Linux System free Command detailed

       Total used       free     shared    buffers     cachedmem:        8061128     3604036    4457092        324     191296    2283328-/+ Buffers/cache:    1129412    6931716Swap:            0          0           0

Above is the result of the free command, let me explain in detail the meaning of it:

Mem

Total: This is the amount of physical memory, which is the size of the physical memory.

Used: Represents the amount that the total is allocated to the cache (including buffers and cache), but may not be actually used in some of the caches.

Free: Memory that has not been allocated.

GKFX: shared Memory, general system will not be used, nor discussed here.

Buffers: The number of buffers that are allocated but not used by the system.

Cached: The number of caches that the system allocates but has not been used.

-/+ buffers/cached: Represents the cache statistics for physical memory.

Used: The used–buffers-cached in the first row is also the amount of memory actually used.

Free: unused buffers with cache and unallocated memory, buffers1 + cached1 + free1, which is the actual available memory for the system.

The second line of Used+free is the total of the first row.

Expand reading:

ROM

Read only memory abbreviation, Chinese name is Read Only .

In the case of a power outage, the data is not lost and is typically used to store fixed software and information. For example, the BIOS on the motherboard is ROM.

RAM

The abbreviation for random Access memory, the Chinese name is the memory of RAM, short Read and write memory .

In the case of a power outage, all of the data is lost and is typically used to store temporary data. The memory of the computer is RAM.

RAM is divided into two main categories:

static RAM (SRAM)

SRAM read and write speed is very fast, of course, the price is very expensive, generally used for the CPU level, level two cache.

dynamic RAM (DRAM)

DRAM performance is lower than SRAM, but much stronger than ROM, the price is appropriate, the general calculation of memory is DRAM.

DRAM is also divided into a variety of different types, here is the most common kind of DDR RAM.

double date-rate synchronous ram abbreviation, Chinese name is double rate synchronous dynamic RAM.

DDR RAM can read and write data two times on a single clock, which doubles the data transfer speed. can go online to see, now computer memory is not DDR3 is DDR4.

How the Memory works

Memory is used to store data and programs that are currently in use (that is, in progress), the memory of the computer we refer to is dynamic memory (that is, DRAM), the so-called "dynamic" in dynamic memory, that is, when we write data to DRAM, the data is lost after a period of time, Therefore, an additional device is required for a memory refresh operation.

The specific work process is this:

A DRAM storage unit is 0 or 1 depending on whether the capacitor has an electric charge, an electric charge represents 1, and no charge represents 0. But a long time, representing 1 of the capacitance will discharge, representing 0 of the capacitance will absorb the charge, this is the reason for the loss of data; The refresh operation periodically checks the capacitance, if the charge is greater than 1/2 of the charge, it is considered to represent 1, and the capacitance is fully charged, if the charge is less than 1/2, it is considered to represent 0 To maintain the continuity of the data.

Linux System free Command detailed