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  1. In Lubuntu 18.04 in a laptop (Model Name: SATELLITE C55DT-A5244), free shows its RAM ram is 3.3G

    $ free -h
              total        used        free      shared  buff/cache   available
Mem:           3.3G        1.2G        444M         46M        1.7G        1.8G

    while lshw shows the RAM should be 4GiB

     *-memory
      description: System Memory
      physical id: d
      slot: System board or motherboard
      size: 4GiB
    *-bank:0
         description: SODIMM DDR3 Synchronous Unbuffered (Unregistered) 533 MHz (1.9 ns)
         product: M471B5673FH0-CF8
         vendor: Samsung
         physical id: 0
         serial:  
         slot: DIMM 0
         size: 2GiB
         width: 64 bits
         clock: 533MHz (1.9ns)
    *-bank:1
         description: SODIMM DDR3 Synchronous Unbuffered (Unregistered) 800 MHz (1.2 ns)
         product: M471B5773CHS-CK0
         vendor: Samsung
         physical id: 1
         serial: 
         slot: DIMM 1
         size: 2GiB
         width: 64 bits
         clock: 800MHz (1.2ns)

    Why do the 3.3G and 4GiB differ? The difference between 4GiB i.e. 4.29497 GB, and 3.3G is 0.99GB, i.e. 990MB.

    The two RAM chips have different frequencies: 533MHz and 800MHz. Can that be a problem? What frequencies should the two RAM chips be?

  2. In another Thinkpad T400 laptop, under Lubuntu 18.04, free and lshw also don't report the same RAM size, though with difference smaller than the previous laptop: free shows 7.7G RAM, and lshw shows 8GiB RAM from two RAM chips of the same frequency. The difference between 8GiB i.e. 8.58993 GB, and 7.7G is 0.89GB, i.e. 890MB.

     *-memory
      description: System Memory
      physical id: 2b
      slot: System board or motherboard
      size: 8GiB
    *-bank:0
         description: SODIMM DDR3 Synchronous 1066 MHz (0.9 ns)
         product: SUPERTALENT02
         vendor: 8634
         physical id: 0
         serial: 00000000
         slot: DIMM 1
         size: 4GiB
         width: 64 bits
         clock: 1066MHz (0.9ns)
    *-bank:1
         description: SODIMM DDR3 Synchronous 1066 MHz (0.9 ns)
         product: SUPERTALENT02
         vendor: 8634
         physical id: 1
         serial: 00000000
         slot: DIMM 2
         size: 4GiB
         width: 64 bits
         clock: 1066MHz (0.9ns)

Thanks.

Tim
  • 26,107

1 Answers1

5

In both cases, the difference is probably the amount of system RAM that's shared to the built-in graphics adapter. There is also some amount of RAM taken by the OS that doesn't show (it's usually a small amount, and varies depending on a number of factors, including kernel version and compiled-in drivers). This RAM isn't shown by free because it's not available for the OS to use at any time, but lshw is examining the hardware information, not the BIOS/OS reported RAM figures.

Zeiss Ikon
  • 5,248