Random-access memory
Random-access memory (RAM) is the system memory used to run software and temporarily store data and cache of more permanent storage-technologies like Solid State Drives and hard drives. The contents of the systems RAM disappear after a minute when power is turned off. It is generally a lot faster than permanent storage solutions.
HOWTO do a close-up inspection of your RAM[edit]
The handy tool dmidecode - found in a package with that name - can be used to inspect all kinds of incriminating information about a computer, including the RAM amount and type. It must be executed as root since it requests information from /sys/firmware/dmi and /dev/mem. The option -t memory will limits it's output to memory-related information:
dmidecode -t memory
This command will produce a summary of memory followed by details about each stick. The summary looks like this:
Handle 0x0027, DMI type 16, 23 bytes
Physical Memory Array
Location: System Board Or Motherboard
Use: System Memory
Error Correction Type: None
Maximum Capacity: 256 GB
Error Information Handle: 0x0026
Number Of Devices: 4
This will be followed by one, two or four or more listings - one for each memory stick - like this:
Handle 0x0037, DMI type 17, 40 bytes
Memory Device
Array Handle: 0x0027
Error Information Handle: 0x0036
Total Width: 64 bits
Data Width: 64 bits
Size: 8192 MB
Form Factor: DIMM
Set: None
Locator: DIMM 1
Bank Locator: P0 CHANNEL B
Type: DDR4
Type Detail: Synchronous Unbuffered (Unregistered)
Speed: 2666 MT/s
Manufacturer: Unknown
Serial Number: 00000000
Asset Tag: Not Specified
Part Number: CMK32GX4M4A2666C16
Rank: 1
Configured Memory Speed: 2666 MT/s
Minimum Voltage: 1.2 V
Maximum Voltage: 1.2 V
Configured Voltage: 1.2 V
It is obviously possible to pipe the output to grep to get limited information like the memory's speed when setting up a new system:
dmidecode -t memory|grep Speed
Getting amount of total and used memory[edit]
The command free will show this information. It will look like this:
total used free shared buff/cache available Mem: 32913316 11395368 1357032 916988 20160916 19422248 Swap: 20971516 338688 20632828
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Note: The number shown as available is the number in free's output which actually refers to how much memory applications are free to use. Linux will by default cache anything because using caches are always much faster than direct IO. The number shown as "free" means unused while used refers to what applications are using - which may be somewhat confusing because "used"+"buff/cache" is the actual amount of memory the Linux kernel is using for something. However, the amount used for "buff/cache" will be dropped as soon as any applications requests more memory than what is "free".
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