Domain 3 of 5 · Chapter 1 of 4

RAM, CPUs, and Storage

Match first: the three compatibility gates

A customer drops a box of parts on the bench and asks you to build a PC. Before any of it matters, three questions decide whether the parts can even work together: does the CPU fit the board, does the memory fit the board, and does the drive fit the board. Every choice in this subtopic passes through one of three compatibility gates, and only after a part clears its gate does performance enter the conversation.

The three gates

  • CPU gate: the processor must use the board's socket and be supported by its chipset and firmware, and it must have a cooler and thermal paste to shed heat.
  • RAM gate: the memory must be the DDR generation the slots accept, in the right physical module (DIMM for desktops, SO-DIMM for laptops), and either ECC or non-ECC to match the platform.
  • Storage gate: the drive must use an interface the board offers (SATA or NVMe over PCIe) and a form factor that physically mounts (a 2.5-inch bay or an M.2 slot).

The figure below sets the three gates side by side with what each one has to match. It also draws RAID level as a third box under Storage, which is the redundancy and speed choice you make after a drive has already cleared its gate, not part of the fit test itself.

The gates are independent: a top-tier CPU does nothing if the memory is the wrong generation, and the fastest NVMe drive is dead weight in a board with no PCIe-wired M.2 slot. This is why an A+ question that lists specs is usually testing a fit, not a benchmark.

What lives elsewhere

This subtopic is the internal compute and storage parts themselves. The cables and connectors that wire them (the SATA data cable, the drive power lead) are cables and connectors, and the board and power supply those parts plug into are motherboards and power. Laptop-specific versions of these same parts, such as SO-DIMM memory and M.2 storage in a thin chassis, appear again in mobile device hardware. Installing and configuring RAM, CPUs, and storage is the A+ Core 1 hardware objective[1].

Every build clears three compatibility gates CPU Socket family (LGA / PGA) Chipset + BIOS support Cooler + thermal paste RAM DDR generation (3 / 4 / 5) DIMM or SO-DIMM ECC or non-ECC Storage Interface (SATA / NVMe) Form factor (2.5in / M.2) RAID level (0 / 1 / 5 / 10)
Three compatibility gates: the CPU matches its socket and chipset, RAM matches its DDR generation and form factor, and storage matches its interface and form factor.

RAM: generations, form factor, channels, and ECC

Start with the rule that governs every memory purchase: the DDR generation the board takes is fixed, and you cannot substitute another. System memory is DDR SDRAM (double data rate synchronous dynamic RAM), and DDR3, DDR4, and DDR5 are keyed so a module physically will not seat in the wrong slot.

Generations

Each generation raises the data rate, measured in MT/s (mega-transfers per second), and lowers the operating voltage, so newer memory moves more data for less power. The three cannot be mixed in one system because the memory controller supports a single generation.

Generation Voltage Typical data rate DIMM / SO-DIMM pins
DDR3 1.5 V (1.35 V for DDR3L) ~800 to 2133 MT/s 240-pin / 204-pin
DDR4 1.2 V ~1600 to 3200 MT/s 288-pin / 260-pin
DDR5 1.1 V 4800 MT/s and up 288-pin / 262-pin

DDR4 and DDR5 desktop modules both have a 288-pin edge, yet the key notch sits in a different spot on each, so they are not interchangeable even though the pin count matches. That collision is a favorite exam trap.

Form factor: DIMM versus SO-DIMM

The full-size DIMM (dual inline memory module) goes in desktops and servers; the shorter SO-DIMM (small outline DIMM) is the laptop, mini-PC, and all-in-one version of the same generation. A DIMM and a SO-DIMM are never cross-compatible in a slot, so a laptop upgrade needs SO-DIMM of the correct DDR generation.

Channels

The memory controller reads across multiple channels at once. Installing one identical module per channel enables dual channel, which roughly doubles usable bandwidth over a single stick; boards built for it can run quad channel with four modules. Boards mark the paired slots by color, or name them in the manual (often the second slot of each channel gets filled first). A single stick, or a mismatched pair, falls back toward single-channel bandwidth, and mixed-speed modules run at the slowest one's rate. The figure below shows that population pattern in the slots: one module per channel, in the paired slots the board marks.

