What is computer memory?

Computer memory is a data storage technology that is capable of storing or saving data, temporarily or permanently. The data stored are in a binary form such as 0 and 1 as well, allowing the user to save and retrieve the information anytime they require it.

What is internal memory and how is it different from external memory?

Computer memory is generally classified as either internal or external memory.

Internal memory, also called “main or primary memory” refers to memory that stores small amounts of data that can be accessed quickly while the computer is running.

External memory, also called “secondary memory” refers to a storage device that can retain or store data persistently. They could be embedded or removable storage devices. Examples include hard disk or solid state drives, USB flash drives, and compact discs.

Primary Memory

ROM: MROM, PROM, EPROM, EEPROM

RAM: SRAM, DRAM

Secondary Memory

SDD: SATA, PCIe, M.2, U.2, NVMe
HDD
Flash Drives
NAS
SAN
Cloud Storage (tertiary memory)

Difference Between RAM and ROM

Read Only Memory (ROM) 

Stores crucial information essential to operate the system, like the program essential to boot the computer.
It is not volatile.
Always retains its data.
Used in embedded systems or where the programming needs no change.
Used in calculators and peripheral devices.
ROM is further classified into 4 types- ROM, PROM, EPROM, and EEPROM.

What are the types of ROM?

PROM (Programmable read-only memory) – It can be programmed by user. Once programmed, the data and instructions in it cannot be changed.

EPROM (Erasable Programmable read only memory) – It can be reprogrammed. To erase data from it, expose it to ultra violet light. To reprogram it, erase all the previous data.

EEPROM (Electrically erasable programmable read only memory) – The data can be erased by applying electric field, no need of ultra violet light. We can erase only portions of the chip.

MROM (Marked ROM) – The very first ROMs were hard-wired devices that contained a pre-programmed set of data or instructions. These kind of ROMs are known as masked ROMs, which are inexpensive.

Random Access Memory (RAM)

It is also called as read write memory or the main memory or the primary memory.
The programs and data that the CPU requires during execution of a program are stored in this memory.

It is a volatile memory as the data loses when the power is turned off.
RAM is further classified into two types- SRAM (Static Random Access Memory) and DRAM (Dynamic Random Access Memory).

What are the types of RAM?

SRAM (pronounced ES-RAM) is made up of four to six transistors. It keeps data in the memory as long as power is supplied to the system unlike DRAM, which has to be refreshed periodically. As such, SRAM is faster but also more expensive, making DRAM the more prevalent memory in computer systems.

DRAM (pronounced DEE-RAM), is widely used as a computer’s main memory. Each DRAM memory cell is made up of a transistor and a capacitor within an integrated circuit, and a data bit is stored in the capacitor. Since transistors always leak a small amount, the capacitors will slowly discharge, causing information stored in it to drain; hence, DRAM has to be refreshed (given a new electronic charge) every few milliseconds to retain data.

What is the Secondary Memory?

The secondary memory is also known as external memory or auxiliary memory. Unlike primary memory, secondary memory is generally volatile and they tend to process data slower than primary memory. The secondary is comparably less important than primary memory since they’re basically extra storage for more data.

SSD: Solid-State Drive

SSD uses a simple memory chip called NAND flash memory, and it is a newer kind of storage devices used in computers, meant to replace HDDs (we’ll address this later). SSDs are able to speed up your computer which could improve the overall performance.

SATA: Serial Advanced Technology Attachment

SATA SSDs are pretty common and they are a type of interface connection that allows SSDs to communicate data with the system. You can basically use SATA with any laptop or computer, even if its a very old one.

PCIe: Peripheral Component Interconnect Express

PCIe, also abbreviated as PCI Express, is a solid-state drive connected to a computer system using a PCIe interface. Since it is plugged into the sever’s backplane, it is able to integrate flash directly on the sever’s motherboard which greatly improves the transfer speed. This also makes PCIe the fastest SSD when compared to the rest.

M.2

M.2 SSD was previously known as NGFF (Next Generation Form Factor), which contains flash memory and controller chips. You might have already realised it, but M.2 look rather similar to RAM, though it is much smaller and is a standard in ultrabooks or tablet computers!

U.2

U.2 SSD is previously known as SFF-8639, an interface that is defined as SSD Form Factor Working Group (SFFWG). It is similar to M.2, which utilises PCIe interface to send data. It is versatile and compatible with SATA, SATA-E, PCIe etc.

NVMe

NVM Express or NVMe is short for Non-Volatile Memory Host Controller Interface Specification (NVMHCIS). It is basically attached to a PCIe slot on the mainboard, which reduces I/O overhead and helps to improve the disk’s performance. This includes multiple long command queues and reduced latency.

HDD: Hard Disk Drive

HDD is a traditional storage device, also known as magnetic storage devices, where the data is stored using a magnetized medium. These devices usually have very large capacities and they’re pretty affordable too!

Flash Drives

Flash drives are also known as thumb drives, pen drives and sometimes USB drives, it is also one of the most popular secondary storage devices. They are basically a small portable storage device that allows you to store, rewrite, and delete data easily.

NAS: Network-Attached Storage

NAS is a type of storage network, it is basically a specialised file server. What’s great about NAS is that it has a ton of space and as long as you have an ethernet connection, you’ll be able to gain access.

SAN: Storage Area Network

SAN is also another type of storage network, similar to NAS, SAN takes storage devices away from the server to create a central pool of data. However, SAN is not dependant on Local Area Network (LAN), the capacity is pooled and provided a dedicated network.

Tertiary Memory: Cloud Storage

Cloud storage or clouding as some may refer it, is relatively common these days and it is basically a collection of networked computer hardware that provides the many aspects of computing in the form of online services.

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