dmidecode shows details about computer hardware. On RHEL/CentOS, you need to install it with

yum install dmidecode

Show All Hardware Details

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Get RAM Details

dmidecode -t memory

To see installed RAM sizes, run

dmidecode -t memory | egrep "^\s+Size"

Example

[root@server1 ~]# dmidecode -t memory | egrep "^\s+Size"
	Size: 8192 MB
	Size: 8192 MB
	Size: 8192 MB
	Size: 8192 MB
	Size: 8192 MB
	Size: 8192 MB
	Size: 8192 MB
	Size: 8192 MB
	Size: 8192 MB
	Size: 8192 MB
	Size: 8192 MB
	Size: 8192 MB
	Size: 8192 MB
	Size: 8192 MB
	Size: 8192 MB
	Size: 8192 MB
[root@server1 ~]# 

Get system details

dmidecode -t system

Example

[root@server1 ~]# dmidecode -t system
# dmidecode 3.0
Scanning /dev/mem for entry point.
SMBIOS 2.8 present.

Handle 0x001E, DMI type 1, 27 bytes
System Information
	Manufacturer: Huawei
	Product Name: RH2288 V3
	Version: V100R003
	Serial Number: 2102311GGX10GC000072
	UUID: D9919212-BDD1-11E6-8C77-487B6BBEF6B3
	Wake-up Type: Power Switch
	SKU Number: Type1Sku0
	Family: Type1Family

Handle 0x0028, DMI type 32, 20 bytes
System Boot Information
	Status: No errors detected

[root@server1 ~]#