ECC versus non-ECC

ECC (error-correcting code) memory carries an extra chip that detects and corrects single-bit errors as they happen, which servers and workstations use to avoid silent data corruption. ECC only works when the CPU and motherboard support it, so an ECC module in a typical consumer board buys you nothing. Mainstream desktops and laptops use non-ECC memory. Note that DDR5's on-die ECC is not the same feature: it protects the chip's own cells internally and does not report or correct errors to the system the way a true ECC DIMM does. Comparing memory types and installing them is the A+ Core 1 RAM objective[1].

Dual channel needs one module per channel Channel A A1 empty A2 module Channel B B1 empty B2 module
Dual channel needs one identical module in each channel; slot colors mark the pair to fill, often the second slot of each channel.

CPUs: sockets, seating, and staying cool

The first fact about any CPU install is where the pins live, because it decides which part you can destroy with a careless move. LGA puts the pins in the socket; PGA puts them on the chip.

Socket type: LGA versus PGA

An LGA (land grid array) socket holds an array of spring pins, and the CPU shows flat gold pads (lands) that press onto them; Intel's mainstream sockets and AMD's newer AM5 are LGA. A PGA (pin grid array) chip carries the pins itself and drops them into holes in the socket, as on older AMD sockets like AM4. On an LGA system a bent pin is damage to the motherboard; on PGA it is damage to the CPU.

Compatibility is socket plus chipset plus firmware

A matching socket is necessary but not sufficient. The board's chipset and BIOS must also support the specific chip, because a newer CPU can share a socket with an older board yet need a firmware update before it will POST (power-on self-test). Always check the board maker's CPU support list, not just the socket name.

Seating the chip

A CPU installs one way, marked by a small triangle or notch that lines up with a matching mark on the socket. It should settle in under its own weight with zero force; forcing a misaligned chip bends pins. Lift the retention arm, align the corner mark, lower the chip flat, then close the arm to lock it. The figure below runs the whole install as five steps, from matching the socket through mounting the cooler.

Thermal paste and cooling

Between the CPU's metal lid and the cooler base sits a thin, even layer of thermal paste (thermal compound), which fills microscopic air gaps so heat can cross into the cooler. Too much paste insulates and can ooze onto the socket; none at all leaves an air gap that causes overheating and thermal shutdowns. Cooling comes in two forms:

  • Air cooler: a finned heatsink with a fan, cheap and reliable, with no liquid to leak. It handles most CPUs.
  • Liquid all-in-one (AIO): a sealed loop where a pump moves coolant to a radiator, shedding more heat for hot, high-core-count, or overclocked chips, and fitting cases where a tall air tower will not.

Both still need thermal paste at the chip. If a build powers on but shows no display, confirming whether the CPU, memory, or something else is at fault is hardware and network troubleshooting. Selecting and installing a compatible CPU is the A+ Core 1 CPU objective[1].

1. Match the CPU to the socket and chipset 2. Lift the retention arm, align the corner mark 3. Seat the chip flat, close the arm, no force 4. Apply a thin, even layer of thermal paste too much insulates; do not skip it 5. Mount the cooler, connect the fan header
CPU install order: match the socket and chipset, align the corner mark, seat with no force, apply a thin paste layer, then mount the cooler.

Storage: HDD, SSD, SATA, NVMe, and form factors

Two questions rank every drive: what stores the bits, and what moves them to the rest of the system. The first splits hard disk drives from solid-state drives; the second splits SATA from NVMe. Keep them separate, because the form factor of a drive does not tell you its interface.

Media: HDD versus SSD

A hard disk drive (HDD) stores data on spinning magnetic platters read by a moving head. Its baseline speed tracks spindle speed: a 7200 RPM drive is faster than a 5400 RPM drive, while 5400 RPM runs cooler, quieter, and on less power, which is why laptops and bulk storage favor it. A solid-state drive (SSD) stores data in flash memory with no moving parts, giving far lower latency, silent operation, and much better shock resistance. HDDs still win on cost per terabyte, so a common build boots from an SSD and keeps an HDD for large files.

