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Memory and Storage FAQs

Memory and storage choices decide how a system copes with power loss, temperature and years of writes. These FAQs cover RAM and DIMM types, SSD and HDD technology, NVMe and SATA, flash endurance, RAID and network storage.

38 answers Search all FAQs
Topics 12
MEMORY · SYSTEM MEMORY

What Is RAM?

RAM (random-access memory) is a computer’s short-term working memory. It holds the operating system, programs and data the processor is using right now, so they can be read and changed in nanoseconds. RAM is volatile, so it is cleared when the power goes off, and it is separate from storage such as an SSD.

6 MIN
STORAGE · DRIVE TYPES

SSD vs HDD: What Is the Difference?

An HDD (hard disk drive) stores data magnetically on spinning platters read by a moving head. An SSD (solid-state drive) stores it on flash chips with no moving parts. SSDs are much faster, quieter and more tolerant of shock, vibration and heat. HDDs still cost less per terabyte, so they suit large archives and video retention.

6 MIN
STORAGE · SSD INTERFACES

What Is a SATA SSD?

A SATA SSD is a solid-state drive that connects over the Serial ATA interface, the same link used by hard drives. It stores data on NAND flash with no moving parts and tops out at around 550 MB/s. It comes as a 2.5-inch drive, an mSATA or M.2 card, or a SATA DOM.

6 MIN
STORAGE · PERFORMANCE

What Is IOPS?

IOPS (input/output operations per second) measures how many separate read and write requests a drive or storage system completes each second. It matters most for small, random access such as databases and operating systems. A 7,200 rpm hard drive manages around 100 random IOPS, a SATA SSD tens of thousands and an NVMe SSD hundreds of thousands.

6 MIN
STORAGE · SSD ENDURANCE

What Is SSD TBW?

TBW (terabytes written) is an SSD’s endurance rating: the total amount of data the manufacturer guarantees can be written to the drive over its warranty before the flash wears out. A 1 TB SSD rated at 600 TBW, for example, is warranted for 600 TB of writes. DWPD expresses the same limit as full-drive writes per day.

6 MIN
MEMORY AND STORAGE · SERVER SSDS

What Is E1.S?

E1.S is a small, hot-swappable NVMe SSD form factor for servers, short for EDSFF 1U Short. It is a slim ruler-shaped drive about 31.5 mm wide and 111 mm long that slots vertically into the front of a 1U or 2U server, giving more drives, better cooling and easier replacement than M.2.

6 MIN
GPUS AND AI · NVIDIA HOPPER

H100 vs H200: What Is the Difference?

The H100 and H200 are both NVIDIA Hopper data centre GPUs with the same compute cores. The difference is memory: the H200 has 141 GB of HBM3e at 4.8 TB/s, against 80 GB of HBM3 at 3.35 TB/s on the H100 SXM. That lets it hold larger AI models and run memory-bound inference faster.

6 MIN
STORAGE · EMBEDDED FLASH

What Is eMMC Storage?

eMMC storage (embedded MultiMediaCard) is NAND flash memory and its controller packaged in one small chip that is soldered to a device’s circuit board. Defined by JEDEC, it gives phones, tablets, single board computers and embedded modules a low-cost, low-power boot and system drive, typically from 8 to 256 GB, at up to around 400 MB/s.

6 MIN
STORAGE · COMPARISON

eMMC vs SSD: What Is the Difference?

eMMC and SSDs both store data on NAND flash. eMMC is a single chip soldered to the board on a slower 8-bit bus, up to around 400 MB/s, while an SSD is a replaceable drive on SATA or PCIe NVMe, from around 550 MB/s to several GB/s. eMMC costs less and uses less power; SSDs are faster, larger and upgradeable.

6 MIN
EXPANSION · CABLED PCIE

What Is MCIO?

MCIO (Mini Cool Edge IO) is a compact internal connector and cable system that carries PCIe lanes from a motherboard to NVMe drive backplanes, riser cards and accelerators. Defined by SNIA as SFF-TA-1016, it comes in x4, x8 and x16 versions and is built for PCIe 5.0 and 6.0 signaling.

6 MIN
STORAGE · MAINTENANCE

What Is Hot Swapping?

Hot swapping, or hot swap, means removing and replacing a component while the computer keeps running, with no shutdown or restart. A hot-swappable part, such as a drive in a front bay, a redundant power supply or a fan, is designed so it can be pulled and replaced live without damage or lost data.

6 MIN
STORAGE · DATA PROTECTION

What Is a RAID Controller?

A RAID controller is the hardware or software that combines several drives into a RAID array and presents it to the operating system as one logical drive. A hardware RAID controller, or RAID card, has its own processor and cache to handle striping, parity and rebuilds; firmware and software RAID use the host CPU instead.

7 MIN
CONNECTORS · STORAGE

What Is a SATA Connector?

