[immortality]

why cpu Mhz is shown 1400 by using lscpu command?
while it should be 4200Mhz!

ehsan@Ehsan-com:~$ lscpu
Architecture:          x86_64
CPU op-mode(s):        32-bit, 64-bit
Byte Order:            Little Endian
CPU(s):                4
On-line CPU(s) list:   0-3
Thread(s) per core:    2
Core(s) per socket:    2
CPU socket(s):         1
NUMA node(s):          1
Vendor ID:             AuthenticAMD
CPU family:            21
Model:                 1
Stepping:              2
CPU MHz:               1400.000
BogoMIPS:              8399.94
Virtualization:        AMD-V
L1d cache:             16K
L1i cache:             64K
L2 cache:              2048K
L3 cache:              8192K
NUMA node0 CPU(s):     0-3

[CapSizer]

Give the machine something to do. It clocks itself down to save energy when it is idle. In fact, it clocks up its cores selectively when it is running, as per requirement.

[immortality]

thanks.now its 4200.then it shows frequency in real time not the maximum frequency can reached.

ehsan@Ehsan-com:~$ lscpu
Architecture:          x86_64
CPU op-mode(s):        32-bit, 64-bit
Byte Order:            Little Endian
CPU(s):                4
On-line CPU(s) list:   0-3
Thread(s) per core:    2
Core(s) per socket:    2
CPU socket(s):         1
NUMA node(s):          1
Vendor ID:             AuthenticAMD
CPU family:            21
Model:                 1
Stepping:              2
CPU MHz:               4200.000
BogoMIPS:              8399.94
Virtualization:        AMD-V
L1d cache:             16K
L1i cache:             64K
L2 cache:              2048K
L3 cache:              8192K
NUMA node0 CPU(s):     0-3

[wyldckat]

There are two situations here in play:

1. Originally Posted by http://en.wikipedia.org/wiki/Phenom_II

   "Thuban" and "Zosma" Phenom II processors support AMD's Turbo Core overclocking performance-boost technology. When not all cores are needed, the processor will automatically overclock up to half of the cores by up to 500 MHz, leaving the other half idle. In turn, when the application demands more than half of the cores, the processor will run on standard clock rate and with all cores enabled.[10]

   This means that 4.4GHz can only be reached if you're using only 2 cores.
2. The other situation is that, at least with Intel processors, the Linux kernel is not very able to figure out the actual speed of the processor. I've seen this several times on machines that have serious overclock in them, but the kernel only sees the maximum stock speed.