Interface: SATA versus NVMe

The interface sets the speed ceiling. SATA (Serial ATA) III runs at 6 Gb/s, roughly 550 to 600 MB/s of real throughput, and that ceiling applies to any drive on the bus, HDD or SSD. NVMe (Non-Volatile Memory Express) is a protocol that connects the SSD straight to the CPU over PCIe (PCI Express) lanes instead, so a typical NVMe drive reaches 3,500 MB/s and up, several times a SATA SSD's ceiling. The board's firmware also sets the mode its SATA ports run in: AHCI (Advanced Host Controller Interface) is the normal mode for a single drive, giving it native command queuing (the drive reordering queued commands) and hot-plug; IDE is the legacy compatibility mode; and RAID mode is the one that loads the onboard RAID option ROM, the firmware routine that builds an array during POST.

Form factor is a separate axis

Attribute HDD SATA SSD NVMe SSD
Interface SATA SATA (6 Gb/s) PCIe lanes
Typical max throughput ~100 to 250 MB/s ~550 MB/s 3,500 MB/s and up
Form factors 3.5in / 2.5in 2.5in / M.2 M.2 / add-in card
Moving parts Platters + heads None None
Best use Cheap bulk capacity Value SSD upgrade Fastest boot and workload disk

Desktop hard drives use the 3.5-inch form factor; 2.5-inch bays hold laptop hard drives and SATA SSDs; M.2 is the small gumstick card that mounts flat on the board (commonly the 2280 size, 22 mm by 80 mm). Here is the gotcha the objective loves: a 2.5-inch drive is always SATA, but an M.2 slot may be wired for SATA, for NVMe, or for both, so an M.2 stick can speak either protocol. A slot's keying (B-key, M-key, or B+M) and the manual tell you which it accepts; an NVMe drive in a SATA-only M.2 slot will not run. The data and power cabling that connects a SATA drive belongs to cables and connectors. Choosing storage devices is the A+ Core 1 storage objective[1].

RAID levels: 0, 1, 5, and 10

Picture a small file server with four drives where one dead disk must not stop the business: choosing how to combine those drives is a RAID decision. Once more than one drive is involved, RAID (redundant array of independent disks) groups them for speed, redundancy, or both. The A+ set is levels 0, 1, 5, and 10, and the decision tree further down this page walks the choice; this section pins the facts each level turns on and the one thing candidates most often get wrong.

The four A+ levels

  • RAID 0 (striping): splits data across two or more drives for the combined speed and capacity, with no parity or mirror. Any single drive failing destroys the whole array, so it actually raises the risk of loss versus one drive (Microsoft: RAID levels[2]). It fits scratch space, not anything you need to keep.
  • RAID 1 (mirroring): writes the same data to two drives, so the array survives one failure and rebuilds by copying the survivor. Usable capacity is one drive, 50 percent of the raw total.
  • RAID 5 (striping with distributed parity): needs at least three drives, survives one failure, and rebuilds the lost data from parity spread across the members (Microsoft: mirror and parity resiliency[3]). Usable capacity is the total minus one drive, a more space-efficient way to get redundancy than mirroring.
  • RAID 10 (a stripe of mirrors): needs at least four drives and combines the speed of striping with the safety of mirroring, tolerating one failure per mirror. Usable capacity is 50 percent, the same overhead as RAID 1.

RAID is not a backup

The single most important RAID point on the exam: redundancy is not a backup. RAID keeps a system running when a disk dies, but deletions, corruption, ransomware, and controller faults hit every drive in the array at once, so you still need separate backups. Treating a RAID array as your only copy is the classic mistake.

How the exam frames RAM, CPUs, and storage

Questions on this page name a requirement and ask which part or level meets it, and the wrong answers are the options that ignore one stated constraint.

Question stem says Right answer Common wrong answer
Needs speed, data is disposable RAID 0 (striping) RAID 1, wasting a drive on a mirror it does not need
Two drives, must survive a failure RAID 1 (mirror) RAID 5, which needs at least three drives
Three or more drives, wants redundancy and capacity RAID 5 (parity) RAID 0, which has no redundancy
Four-plus drives, wants speed and redundancy RAID 10 RAID 5, slower on writes due to parity
M.2 drive runs at SATA speed The slot is SATA-wired, or the drive is a SATA M.2 Assuming every M.2 is NVMe
PC will not take more RAM The memory is the wrong DDR generation or maxed Buying faster RAM of the wrong generation

Each row maps back to the compatibility and RAID rules above: name the level or part the requirement demands, and reject the option that ignores a stated constraint (the drive count, the need for redundancy, the interface). Configuring a RAID array is part of the A+ Core 1 storage objective[1].

