How do I check ram latency?

Question

I need to buy new RAM .

• First I need to know speed >> done
• Second I need to know latency >> how ?

All I tried from google.

dmidecode --type memory
dmidecode 2.11
dd if=/dev/zero of=/dev/sda2 bs=1G count=1 oflag=direct 
apt-get install hardinfo
apt-get install sysinfo
cat /proc/meminfo
cat /var/log/dmesg | grep Memory
decode-dimms
update-pciids
lshw -C memory | grep clock
apt-get install lshw
lshw -C memory

Answer 1

What is Latency ?

A delay in transmitting data between a computer's RAM and its processor. Since RAM is not necessarily fast compared to the computer's processor, RAM latency can occur, causing a delay between the time a computer's hardware recognizes the need for a RAM access (initiates a request for data) and the time the data or instruction is available to the processor. If the CPU requests data that is not stored in the cache, then it will have to wait for the RAM to retrieve the data, opening the door to latency problems.

Where to check Latency of RAM ?

For Ubuntu install package i2c-tools and run

sudo modprobe eeprom
decode-dimms

Source : Ubuntu Forums & Major Source

I hope it will help you.

Answer 2

Please use command 1:

sudo dmidecode -t 17 or dmidecode -t memory

output for command 1:

# dmidecode 2.11
SMBIOS 2.6 present.

Handle 0x000E, DMI type 17, 28 bytes
Memory Device
    Array Handle: 0x000D
    Error Information Handle: No Error
    Total Width: 64 bits
    Data Width: 64 bits
    Size: 2048 MB
    Form Factor: SODIMM
    Set: 1
    Locator: M1
    Bank Locator: Bank 0
    Type: DDR3
    Type Detail: Synchronous
    Speed: 1334 MHz
    Manufacturer: 830B            
    Serial Number: DBC8287D        
    Asset Tag: 1012
    Part Number: NT2GC64B8HC0NS-CG 
    Rank: Unknown
---------------------------------------
output command 2


# dmidecode 2.11
SMBIOS 2.6 present.

Handle 0x000D, DMI type 16, 15 bytes
Physical Memory Array
    Location: System Board Or Motherboard
    Use: System Memory
    Error Correction Type: None
    Maximum Capacity: 16 GB
    Error Information Handle: Not Provided
    Number Of Devices: 4

Handle 0x000E, DMI type 17, 28 bytes
Memory Device
    Array Handle: 0x000D
    Error Information Handle: No Error
    Total Width: 64 bits
    Data Width: 64 bits
    Size: 2048 MB
    Form Factor: SODIMM
    Set: 1
    Locator: M1
    Bank Locator: Bank 0
    Type: DDR3
    Type Detail: Synchronous
    Speed: 1334 MHz
    Manufacturer: 830B            
    Serial Number: DBC8287D        
    Asset Tag: 1012
    Part Number: NT2GC64B8HC0NS-CG 
    Rank: Unknown

Handle 0x000F, DMI type 17, 28 bytes
Memory Device
    Array Handle: 0x000D
    Error Information Handle: No Error
    Total Width: 64 bits
    Data Width: 64 bits
    Size: 4096 MB
    Form Factor: SODIMM
    Set: 1
    Locator: M2
    Bank Locator: Bank 1
    Type: DDR3
    Type Detail: Synchronous
    Speed: 1334 MHz
    Manufacturer: 0198            
    Serial Number: A30EEB39        
    Asset Tag: 1044
    Part Number: 9905428-012.A00LF 
    Rank: Unknown

Handle 0x0010, DMI type 17, 28 bytes
Memory Device
    Array Handle: 0x000D
    Error Information Handle: No Error
    Total Width: Unknown
    Data Width: Unknown
    Size: No Module Installed
    Form Factor: SODIMM
    Set: 1
    Locator: M3
    Bank Locator: Bank 2
    Type: DDR3
    Type Detail: Synchronous
    Speed: Unknown
    Manufacturer:                 
    Serial Number:                 
    Asset Tag:     
    Part Number:                   
    Rank: Unknown

Handle 0x0011, DMI type 17, 28 bytes
Memory Device
    Array Handle: 0x000D
    Error Information Handle: No Error
    Total Width: Unknown
    Data Width: Unknown
    Size: No Module Installed
    Form Factor: SODIMM
    Set: 1
    Locator: M4
    Bank Locator: Bank 3
    Type: DDR3
    Type Detail: Synchronous
    Speed: Unknown
    Manufacturer:                 
    Serial Number:                 
    Asset Tag:     
    Part Number:                   
    Rank: Unknown

Answer 3

On my old Dell Vostro 3700 notebook, with Ubuntu 20.04, 'decode-dimms' worked for me (with 'modprobe eeprom'); it returned a bunch of info like:

Fundamental Memory type                          DDR3 SDRAM
Module Type                                      SO-DIMM
...
Maximum module speed                             1333 MHz (PC3-10600)
...
Minimum Cycle Time (tCK)                         1.500 ns
Minimum CAS Latency Time (tAA)                   13.125 ns

From Crucial site: "latency (ns) = clock cycle time (ns) x number of clock cycles"; so, to find CL class (number of clock cycles), divide "Minimum CAS Latency Time" (latency) by "Minimum Cycle Time" (clock cycle time): the nearest integer should be the CL value (I got 8.75, and CL9 should be consistent with my RAM modules).

Beware: 'decode-dimms' may not output infos on DDR4 systems without finding the correct module needed to read the new SPD Flash memory and it seems to work only on recent Linux releases as wrote Guilherme Parreira above; it may even show you infos about MAXIMUM performances of memory modules, not the actual values they are using. You are warned.

References:

• Crucial - The Difference Between RAM Speed and CAS Latency

• Damieng blog - DDR4 memory information in Linux