Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!apple!agate!usenet.ins.cwru.edu!gatech!utkcs2!usenet From: wnn@ornl.gov Newsgroups: comp.sys.mac.hardware Subject: Re: Leaving the Mac on Message-ID: <1991Feb27.225011.6594@cs.utk.edu> Date: 27 Feb 91 22:50:11 GMT References: <9262.27c24f4a@cc.newcastle.edu.au> <39523@cup.portal.com> Sender: usenet@cs.utk.edu (USENET News Poster) Organization: University of Tennessee/Oak Ridge National Labora Lines: 36 In article hamilton@kickapoo.cs.iastate.edu (Jon Hamilton) writes: >yee@osf.org (Michael K. Yee) writes: > >>In article hamilton@kickapoo.cs.iastate.edu (Jon Hamilton) writes: >>> John_Richard_Bruni@cup.portal.com writes: > > >> I like to know how MTBF (mean time between failure) is INCREASED by >> leaving a hard drive on? Isn't MTBF expressed in hours? So it >> should follow that the less time you have the drive on, the longer >> it should last, right? What am I missing here? Is there an implied >> reduction in MTBF each time I cycle power on a drive (i.e. minus NN% >> MTBF per power cycle)? > >Hard drives, like most computer equipment, undergo more stress when powering >on and warming up than if left running. True, but where is the cut-over? It appears that in normal use, i.e. not being turned on and off a dozen times or more per day, operating time is the more important factor. Otherwise, the equipment would probably be rated in MPCBF (Mean power-on cycles before failure). Why would cost-conscious manufacturers bother to build in a power switch if they expected the customer to leave the equipment powered on all the time? Also, I have yet to read a computer manual that recommends to leave the power on, though most of them talk about shutdown procedures. Not even for the MacPlus, which has been prone to power-supply-circuitry failure, did Apple Computer recommend leaving it on. Wolfgang N. Naegeli University of Tennessee & Oak Ridge National Laboratory Internet: wnn@ornl.gov Bitnet: wnn@ornlstc Phone: 615-574-6143 Fax: 615-574-6141 (MacFax) QuickMail (QM-QM): Wolfgang Naegeli @ 615-574-4510