RAID levels at a glance

AttributeRAID 0RAID 1RAID 5RAID 10
Minimum drives2234
Fault toleranceNone1 drive1 drive1 per mirror
Usable capacity100% (sum)50%All but one drive50%
What it givesSpeed and capacityRedundancyRedundancy and capacitySpeed and redundancy
On a drive failureWhole array lostCopy from the mirrorRebuild from parityCopy the surviving mirror

Decision tree

Must the array survive a drive failure? No Yes RAID 0 stripe, no redundancy Do you have only two drives? Yes No RAID 1 mirror, 2 drives, 50% usable Need top speed plus redundancy? Yes No RAID 10 mirror + stripe, min 4 RAID 5 stripe + parity, min 3, survives one
Cheat sheet

Sharp facts the exam loves — give these one last read before exam day.

Cheat sheet

Sharp facts the exam loves — scan these before test day.

Each DDR generation fits only its own slot

DDR3, DDR4, and DDR5 modules are keyed with the notch in a different spot, so a stick physically will not seat in a slot built for another generation, and the memory controller supports only one generation. DDR4 and DDR5 DIMMs even share a 288-pin edge, yet the notch position still differs, so they are not interchangeable. Confirm the board's generation before ordering memory, because the fastest DDR5 kit is useless in a DDR4 board.

Trap Assuming DDR4 and DDR5 interchange because both are 288-pin DIMMs; the key notch sits in a different position and the controller accepts only one generation.

1 question tests this
DDR voltage drops as the generation climbs

Standard operating voltage falls each generation: DDR3 runs at 1.5 V (DDR3L at 1.35 V), DDR4 at 1.2 V, and DDR5 at 1.1 V, which is part of how newer memory raises bandwidth while holding power in check. The data rate moves the other way, from roughly 800 to 2133 MT/s (mega-transfers per second) on DDR3 up to 4800 MT/s and beyond on DDR5.

DIMM is for desktops, SO-DIMM is for laptops

A full-size DIMM (dual inline memory module) goes in desktop and server boards, while the shorter SO-DIMM (small outline DIMM) is the laptop and small-form-factor version of the same generation. The two are not cross-compatible in a slot, so a laptop upgrade needs SO-DIMM of the correct DDR generation. All-in-one PCs and mini PCs often use SO-DIMM to save space.

Trap Putting a desktop DIMM in a laptop; the laptop slot only accepts the shorter SO-DIMM even when the DDR generation matches.

1 question tests this
Dual channel needs matched modules in the paired slots

Installing one identical module in each memory channel lets the controller run dual channel, which roughly doubles memory bandwidth over a single stick; capable boards extend this to quad channel with four modules. The slots for each channel are color-coded or named in the manual, often the second slot of each channel, and the modules should match in size and speed. A single stick, or two mismatched sticks, drops the system back toward single-channel bandwidth.

Trap Putting both sticks in one channel's two slots; that leaves the array single-channel, so use one slot from each channel per the board's color coding.

1 question tests this
ECC memory corrects single-bit errors but needs platform support

ECC (error-correcting code) memory carries an extra chip that detects and fixes single-bit errors in real time, which is why servers and workstations that cannot tolerate silent corruption use it. It only works when the CPU and motherboard support ECC, so dropping an ECC module into a typical consumer desktop gives you no error correction. Mainstream desktops and laptops run non-ECC memory, trading that protection for lower cost.

Trap Assuming DDR5 on-die ECC turns every DDR5 module into ECC memory; on-die ECC only protects the chip's cells internally and does not report or correct errors to the system the way a true ECC DIMM does.

1 question tests this
Mixed memory runs at the slowest module's rating

When you mix modules of different speeds, the memory controller clocks the whole set to the slowest stick's supported rate, and mixing sizes or timings can force single-channel operation. For predictable dual-channel performance, install a matched kit that was sold and tested together. Faster memory in the mix does not raise the baseline; it just runs slower to stay compatible.

