Path: utzoo!attcan!telly!eci386!clewis From: clewis@eci386.uucp (Chris Lewis) Newsgroups: comp.lang.postscript Subject: Re: Bitmap of PostScript code.. Message-ID: <1990Feb23.182430.17416@eci386.uucp> Date: 23 Feb 90 18:24:30 GMT References: <8167@lindy.Stanford.EDU> Reply-To: clewis@eci386.UUCP (Chris Lewis) Organization: Elegant Communications Inc., Toronto, Canada Lines: 51 In article <8167@lindy.Stanford.EDU> ralerche@lindy.Stanford.EDU (Robert A. Lerche) writes: > A simple way to grok disk speed: 60 revolutions / second is the typical > hard disk speed. So, with 17 sectors on a track (again, typical), 512 > bytes/sector, we have around 500 K bytes/second (about 30 M bytes/minute) > at 1:1 interleave. Eg: this is *absolute* maximum thruput from a ST506 drive - no missed rotations, exactly one rotation per track, 1:1 interleave. This is rather hard to achieve (or utilize for that matter) in most cases.... Some benchmarks I've done suggest that typical random reads of 4-8K through UNIX buffered disk devices (not files) is typically *less* than 1/4 of that. A surprising number of "reasonable" machines get an effective bandwidth of 25-50K/sec at most.... Micropolis 1570 (SCSI) or 1550 (ESDI) series, on the other hand, is 512 (sectorsize) * 36 (sectors/track) * 3600 / 60: 1105920 bytes/sec. (Most other SCSI and ESDI drives should be the same, if not a bit more depending on bit encoding) So, roughly double the effective bandwidth - though, some disk drivers are capable of doing considerably better. > ... So, using raw bitmaps it's a problem to drive a 100 > page/minute marking engine. You're not kidding. > However, with some fairly simple compression it's probably good enough. It depends on "how busy" the bitmap is. If it's text and line drawing a simple RLL encoding would work well, but rasterized images may often be a different story... > A historical note: 60 revs/second is the same speed that mainframe hard > disks have run at for years and years. Some of IBM's disks run a bit faster > nowadays (I think the current 3380's go at about 80 revs/second). The > mainframe disks have much more data per track, though, and so achieve > much higher transfer rates (up around 4 M bytes/second). CDC Hydra goes at 120 revs/sec. (US Export Control requires special licensing for drives that rotate faster than X RPM, I'm not sure whether "X" is 3600 or slightly higher) -- Chris Lewis, Elegant Communications Inc, {uunet!attcan,utzoo}!lsuc!eci386!clewis Ferret mailing list: eci386!ferret-list, psroff mailing list: eci386!psroff-list