I ask for my friend : The Sterlincoin Client is using 20-30% of my cpu very often. how can I reduce this?
Sorry your friend is having this frustration. Without knowing more, I will assume you are asking about a Windows Sterlingcoin Client and better and/or dedicated hardware is not an option.
Your friend could stake less-often. This can be done by encrypting your Sterlingcoin wallet.dat, thereby making it locked by default, and only unlock it once a week or once a month. Though you will, as always, experience high cpu usage during network sync. If you opt to stake less-frequently, you may want to leave your wallet locked to remain in sync.
Conversely, you could stake less-often by enabling and disabling staking via "staking=1" (true) or "staking=0" (false) added to your sterlingcoin.conf file. This option works for both encrypted and un-encrypted wallets. That file would be located withing your Sterlingcoin data directory which, on Windows, is C:\Users\[your Windows username here]\AppData\Roaming\sterlingcoin or just %appdata%/sterlingcoin/
So long as you stake for several hours, long enough to stake a block once or more a month, your PoS reward will be 5.5% annual. Though more often is appreciated because your computational contribution does help the Sterlingcoin network. Running a synced node, even when not staking, does also help the network, but to a lesser-degree. Both are appreciated.
If your friend has a 64-bit cpu, they will be happy to learn a 64-bit-specific build is expected the next release. There is no firm ETA of that as of this moment, but do expect one in the near future.
To you and your friend, thanks for supporting Sterlingcoin.