Table of contents
DRAM Architecture and Workflow
Memory is a memory device in a computer system, which is used to store programs and various data information. The storage medium of memory mainly uses semiconductor devices and magnetic materials. Next, briefly introduce the main classification of memory.
According to the storage medium, it can be classified into semiconductor memory, magnetic surface memory, and optical memory.
According to the reading and writing function of the memory, it can be classified into read-only memory (ROM) and random read-write memory (RAM).
According to the storability of information, it can be classified into non-permanent memory memory and permanent memory memory.
According to the role in the computer system, it can be classified into main memory (memory), auxiliary memory (external memory), and buffer memory.
According to function/capacity/speed/location, it can be classified into register, cache, internal memory, and external memory.
According to the nature of work/access mode, it can be classified into random access memory, sequential access memory, direct access memory, and associative memory.
ROM and RAM
ROM: Read Only Memory (ReadOnly Memory), non-volatile. It is a solid-state semiconductor memory that can only read data stored in advance. Generally, it is written in advance before loading into the whole machine, and can only be read out during the working process of the whole machine, unlike random access memory, which can be rewritten quickly and conveniently. The data stored in ROM is stable, and the stored data will not change after power off. The ROM in the computer is mainly used to store some system information, or to start the program BIOS program. These are very important. They can only be read and generally cannot be modified, and they will not disappear when the power is turned off.
RAM: Random Access Memory (Random Access Memory), volatile. It is an internal memory that directly exchanges data with the CPU. It can be read and written at any time, and the speed is very fast. It is usually used as a temporary data storage medium for the operating system or other running programs. It is used during the entire program running. The rewritten amount (including global variables, local variables, stack segments, etc.) is stored in RAM. Random access memory is divided into two categories: static and dynamic. Static RAM (SRAM) is faster than dynamic RAM (DRAM), but also much more expensive. SRAM is used as cache memory, either on the CPU chip or off-chip. DRAM is used as the frame buffer of the graphics system.
For example, common hard disks belong to ROM, and memory sticks belong to RAM.
DRAM definition and form
Dynamic Random Access Memory (Dynamic Random Access Memory, DRAM) is a semiconductor memory, the main working principle is to use the amount of charge stored in the capacitor to represent whether a binary bit (bit) is 1 or 0. Due to the phenomenon of leakage current in transistors in reality, the amount of charge stored on the capacitor is not enough to correctly judge the data, resulting in data corruption. Therefore, for DRAM, periodic charging is an unavoidable element. Because of this periodic refresh, it is called "dynamic" memory. Relatively speaking, as long as data is stored in static memory (SRAM), it will not lose memory even if it is not refreshed.
Compared with SRAM, the advantage of DRAM is its simple structure-each bit of data requires only one capacitor and one transistor to process, compared with six transistors usually required for one bit on SRAM. For this reason, DRAM has very high density, high capacity per unit volume and thus low cost. But on the contrary, DRAM also has the disadvantages of slow access speed and high power consumption.
|
|
store information |
destructive readout |
need to refresh |
Send row and column address |
running speed |
Integration |
Calorific value |
storage cost |
| SRAM |
trigger |
no |
no |
at the same time |
quick |
Low |
big |
high |
| DRAM |
capacitance |
yes |
yes |
divided into two |
slow |
high |
Small |
Low |
DRAM storage unit
The DRAM storage unit is a DRAM Storage Cell, and the DRAM Storage Cell is used to store bit information.
DRAM Storage Cell consists of 4 parts:
Storage Capacitor, that is, storage capacitor, which represents logical 0 and 1 by the amount of charge stored in it (or the voltage difference between the two ends of the capacitor);
Access Transistor, that is, the access transistor, its on and off, determines whether to allow or prohibit the reading and rewriting of the information stored in the Storage Capacitor;
Wordline, the word line, which determines whether the Access Transistor is turned on or off;
Bitline, that is, the bit line, is the only channel for the outside world to access the Storage Capacitor. When the Access Transistor is turned on, the outside world can read or write to the Storage Capacitor through the Bitline.
DRAM Architecture and Workflow
1.Command transport and decode
At this stage, the Host will pass the specific Command and corresponding parameters to SDRAM through Command Bus and Address Bus, SDRAM receives and parses the Command, and then drives the internal module to perform corresponding operations.
2.In bank data movement
At this stage, SDRAM mainly reads the data in the Memory Array from DRAM Cells to Sense Amplifiers, or writes data from Sense Amplifiers to DRAM Cells.
3.In device data movement
In this stage, the data will be cached to Read Latches through the IO circuit or updated to Sense Amplifiers through the IO circuit and Write Drivers.
4.System data transport
At this stage, when the data is read, the SDRAM will output the data to the data bus, and when the data is written, the Controller on the Host side will output the data to the bus.