A SATA connector is the flat, L-shaped connector that links a hard drive or SSD to a motherboard. Each drive has two: a 7-pin data connector carrying the Serial ATA signal at up to 6 Gb/s, and a 15-pin power connector supplying 3.3, 5 and 12 V. eSATA is the shielded external version for outside drives.

6 MIN
MEMORY · MODULES

DIMM vs SO-DIMM: What Is the Difference?

A DIMM is the full-size memory module used in desktops, servers and larger industrial boards. A SO-DIMM is the short version, about half the length, used in laptops, mini PCs and compact embedded boards. At the same DDR generation and speed they perform the same; they differ in size, pin count and slot, so they are not interchangeable.

5 MIN
STORAGE · DRIVE ARRAYS

What Is RAID?

RAID (redundant array of independent disks) combines two or more drives so the system sees them as one volume. Depending on the RAID level, it stripes data for speed, mirrors it for redundancy or adds parity so the array survives a drive failure. RAID protects against a failed drive, not against deletion or ransomware, so it is not a backup.

6 MIN
STORAGE · NETWORKED STORAGE

What Is NAS (Network Attached Storage)?

NAS (network attached storage) is a storage device that connects to a network and shares its drives as files with many computers at once. A NAS is a small dedicated computer with its own processor, operating system and drive bays, usually set up as RAID, and it is reached over Ethernet using file protocols such as SMB and NFS.

6 MIN
STORAGE · MEMORY CARDS

What Is a microSD Card?

A microSD card is the smallest SD memory card format, 15 × 11 × 1 mm, defined by the SD Association. It stores data on NAND flash and is used in phones, cameras, drones and many embedded boards. microSD, microSDHC and microSDXC cards differ in capacity and file system, and a passive adapter lets one fit a full-size SD slot.

6 MIN
STORAGE · SOLID-STATE DRIVES

What Is an SSD?

An SSD (solid-state drive) is a storage drive that keeps data on NAND flash memory chips instead of spinning magnetic platters. With no moving parts it reads and writes far faster than a hard drive, draws less power and copes better with shock and vibration. It connects over SATA or over PCIe using NVMe.

6 MIN
MEMORY · MODULES AND SLOTS

What Is a SO-DIMM?

A SO-DIMM (small outline dual in-line memory module), also written SODIMM, is the compact memory module used in laptops, mini PCs, embedded boards and small industrial computers. It is about half the length of a desktop DIMM and uses the same DRAM chips, so it performs the same at the same speed, but neither fits the other’s slot.

6 MIN
STORAGE · NAND FLASH

QLC vs TLC: What Is the Difference?

TLC (triple-level cell) flash stores three bits in each NAND cell and QLC (quad-level cell) stores four. QLC gives more capacity for the money, but each cell survives fewer write cycles and sustained writes slow sharply once the drive’s cache fills. TLC is the safer default for boot drives, logging and recording; QLC suits large, read-mostly data.

6 MIN
STORAGE · NETWORKED STORAGE

What Is iSCSI?

iSCSI (Internet Small Computer Systems Interface) is a protocol that carries SCSI storage commands over standard TCP/IP Ethernet. It lets a computer use a disk on a remote storage system as if it were a local drive, at block level. It is the usual low-cost way to build a SAN without Fiber Channel hardware.

6 MIN
STORAGE · LEGACY TECHNOLOGY

What Is Intel Optane?

Intel Optane was a family of memory and storage products built on 3D XPoint, a non-volatile memory faster and more durable than NAND flash. It came as Optane Memory cache modules, Optane SSDs and Optane Persistent Memory for servers. Intel announced in 2022 that it was winding down the Optane business, so it is discontinued.

6 MIN
STORAGE · NAND AND NOR

What Is Flash Memory?

Flash memory is non-volatile, solid-state memory that keeps its data with the power off. It stores bits as electrical charge in transistor cells and is erased in blocks rather than byte by byte. NAND flash gives the density behind SSDs, eMMC and SD cards, while NOR flash holds firmware and microcontroller code.

6 MIN
MEMORY · DRAM

What Is DRAM?

DRAM, or dynamic random-access memory, is the main memory in almost every computer. Each bit is stored as a charge in a tiny capacitor that leaks, so the memory refreshes itself thousands of times a second. It is dense and cheap per bit, but volatile: it loses its data when power is removed.

6 MIN
STORAGE · MEMORY CARDS

What Is a Compact Flash Card?

A compact flash (CompactFlash, CF) card is a removable flash memory card introduced by SanDisk in 1994. It uses a parallel ATA interface, so a computer can treat it as an IDE hard drive and boot from it. That made CF a long-running boot drive in industrial and embedded systems. CFast is its SATA-based successor.

6 MIN
STORAGE · NAND FLASH

What Is a QLC SSD?

