Memory is one of the essential components of a computer, and it is the bridge between External storage and CPU. All programs on a laptop are run in memory, so the performance of consciousness can have a significant impact on the computer. Memory, also known as internal and primary memory, is used to temporarily store computing data in the CPU, as well as data exchanged with External storage such as hard drives. As long as the computer is running, the operating system will transfer the data from memory to the CPU for calculation, and when the count is complete, the CPU will transfer the results, and the memory operation also determines the stable operation of the computer.
Let’s take a look at the types of computer memory, according to different classification methods, the following two types of computer memory are mainly introduced.
Table of Contents
Classification by working principle
- Read-only Memory (ROM)
ROM stands for reading Only memory, where information (data or program) is stored and permanently stored at the time of manufacture. This information can only be read and generally not written, and the data will not be lost even if the machine is powered down.ROMs are typically used to store basic computer programs and data, such as BIOS ROMs.The physical form of the ROM is generally a double in-line plug-in (DIP) integrated block.
The most popular read-only memory is flash memory, which is an upgrade of EEPROM and can be erased repeatedly by electrical principles.
Most BIOS programs are now stored in FlashROM chips. The information stored in the BIOS controls the operation of your computer system. Because of its importance, unauthorized copying or deletion of the BIOS is not allowed. However, there are some different general types of ROMs, which can refresh their content for a particular requirement.
(1) ROM – This is a standard ROM for permanently storing important data. When a technological product requires that some of its information does not change with external factors, they usually use this standard ROM module. In a ROM, the information is permanently etched into the ROM unit, which makes it impossible to change the information in the ROM after the etching is complete.
(2) PROM (Programmable ROM) – This type of ROM works similar to CD-R in that it allows you to rewrite the data in it all at once, remember: rewrite the data only once. Once the information is written to the PROM, the data is permanently etched into it, and the PROM is no different from the ROM described above.
(3) EPROM (Erasable Programmable ROM) – Of course, if the data stored in the ROM needs to be erased or rewritten, EPROM can do it. Using UV exposure to this type of ROM can erase the data in it, and it also allows the information you need to be stored in such a ROM.
(4) EEPROM (Electrically Erasable Programmable ROM) – This type of ROM is now commonly used in the BIOS of computer systems and is very similar to EPROM. As the name suggests, for this EEPROM, we can use electricity to erase it without UV light, which is very useful for the BIOS of the motherboard. Based on the principle described above, motherboard manufacturers can release their latest BIOS for users to upgrade their motherboard’s BIOS, and the way to upgrade is to use the BIOS upgrade program to generate electrical signals to trick the information in the new BIOS.
From the above analysis, it is clear that not all ROM memory is “Read Only,” you may wonder why they are called Read Only. In fact, this is just an extension of the historical name; as for the non-read-only part, but brings us a lot of good; for example, EEPROM is often used in the motherboard BIOS, because it is not read-only, but erasable so that the motherboard manufacturer can release the latest motherboard BIOS upgrade programs, users need to download and run these programs to upgrade the motherboard BIOS, instead of taking the motherboard to the manufacturer to upgrade the BIOS.
- Random storage (RAM)
Random Access Memory means that data can be read or written from it. When the machine is powered off, the data stored in it is lost. The memory strips we usually buy or upgrade are random memory, and memory strips are small boards that hold RAM integration blocks together, which are plugged into memory slots in the computer to reduce the amount of space the RAM integration blocks take up. The common memory strips on the market today are 2G/bar, 4G/bar, 8G/bar, etc.
DRAM (Dynamic RAM, Dynamic Random Memory) is made of capacitors and related components; the amount of charge stored in the capacitor represents signals 0 and 1.
SRAM (Static RAM, Static Random Memory) memory cells are latches made of transistors and associated components, each with a function to latch “0” and “1” signals. It is fast and does not require refresh operation, but has poor integration and high power consumption, and is typically used to manufacture small capacity but efficient CPU caches.
- Cache
The cache is also a concept that we often encounter, which is the data that we usually see as first-level cache (L1 Cache), second-level cache (L2 Cache), third level cache (L3 Cache), which is located between the CPU and Memory, a memory that reads and writes faster than a memory. When the CPU writes or reads data into memory, this data is also stored in cache memory. When the CPU needs this data again, the CPU reads the data from the cache instead of accessing the slower memory, of course, if the data needed is not available in the cache, the CPU will reread the data in memory.
Classification by technical memory standard
1.SDRAM
(Synchronous Dynamic RAM, synchronous dynamic random memory) using 3.3V operating voltage, memory data bits wide 64-bit. SDRAM and CPU are locked together by an identical clock frequency, allowing both to work at the same speed. SDRAM It transfers data along the rising edge of each clock pulse to the 168 feet of the SDRAM memory gold finger.