2 questions test this
LGA puts pins on the socket, PGA on the chip

An LGA (land grid array) socket holds the delicate pins while the CPU shows flat contact pads, so Intel mainstream sockets and AMD's newer AM5 are LGA. A PGA (pin grid array) chip carries the pins itself and drops into holes in the socket, as on older AMD sockets like AM4. The distinction decides where a bent pin lives and how carefully you handle each part during install.

Trap Treating the CPU as the damaged part when pins bend on an LGA system; there the pins are in the motherboard socket, not on the chip, so the board is what is bent.

8 questions test this
Thermal paste goes on thin, and too much insulates

Thermal paste fills the microscopic gaps between the CPU's heat spreader and the cooler base so heat can cross into the cooler; a thin, even layer is the goal. Too much paste acts as an insulator and can ooze onto the socket, while none at all leaves an air gap that causes overheating and thermal shutdowns. Reseating a cooler means cleaning off the old paste and applying fresh compound.

Trap Applying a thick blob of paste to be safe; excess compound insulates and can spill onto pins, so a thin even layer transfers heat better.

10 questions test this
A matching socket still needs chipset and BIOS support

A CPU has to fit the socket and be supported by the motherboard's chipset and firmware, because a newer chip can share a socket with older boards yet need a BIOS update before it will POST. Check the board maker's CPU support list, not just the socket name, before buying. A supported socket with stale firmware can leave the system dead until you flash the BIOS with a compatible chip.

Trap Assuming a socket match alone guarantees a CPU works; the same socket can need a BIOS update first, so an unsupported firmware version will not boot the chip.

Align the CPU by its corner marker and never force it

A CPU seats only one way, marked by a small triangle or notch that lines up with the matching mark on the socket, and it should settle in under its own weight with zero force. Forcing a misaligned chip bends pins, whether on the chip (PGA) or in the socket (LGA). Lower the retention arm to lock it once it sits flat.

1 question tests this
7200 RPM drives are faster; 5400 RPM run cooler and quieter

A hard disk drive's spindle speed sets its baseline performance, so a 7200 RPM drive reads and writes faster than a 5400 RPM drive of the same design. The 5400 RPM class runs cooler, quieter, and on less power, which is why laptops and bulk storage favor it, while 7200 RPM suits performance desktops. Spindle speed matters only for HDDs; an SSD has no platters to spin.

Trap Treating RPM as an SSD spec; solid-state drives have no spindle, so RPM is meaningless for them.

SSDs have no moving parts, so they beat HDDs on speed and shock

A solid-state drive stores data in flash memory with no platters or heads, giving far lower latency, faster boot and load times, silent operation, and much better shock resistance than a hard disk drive. An HDD still wins on cost per terabyte, which is why bulk and archival storage often stays on spinning disks. A common upgrade is to boot from an SSD and keep an HDD for large files.

SATA III caps a drive near 600 MB/s no matter the media

The SATA (Serial ATA) III bus runs at 6 Gb/s, which works out to roughly 550 to 600 MB/s of real throughput, and that ceiling applies whether the drive is a hard disk or a SATA SSD. A fast SATA SSD saturates the bus, so the only way past the limit is a different interface, which is exactly what NVMe over PCIe provides.

NVMe rides PCIe lanes to reach multi-gigabyte speeds

NVMe (Non-Volatile Memory Express) is a protocol that connects the SSD straight to the CPU over PCIe (PCI Express) lanes instead of the SATA bus, so a typical NVMe drive reaches 3,500 MB/s and up, several times a SATA SSD's ceiling. The trade is that NVMe needs an M.2 slot (or add-in card) wired for PCIe. For boot disks and heavy workloads, NVMe is the clear performance pick.

Trap Assuming any M.2 slot delivers NVMe speed; a slot wired only for SATA will not run an NVMe drive at all, so the slot has to provide PCIe lanes.

1 question tests this
An M.2 drive can be SATA or NVMe, so check the slot

M.2 is only a physical form factor, so an M.2 stick may speak either SATA or NVMe, and the two are not automatically interchangeable in a given slot. A slot's keying (B-key, M-key, or B+M) and the board manual tell you which interfaces it accepts. Match the drive's protocol to what the slot supports, or the drive runs at the wrong speed or not at all.

