Level 2 - RAM hardware, storage devices, RAID

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What is RAM?

Random Access Memory

Data is stored on hard drives or SSD

Data must be moved to RAM in order to execute

Speed is most important

Must be compatible with motherboard

DIMM / SO-DIMM

Dual inline memory module

DIMM - 64 bit data width

SO-DIMM - 32 bit data width, for laptops and mobile

DRAM

Dynamic Random Access Memory

The memory stored on DIMM

Dynamic - needs constant refreshing, or else data disappears

Random access - any storage location can be accessed directly

SDRAM

Synchronous DRAM - synced with system clock

Queue up a process while waiting for another

More modern

DDR3 SDRAM

2x data rate of regular SDRAM

Max 16 GB per DIMM

Not backwards compatible

DDR4 SDRAM

Even faster

64 GB per DIMM

Not backwards compatible

DDR5

EVEN FASTER

Max 64 GB per DIMM

Not backwards compatible

Virtual memory

Memory technology

Swap unused application data to storage, which frees space for other apps

Managed automatically by OS

Multi-channel memory

Memory technology

Dual, triple, or quad channel memory

Memory that checks itself

Memory Technology

Used on critical systems - VM servers, database servers, any server

Parity memory - cannot correct errors, will sometimes detect errors

Error Correcting Code (ECC) - detect and correct errors

Hard disk drives (HDD)

Non-volatile magnetic storage

Are random access, can retrieve data from any part of the drive at any time

Moving parts are limited in speed and can break

Solid state drive (SSD)

Non-volatile memory

No moving parts

Very fast, no spinning delay

Mini-SATA (mSATA)

Shrink SATA drives for smaller devices (laptop / mobile)

Smaller than 2.5 inch SATA drive

Quickly replaced by M.2

^SATA

For hard drives

Uses Advanced host controller interface (AHCI) to move data to RAM

SATA version 3 up t o600 MB/s

SSDs need faster communication

NVMe

Non-volatile memory express

Designed for SSD, lower latency, higher throughput

M.2 Interface

M.2 does not guarantee NVMe, M.2 may use AHCI

M.2 uses smaller form factor - No SATA or power cables

Can use PCI Express bus connection at 4GB/s or faster using NVMe

Uses different connector types (B key, M key, B and M, depends on motherboard)

Flash drives

Flash memory can be non volatile (no power needed to retain data) or EEPROM (electrically erasable programmable read-only memory)

Limited number of writes, but always readable

Not designed for archive storage - easily lost or damaged

Optical drive

Small bumps are read by a laser beam, microscopic binary storage

Ex: CD-ROM, DVD-ROM, Blu-ray

Present as internal and external drives

Data redundancy

Hard drives eventually break or fail

RAID is NOT backup

RAID 0 - Striping

Data split across 2 or more drives

0 redundancy

high performance, data written quickly

RAID 1 - Mirroring

File blocks duplicated between 2 or more drives

High disk utilization, required double disk space

High redundancy

Failure does not affect data availability

RAID 5 - Striping with Parity

Minimum 3 disks

Parity block present in all disks, allows data to be rebuilt

Can withstand failure of one drive without data loss

RAID 10 - Stripe of mirror

Minimum 4 disks

File blocks are mirrored, then striped

Can tolerate failure of one drive for each pair without data loss

High utilization, need double disk space