(1) Memory
Memory is a memory device used to store information in modern information technology. Its concept is very broad and has many levels. In a digital system, as long as it can store binary data, it can be a memory; in an integrated circuit, a circuit with a storage function without physical form is also called a memory, such as RAM, FIFO, etc.; In the system, the storage device with physical form is also called memory, such as memory stick, TF card, etc. All the information in the computer, including the input original data, the computer program, the intermediate running results and the final running results are stored in the memory. It stores and retrieves information according to the location specified by the controller . With memory, the computer has the memory function to ensure normal work. The memory in the computer can be divided into main memory (memory) and auxiliary memory (external memory) according to the purpose, and there are also classification methods for external memory and internal memory. External storage is usually a magnetic medium or an optical disc, etc., which can store information for a long time. Memory refers to the storage components on the motherboard, which are used to store the data and programs currently being executed, but are only used to temporarily store programs and data. When the power is turned off or powered off, the data will be lost.
The classification structure of memory is as follows:
( 2) RAM
Random access memory (random access memory, RAM), also known as " random access memory ", is an internal memory that directly exchanges data with the CPU , also known as main memory (memory). It can be read and written at any time, is fast, and is often used as a temporary data storage medium for the operating system or other running programs.
SRAM ：
(3) ROM
Read-Only Memory (Read-Only Memory) is a memory that can only read data. In the manufacturing process, the data is programmed into the circuit with a special mask, and the content of the data cannot be changed after being written, so it is sometimes called "mask ROM". This memory is cheap to manufacture and is often used for booting up in computers.
1.PROM
The programmable read-only memory (Programmable ROM, PROM) has a determinant filament inside, which can be blown by current as needed, and the required data can be written, but it can only be written once. When the PROM leaves the factory, the stored content is all 1, and the user can write data 0 to some of the units as needed (part of the PROM leaves the factory with all 0 data, then the user can write 1 to some of the units) , for the purpose of "programming" it. The typical product of PROM is "bipolar fuse structure". If we want to rewrite some cells, we can pass a large enough current to these cells and maintain it for a certain period of time, and the original fuse can be blown, so that the The effect of overwriting some bits is achieved. Another type of classic PROM is the PROM that uses "Schottky diode". When leaving the factory, the diode is in the reverse cut-off state, and the reverse voltage is applied to the "Schottky diode" by means of a large current, causing its A permanent breakdown is sufficient.
2.EPROM
Erasable Programmable Read Only Memory (EPROM) can use high voltage to program and write data. When erasing, exposing the circuit to ultraviolet light, the data can be cleared and reused. Usually, a quartz transparent window is reserved on the package casing to facilitate exposure. 3OTPROM
The writing principle of One Time Programmable Read Only Memory (OPTROM) is the same as that of EPROM, but in order to save cost, it will not be erased after programming and writing, so no transparent window is set.
4.EEPROM
Electronically Erasable Programmable Read Only Memory (EEPROM) operates similarly to EPROM, but the erasing method is done using a high electric field, so a transparent window is not required.
5. Flash memory
Each memory cell of the flash memory (Flash memory) has a "control gate" and a "floating gate", which can be programmed by changing the threshold voltage of the floating gate with a high electric field.
6. Flash memory
Refers to the main game file extracted from the main file storage of the game console or the genuine game cartridge, which can be used on various emulators. For example, arcade emulators, ROMs for GBA emulators, are exactly that.
(4) External memory
1 hard drive
The hard disk is one of the main storage media of the computer and consists of one or more aluminum or glass discs. The disc is covered with ferromagnetic material.
Hard disks include solid-state hard disks (SSD disks, new hard disks), mechanical hard disks (HDD traditional hard disks), and hybrid hard disks (HHD is a new hard disk based on traditional mechanical hard disks).
SSD uses flash memory particles for storage, HDD uses magnetic discs for storage, and hybrid hard disk (HHD: Hybrid Hard Disk) is a kind of hard disk that integrates magnetic hard disk and flash memory. The vast majority of hard drives are fixed hard drives that are permanently sealed in the hard drive.
2 floppy disks
Floppy Disk is the earliest removable medium used in personal computers (PCs). Reading and writing to a floppy disk is done through the floppy disk drive. Floppy disk drives are designed to accept removable floppy disks, the most commonly used today being 3.5-inch floppy disks with a capacity of 1.44MB.
The floppy disk has a slow access speed and a small capacity, but it is removable and easy to carry. As a removable storage method, it is ideal for small files that need to be physically moved.
A floppy disk was a necessary piece of hardware on early computers, and it was also the earliest removable medium used on computers. The English abbreviation of floppy disk is FIoppy Disk, which as a removable storage hardware is suitable for some small files that need to be physically moved.
3 discs
An optical disc is an object that uses optical information as a storage carrier and is used to store data. Non-rewritable optical discs, such as CD-ROM, DVD-ROM, etc.; and rewritable optical discs, such as CD-RW, DVD-RAM, etc.
Optical disc is a device that uses laser principle to read and write. It is a rapidly developing auxiliary memory, which can store various multimedia digital information such as text, sound, graphics, images and animations.
Definition of optical disc: that is, a compact disc is an optical storage medium developed in modern times that is different from a complete magnetic carrier (for example, a magneto-optical disc is also an optical disc), which uses a focused hydrogen ion laser beam to process the recording medium. Also known as laser disc.
4 U disk
U disk, full name USB flash disk, English name "USB flash disk". [1] It is a miniature high-capacity mobile storage product that uses a USB interface and does not require a physical drive. It is connected to a computer through a USB interface to achieve plug-and-play. [1]The name of U-disk originated from a new type of storage device produced by Netac Technology, called "U-disk", which uses a USB interface for connection. After the U disk is connected to the USB interface of the computer, the data of the U disk can be exchanged with the computer. And the equipment with similar technology produced after that can no longer be called "USB flash drive" because Netac has already registered the patent, but changed to "USB flash drive" with homophonic sound. [1] Later, the name U disk is widely known because of its simplicity and easy to remember, and it is one of the mobile storage devices. Now there are many U disks that support multiple ports on the market, namely three-way U disk (USB computer port, iOS Apple interface, Android interface).
(5) Cache
The cache is the buffer (called Cache) for data exchange. When a certain hardware wants to read data, it will first look for the required data from the cache. If it is found, it will be executed directly, and if it cannot be found, it will be found in memory. Since the cache runs much faster than the memory, the purpose of the cache is to help the hardware run faster.
Because the cache often uses RAM (non-permanent storage that is lost when power is off), the file will still be sent to the hard disk and other storage for permanent storage after it is used up. The largest cache in the computer is the memory stick. The fastest is the L1 and L2 caches embedded on the CPU. The video memory of the graphics card is the cache for the graphics card computing chip. There are also 16M or 32M caches on the hard disk.