200 MT/s.
• DDR5 starts at 4800 MT/s and goes well beyond — roughly double DDR4 in bandwidth.

The other spec you'll see on memory modules is CAS latency (CL), which measures the delay in clock cycles before the RAM responds to a request. Lower CL is faster — but because DDR5 runs faster clock cycles, a DDR5 module with a higher CL number can still have lower actual latency than DDR4.

LPDDR — the mobile variant

LPDDR (Low Power DDR) is the laptop and mobile variant of the DDR standard. It runs at a lower voltage than standard DDR to extend battery life, and it is typically soldered directly onto the motherboard rather than installed in removable slots. If an LPDDR module fails, you don't swap a stick — you replace the board.

RAM form factors

The physical module that slots into a motherboard comes in two sizes:

• DIMM (Dual Inline Memory Module) — the full-size format for desktops. A DDR5 DIMM is 288 pins.
• SO-DIMM (Small Outline DIMM) — roughly half the length, designed for laptops and small-form-factor desktops. A DDR5 SO-DIMM is 262 pins.

The two formats don't physically swap into each other's slots. When you're upgrading RAM, confirm which form factor the system needs.

Dual-channel memory

Most modern motherboards and CPUs support dual-channel mode: when two matched memory sticks are installed in the correct paired slots (typically labelled A2 and B2, or colour-coded), the system can access both simultaneously, effectively doubling the memory bandwidth.

The practical upshot: 2 × 8GB provides better real-world performance than 1 × 16GB, even though the total capacity is identical. For the exam, what matters is that dual-channel requires matched sticks in the correct slots.

HDD speed

Hard disk drives (HDDs) store data on spinning magnetic platters. The speed at which those platters rotate — measured in RPM (revolutions per minute) — directly affects how quickly the read/write head can reach data:

• 5400 RPM — the slower, quieter standard found in many laptops and external drives.
• 7200 RPM — faster, more common in desktop HDDs and performance-oriented laptop drives.

Higher RPM means shorter average seek time and better sustained transfer speed. That said, even a 7200 RPM HDD is dramatically slower than any modern SSD — HDDs are relevant for large, cheap bulk storage rather than system performance.

SSD NAND types

Inside a NAND flash SSD, data is stored in cells. The number of bits packed into each cell determines capacity, cost, speed, and how long the drive lasts:

| Type | Bits per cell | Endurance | Cost | Common use | |------|--------------|-----------|------|------------| | SLC (Single-Level Cell) | 1 | Highest | Most expensive | Enterprise, write-intensive | | MLC (Multi-Level Cell) | 2 | Good | Mid-range | Consumer performance | | TLC (Triple-Level Cell) | 3 | Moderate | Low | Mainstream consumer SSDs | | QLC (Quad-Level Cell) | 4 | Lowest | Cheapest | High-capacity, light-write |

The rule is simple: more bits per cell = lower cost per gigabyte but shorter lifespan. Most consumer SSDs you'll encounter are TLC. QLC drives make sense for cold storage or read-heavy workloads where you're not constantly rewriting data.

Storage form factors

How a storage device physically connects to (or installs in) a system depends on its form factor.

3.5-inch — the standard desktop HDD footprint. Mounts in drive bays inside the case. Needs a SATA data cable and SATA power from the PSU.

2.5-inch — the laptop HDD and SATA SSD form factor. Smaller than 3.5-inch and also used in desktops (with an adapter bracket). Still needs a SATA data cable and power.

M.2 — a compact stick-shaped drive that plugs directly into an M.2 slot on the motherboard — no cables needed. This is the form factor used by most modern NVMe SSDs (and some SATA SSDs).

M.2 drives come in different lengths, indicated by a four- or five-digit code (e.g. 2242, 2260, 2280). The first two digits are the width in millimetres (22 mm for all mainstream drives); the last two or three are the length. 2280 is by far the most common — 80mm long, fits nearly every M.2 slot. Always confirm the slot length against the drive spec.

Putting it together

RAM and storage serve complementary roles:

• RAM is the CPU's fast scratch pad. It's volatile (gone when power is cut), fast (nanoseconds), and limited in capacity (typically 8–64 GB in a consumer system).
• Storage is the long-term library. It's non-volatile (persists without power), slower (microseconds to milliseconds), and far larger (typically hundreds of gigabytes to multiple terabytes).

When you upgrade a sluggish system, knowing which bottleneck to address matters: a system that thrashes its page file constantly needs more RAM; a system that boots slowly or loads applications slowly needs faster storage. Both problems feel like "slowness" but have different fixes.

The check questions below will test the specs, form factors, and NAND types from this lesson.