Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!gatech!hao!scdpyr!faulkner From: faulkner@scdpyr.UUCP (Bill Faulkner) Newsgroups: comp.sys.mac Subject: Re: Using single-sided disks double-sided. Message-ID: <110@scdpyr.UUCP> Date: Fri, 12-Jun-87 12:58:38 EDT Article-I.D.: scdpyr.110 Posted: Fri Jun 12 12:58:38 1987 Date-Received: Sat, 20-Jun-87 18:45:39 EDT References: <5352@ut-ngp.UUCP> <1029@zog.cs.cmu.edu> <9766@duke.cs.duke.edu> <3303@sdcsvax.UCSD.EDU> Organization: Natl Ctr Atmospheric Research, Boulder, CO Lines: 51 Summary: Hopefully the final word There has been much disccussion lately about using SS disks as DS disks. It reminds me a lot about people trying to be cheap with memory and using 200ns memory instead of 150ns memory chips. Basiclly when you purchase a SS disk (or 200ns memory) the manufacture will guarentee it for its rated capacity only. About 90% of the time, one can use it as a DS with absolutely no problem. The other 10% is what you should be worried about. A DS disk (or 150 ns memory) will work at the higher rate (except in rare cases when the manufacture will replace it free). The only real difference between SS and DS disks (or 200ns and 150ns memory) is that the manufacturer has verified both sides of the DS disk as being good. The SS disk is usually identical to the DS, except that one side did not pass the DS test. This is similar to the memory situation where a single batch of chips, using the same mask, can contain 200ns chips, 150 ns chips, and 120ns chips. The chips are tested and the ones that pass certain speed tests are rated higher. In other words, The SS disks are actually rejects of double sided disks (well maybe not all of them, but if a proposed DS disk fails verification on the right side and the other side passes the manufacture will sell it as SS.) Now I have used SS as DS disks with little problem. However, it is used for transporting data that I can easily restore. I do not trust SS disk used as DS disks for anything I can't get an easy copy of. Therfore, those of you who want to save $.25 a disk, go ahead and buy SS disks, but don't come crying to the manufacturer when you lose data. I do suggest that you buy and use DS disks for any data you don't wish to lose (it's not guarenteed 100% save, but is a lot safer than SS disks). I will guarentee you that I will only use high quality DS disks for the back up of my hard disk. It isn't worth the risk to use my old SS disks as backups. A quick note about the verify option on several disk utilities. These routines are now where as thourgh as the disk manufacturers use. They are similiar but are single pass (i.e. reads and/or writes each track once) where as the manufacturer will read and write maybe 100 times. The verify option of these disk utilties are designed to allow you to verify that you have a problem with a specific disk (i.e. the mac won't copy some documents onto a disk that has plenty of space). You can then run the verify and see if the disk has an error, if so you can try to reformat the disk, thus eliminating the error. They are not designed for verifying that the disk media itself is alright. In summary, go ahead and use SS as DS, but if you care about the data you are storing, use DS. faulkner -- Bill Faulkner * NCAR (Nat'l Center for Atmospheric Research) PO Box 3000 * Boulder, CO 80307-3000 * 303-497-1259 UUCP: faulkner@scdpyr.UUCP or ..!hao!scdpyr!faulkner INTERNET: faulkner@scdpyr.ucar.edu ARPA: faulkner%ncar@csnet-relay.arpa