A QLC SSD stores four bits in every NAND flash cell. QLC (quad-level cell) packs more data per chip than SLC, MLC or TLC flash, so capacity is cheaper, but each cell tolerates fewer write cycles and sustained writes are slower. It suits read-heavy storage better than constant logging or recording.

6 MIN
MEMORY · MODULES AND SLOTS

What Is a DIMM?

A DIMM, or dual in-line memory module, is the small circuit board that carries a computer’s RAM chips and plugs into a memory slot on the motherboard. It has separate contacts on each side and a 64-bit data path. SO-DIMM is the shorter version used in laptops and compact industrial boards.

6 MIN
MEMORY · DATA RETENTION

Volatile vs Non-Volatile Memory: What Is the Difference?

Volatile memory needs power to hold data and loses it when the power goes. RAM, both DRAM and SRAM, is volatile. Non-volatile memory keeps data with the power off: flash in SSDs and eMMC, the firmware chip and EEPROM are all non-volatile. Computers use fast volatile memory for working data and non-volatile memory to keep it.

6 MIN
STORAGE · DATA SECURITY

What Is Secure Erase on an SSD?

Secure erase is a command built into SSD firmware that wipes every flash block, including spare and remapped areas the operating system cannot reach. It is the reliable way to sanitize an SSD, because ordinary deleting, formatting or overwriting leaves old data behind. SATA drives use the ATA secure erase or sanitize commands, and NVMe drives use format or sanitize.

6 MIN
STORAGE · MEMORY CARDS

SDHC vs SDXC: What Is the Difference?

SDHC and SDXC are SD card capacity classes. SDHC (Secure Digital High Capacity) cards hold over 2 GB and up to 32 GB and use FAT32. SDXC (Secure Digital eXtended Capacity) cards hold over 32 GB and up to 2 TB and use exFAT. Speed is set separately, by the bus and speed class, not by the name.

6 MIN
STORAGE · DRIVE INTERFACES

SAS vs SATA: What Is the Difference?

SAS and SATA are both serial drive interfaces. SAS (Serial Attached SCSI) is the server version: 12 or 24G speeds, full duplex, dual ports for failover and long cables. SATA runs at 6 Gb/s with one port and suits desktops, embedded systems and cost-sensitive storage. SAS controllers accept SATA drives, but not the other way round.

6 MIN
MEMORY · STORAGE

Memory vs Storage: What Is the Difference?

Memory (RAM) is the fast, temporary workspace a computer uses for the programs and data it is running now, and it is cleared when the power goes off. Storage, such as an SSD or eMMC, keeps the operating system, applications and files permanently. More memory lets a system do more at once; more storage lets it keep more.

6 MIN
STORAGE · ARCHITECTURES

What Is Direct Attached Storage (DAS)?

Direct attached storage (DAS) is storage connected straight to one computer rather than reached over a network. Internal SSDs, drive bays and external enclosures linked by SATA, SAS, NVMe, USB or Thunderbolt are all DAS. It gives low latency and needs no network, but its capacity serves only the host it is connected to.

6 MIN
STORAGE · RELIABILITY

What Is Power Loss Protection in an SSD?

Power loss protection (PLP) is a feature in industrial and enterprise SSDs that keeps data safe if power is cut suddenly. On-board capacitors store enough energy to finish writing any data held in the drive’s cache to its flash memory, so files and the drive’s internal mapping are not corrupted when the supply drops without warning.

6 MIN
STORAGE · M.2 EXPANSION

What is M.2 keying and why does it matter?

M.2 keying is the pattern of notches on an M.2 card and socket that shows which interfaces the slot carries. The four keys in common use are A and E for Wi-Fi and Bluetooth, B for modems and SATA SSDs, and M for NVMe SSDs. A card with the wrong key will not fit the socket.

6 MIN
STORAGE · M.2 SSDS

NVMe vs SATA on M.2 — which should I specify?

NVMe and SATA are two protocols an M.2 SSD can use. NVMe runs over PCIe lanes and typically reads at 3,500 to 7,000 MB/s or more; SATA is capped at 6 Gb/s, around 550 MB/s. Both fit the same M.2 slot shape, so check which protocol the host slot supports. NVMe is the default for new designs.

6 MIN
M.2 EXPANSION · FAQ

What M.2 form factor sizes are available?

M.2 module sizes are written as a code: the first two digits are the width in millimeters and the rest are the length. A 2280 module is 22 mm wide and 80 mm long. The standard defines widths of 12 to 30 mm and lengths of 16 to 110 mm, and 2280 is the most common SSD size.

6 MIN
STORAGE · EXPANSION FORMATS

M.2 vs mSATA vs mPCIe — what’s the difference?

mPCIe (Mini PCIe) is a card format carrying one PCIe lane and USB 2.0. mSATA uses the same card and socket but carries SATA only. M.2 replaced both: it carries up to four PCIe lanes, SATA and USB on one connector, with keying notches that stop the wrong card going in the wrong slot.

7 MIN
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