Trap Assuming every M.2 drive is NVMe; M.2 is just the shape, and a SATA M.2 drive behaves like a SATA drive despite the M.2 form factor.

1 question tests this
Know the physical form factors: 3.5in, 2.5in, and M.2

Desktop hard drives use the 3.5-inch form factor, while 2.5-inch bays hold laptop hard drives and SATA SSDs, and M.2 is the small gumstick card that mounts flat on the board (commonly the 2280 size, 22 mm by 80 mm). Form factor is about physical fit and mounting, separate from the SATA-versus-NVMe interface question. A 2.5-inch drive is always SATA; only M.2 or an add-in card carries NVMe.

1 question tests this
RAID 0 stripes for speed with zero redundancy

RAID 0 splits data across two or more drives (striping) to add their speed and capacity, but it stores no parity or mirror, so losing any single drive destroys the entire array. It fits scratch space and workloads that value throughput over safety. Because a single failure wipes everything, RAID 0 actually increases the chance of data loss versus one drive.

Trap Treating RAID 0 as safe because it spans multiple drives; it has no redundancy at all, and one failed drive loses the whole array.

4 questions test this
RAID 1 mirrors two drives for redundancy

RAID 1 writes the same data to two drives (mirroring), so the array keeps running if one drive fails and you rebuild by copying from the survivor. The cost is capacity: usable space equals one drive, or 50 percent of the raw total. It is the simplest way to protect a two-drive system against a single disk failure.

2 questions test this
RAID 5 stripes with distributed parity across three or more drives

RAID 5 stripes data with parity spread across at least three drives, so it survives one drive failure and rebuilds the lost data from parity, while usable capacity is the total minus one drive's worth. It balances redundancy and space more efficiently than mirroring, which is why it is common for file servers. A second drive failing before the rebuild finishes loses the array.

Trap Assuming RAID 5 survives two simultaneous drive failures; it tolerates only one, and a second failure during rebuild loses the array.

11 questions test this
RAID 10 mirrors then stripes for speed plus redundancy

RAID 10 stripes across mirrored pairs, needing at least four drives, so it delivers both the speed of striping and the fault tolerance of mirroring, tolerating a drive failure in each mirror. Usable capacity is 50 percent of the raw total, the same overhead as RAID 1. It is the go-to when a workload needs high performance and redundancy and can afford the drives.

3 questions test this
RAID protects against drive failure, not deletion or corruption

RAID keeps a system available when a disk fails, but it is not a backup, because deletions, corruption, ransomware, and controller faults propagate across the array immediately. You still need separate backups to recover from those events. Treating RAID as your only copy of the data is a classic mistake the exam probes.

Trap Relying on a redundant RAID array as the backup; RAID does not protect against deletion, corruption, or malware, which hit every drive at once.

1 question tests this
Tighten a CPU cooler gradually in a diagonal cross pattern

Secure a CPU cooler by turning its retention screws only a few turns each in a diagonal cross (X) pattern, cycling around until all are snug, so mounting pressure lands evenly across the CPU heat spreader for uniform thermal-paste contact. Fully tightening one corner first tilts the cooler and leaves poor contact. A cooler that is loose or unevenly mounted loses that contact and can overheat and shut the system down within minutes of boot.

Trap Fully tightening one corner screw before the others, which tilts the cooler off the die.

5 questions test this
Set the UEFI SATA mode to RAID for an array, AHCI for a single drive

The motherboard's onboard RAID utility only appears if you first set the SATA controller mode to RAID in UEFI/BIOS; left on AHCI or IDE, the RAID option ROM never loads and no array can be built during POST. For a normal single SATA drive or SSD, AHCI is the correct mode, enabling native command queuing and hot-plug for the best performance. The mode is a firmware setting, not something the drive or the operating system selects on its own.

Trap Leaving the SATA mode on AHCI or IDE and expecting the RAID utility to appear at POST.

4 questions test this

References

  1. CompTIA A+ (Core 1 and Core 2) Certification
  2. SQL Server Drive Configurations: RAID 0/1/5/10 levels Blog
  3. Fault tolerance and storage efficiency: Storage Spaces mirror and parity