SDRAM memory is available in the following types: PC66/100/133150/166 with core frequencies of 66MHz, 100Mz133MHz, 150MHz, 166MHz. clock frequency, equivalent frequency, and core frequency equal to a single SDRAM memory data transfer bandwidth of up to 166MHz × 64bit ÷ 8 = 1.3GB/s.
Related concepts
Core frequency: is the operating frequency of the internal memory cell of the memory particle, i.e., the refresh frequency of the capacitor. It is the base frequency on which the memory works, and all other frequencies are built on it.
Clock frequency: also known as memory bus frequency, is the operating frequency of the motherboard clock chip to provide memory.
Equal frequency: also known as the equivalent data transmission frequency, is the actual frequency of memory and external data exchange. Usually, what is labeled on memory is equivalent efficiency.
2.DDR SDRAM
(Double Data Rate SDRAM, Double Rate Synchronous Dynamic Random Memory) uses 2.5V operating voltage and 64-bit wide memory data bits. DDR SDRAM (abbreviated as DDR memory) A clock pulse transmits data twice, once on each of the rising and falling edges of the clock pulse, and is therefore called double-rate SDRAM.
The DDR memory gold finger is 184 feet.DDR memory has the following: DDR 200 / 266 / 333400 / 500.The core frequency is equal to the clock frequency, 100 MHz, 133 MHz, 166 MHz, 200 MHz, 250 MHz, and the equivalent frequency is 200 MHz, 266 MHz, 333 MHz, 400 MHz, 500 MHz, please note that the equivalent frequency of DDR memory is twice the clock frequency, because DDR memory works at double rate.DDR memory core uses 2-bit data pre-reading, that is, taking 2 bits at a time (one pulse).
The DDR memory core frequency is equal to the clock frequency, and the equivalent frequency is twice the clock frequency, so the number of memory cores taken out at one time (one pulse) can be transferred out at one time (one pulse) in a timely manner. Single DDR memory data transfer bandwidth is up to 500 MHz x 64 bit 8-4 GB/s.
3.DDR2 SDRAM
(Double Data Rate 2 SDRAM) uses 1.8V operating voltage and 64-bit wide memory data. Like DDR memory, DDR2 Memory transmits data twice in a single clock pulse, but DDR2 memory has twice the pre-reading capability of the previous generation of DDR memory, i.e., 4-bit data pre-reading.
The DDR2 memory has the following types: DDR2 533 / 667 / 800 / 1066. core frequencies are 133 MHz, 166 MHz, 200 MHz, 266 MHz, clock frequencies are: 266 MHz, 333 MHz, 400 MHz, 533 MHz, equivalent frequencies are 533 MHz, 667 MHz, 800 MHz, 1066 MHz. [4]
As mentioned before, DDR2 memory core uses 4-bit data pre-reading, that is, 4 bits at a time (one pulse), if, like the previous generation of DDR memory, the clock frequency is equal to the core frequency, and the equivalent frequency is twice the clock frequency, it will not be able to transfer the number taken out in time; therefore, the clock frequency of DDR2 memory is twice the core frequency, so that the number taken out from the memory core in the same time interval can be transferred out in the same interval.
The data transfer bandwidth for a single DDR2 memory is up to 1066 MH2z X 64 bit 8 – 8.6 GB/s.
4.DDR3 SDRAM
(Double Data Rate 3 SDRAM) uses 1.5 V operating voltage and 64-bit wide memory data. Likewise, DDR3 Memory has twice the pre-reading power of the previous generation DDR2 memory, i.e., 8-bit data pre-reading.
For DDR3 memory, the following relationship can be derived: the clock frequency is four times the core frequency, and the equivalent frequency is two times the clock frequency, which means that the DDR3 memory equivalent frequency is eight times the core frequency.
DDR3 memory has the following types: DDR3 1066 / 1333 / 1600 / 1800 / 2000. core frequencies are 133 MHz, 166 MHz, 200 MHz, 225 MHz, 250 MHz, clock frequencies are 533 MHz, 667 MHz, 800 MHz, 900 MHz, 1000 MHz, equivalent frequencies are 1066 MHz, 1333 MHz, 1600 MHz, 1800 MHz, 2000 MHz. data transfer bandwidth of a single DDR3 memory is up to 2000 MHz × 64 bit÷ 8 -16 GB/s.
5.DDR4 SDRAM
(Double Data Rate 4 SDRAM) uses 1.2V operating voltage, 64-bit wide memory data, 16-bit data pre-reading. Eliminate the two-channel mechanism, and one memory is one channel. The operating frequency is up to 4266 MHz, and the data transfer bandwidth is up to 34 GB/s for a single DDR4 memory.