Newsgroups: comp.sys.ibm.pc.hardware.cd-rom,alt.cd-rom Path: cdrom.com!agate!howland.reston.ans.net!swrinde!elroy.jpl.nasa.gov!decwrl!netcomsv!netcom.com!dce From: dce@netcom.com (David Elliott) Subject: Re: Too much data makes CD harder to read? Message-ID: Organization: Netcom Online Communications Services (408-241-9760 login: guest) References: Date: Thu, 11 Aug 1994 01:07:46 GMT Lines: 21 Xref: cdrom.com comp.sys.ibm.pc.hardware.cd-rom:4243 alt.cd-rom:7888 In article hoxley@max.tiac.net writes: > There are two formats for CD-R blanks, 62 and 74 minute. >The 74s have more closely spaced "grooves" than the 62s. >Thus a marginal CD-ROM drive could have problems with a 74. According to Ken Pohlmann in "The Compact Disc Handbook", the difference is the motor speed, not "groove spacing". In his words: Although the CLV [Constant Linear Velocity] of any particular compact disc is fixed, the CLVs used on different discs can range from 1.2 to 1.4 meters/second. In general, discs with playing times of less than 60 minutes are recorded at 1.4 meters/second, while discs with longer playing times use a slower velocity, to a minimum of 1.2 meters/second. Thus, the marginality of the CD-ROM drive has nothing to do with the inability to focus on the groove, but with the inability to get the motor speed down low enough. In other words, the 31A has a cheap motor. -- David Elliott - dce@netcom.com