Basic concept of memory

RAM , random access memory, also called main memory, is an internal memory that directly exchanges data with the CPU. It can be read and written at any time (except when refreshing), and it is fast. When RAM is working, information can be written (stored) or read (taken out) from any specified address at any time. The biggest difference between it and ROM is the volatility of data, that is, the stored data will be lost once the power is turned off.
According to different working principles of the storage unit, RAM is divided into static RAM (SRAM) and dynamic RAM (DRAM).

Source: Baidu Encyclopedia - Random Access Memory

ROM , read-only memory, works in a non-destructive read-out mode, and can only read but not write information. Once the information is written, it is fixed, even if the power is cut off, the information will not be lost, so it is also called fixed memory.
From its manufacturing process and function, there are five types of ROM, namely mask-programmed read-only memory MROM (Mask-programmed ROM), programmable read-only memory PROM (Programmable ROM), erasable programmable read-only memory Memory EPROM (Erasable Programmable ROM), electrically erasable programmable read-only memory EEPROM (Elecritically Erasable Programmable ROM) and fast erasable read-write memory (Flash Memory).

Source: Baidu Encyclopedia - Read Only Memory

EEPROM , Electrically Erasable Programmable Read-Only Memory, is a memory that can be written at any time without erasing the original content. Its writing operation takes much longer than the reading operation. EEPROM has the advantages of not easy to lose data and flexible modification Combined, only the normal control, address and data buses are required for modification.

Source: Baidu Encyclopedia - Read Only Memory

Flash Memory , fast erasable read-write memory, using electrically erasable technology, the entire flash memory can be erased within one to several seconds, much faster than EPROM. Also, it can erase certain blocks of memory, rather than the entire chip. Flash memory, however, does not provide byte-level erasure.

Source: Baidu Encyclopedia - Read-only memory

flash card (Flash Card) is a memory that uses flash memory (Flash Memory) technology to store electronic information.
According to different manufacturers and different applications, flash memory cards generally include SmartMedia (SM card), Compact Flash (CF card), MultiMediaCard (MMC card), Secure Digital (SD card), Memory Stick (memory stick), XD-Picture Card (XD card) and micro hard drive (MICRODRIVE). Although these flash memory cards have different appearances and specifications, their technical principles are the same.

Source: Baidu Encyclopedia - Flash Memory

SSD is composed of control unit and storage unit (FLASH chip, DRAM chip).
There are two types of storage media for solid-state drives, one uses flash memory (FLASH chips) as the storage medium, and the other uses DRAM as the storage medium. The latest is Intel's XPoint particle technology.

Baidu Encyclopedia - SSD

Cache , located between the CPU and the main memory DRAM, is a small but high-speed memory, usually composed of SRAM static memory.
Cache is divided into L1Cache (level one cache) and L2Cache (level two cache). L1Cache is mainly integrated inside the CPU, while L2Cache is integrated on the motherboard or on the CPU.

Source: Baidu Encyclopedia - CACHE memory

insert image description here Image source: vivo X90

SDRAM , Synchronous Dynamic Random Access Memory is Dynamic Random Access Memory (DRAM) that has a synchronous interface. Usually DRAM has an asynchronous interface, so that it can respond to changes in the control input at any time. SDRAM, on the other hand, has a synchronous interface that waits for a clock signal before responding to control inputs, so that it can be synchronized with the computer's system bus. The clock is used to drive a finite state machine to perform pipeline operations on incoming instructions.

Source: Baidu Encyclopedia - SDRAM

DDR SDRAM , double rate synchronous dynamic random access memory, people are accustomed to call it DDR. It is SDRAM with double data transfer rate, its data transfer speed is twice the system clock frequency, and its transfer performance is better than traditional SDRAM due to the increased speed. DDR SDRAM can perform data transfer on both the rising and falling edges of the system clock.

Source: Baidu Encyclopedia-ddr

LPDDR , a type of DDR SDRAM, also known as mDDR (Mobile DDR SDRAM), is a communication standard developed by the JEDEC Solid State Technology Association (JEDEC Solid State Technology Association) for low-power memory, with low power consumption and small size Famous, specially used in mobile electronic products.

Source: Baidu Encyclopedia-LPDDR

Registers are composed of flip-flops with storage functions. A flip-flop can store 1-bit binary code, so a register storing n-bit binary code needs to be composed of n flip-flops. Registers have very high read and write speeds.

Source: Baidu Encyclopedia - Register

eMMC is an embedded memory standard specification established by the MMC Association, mainly for products such as mobile phones or tablet computers. Consists of an embedded storage solution with MMC (Multimedia Card) interface, flash memory device and host controller.

Source: Baidu Encyclopedia-eMMC

缩写
RAM：Random Access Memory
ROM：Read-Only Memory
EEPROM：Electrically Erasable Programmable Read-Only Memory
SSD：Solid State Disk或Solid State Drive
DRAM：Dynamic Random Access Memory
SRAM：Static Random Access Memory
SDRAM：Synchronous Dynamic Random Access Memory
DDR：Double Data Rate
LPDDR：Low Power Double Data Rate SDRAM
mDDR：Mobile DDR SDRAM
DMA：Direct Memory Access
eMMC：Embedded Multi Media Card

Basic concept of memory

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