Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!usc!zaphod.mps.ohio-state.edu!rpi!batcomputer!cornell!uw-beaver!zephyr.ens.tek.com!gvgpsa!gold!grege From: grege@gold.GVG.TEK.COM (Greg Ebert) Newsgroups: comp.sys.ibm.pc.hardware Subject: Re: info on hard disk & controller Message-ID: <1171@gold.GVG.TEK.COM> Date: 16 Jul 90 16:04:23 GMT References: Distribution: comp Organization: Grass Valley Group, Grass Valley, CA Lines: 25 In article hans@ele.tue.nl (& Fleurkens) writes: > >I'm interested in information about hard disks, hard disks controllers >such as: > >- MFM >- RLL >- SCSI MFM (Modified Frequency Modulation) This is the standard encoding technique for hard disks, and double-density floppy diskettes. The majority of the hard disk controllers are MFM. Data transfers to/from the controller are I/O read/write cycles. RLL (2,7 Run-length limited) - A data compression technique which uses narrower data windows to increase the recorded bit density by 50%. As far as the PC is concerned, it doesn't care if you use RLL or MFM, except that you will have more storage with RLL. SCSI (Small Computer System Interface) Originally developed by Shugart for hard disk interfacing, but now applicable to tape, etc. The only SCSI board I have used is made by Adaptec. It plugs into the AT and becomes a 16-bit master. Data transfer is faster than the I/O mapped MFM and RLL controllers, but this is only an important issue for UNIX or server applications. Not surprisingly, higher performance cost more.