dbraun@cadev4.intel.com (Doug Braun ~) (01/06/88)
I'm confused. What is the difference between a quad density and a HD drive? How many tracks, etc., do they have? Which machines use them? (I assume the AT uses a quad density), Stupidly, Doug Braun Intel Corp CAD 408 496-5939 / decwrl \ | hplabs | -| oliveb |- !intelca!mipos3!cadev4!dbraun | amd | \ qantel /
wtm@neoucom.UUCP (Bill Mayhew) (01/08/88)
Typical 5-1/4 inch disk designations: DD (Double Density): 360K formatted capacity (when both sides are used). 40 tracks, 9 sectors/track. IBM also supports 160K/320K 8 sector/track formats. 4D (Quad Density): 720K formatted capacity. 80 tracks, 9 sectors per track. HD (High Density): (used on PC/AT) 1.2 meg fromatted capacity. 80 tracks, 15 sectors/track. A High Density drive can be made to read any of the above formats, and usually write them. High Density disks formatted to 360K or 720K can be *read* but *not written* to reliably by the other drive types. HD diskettes are sort of like trying to use metal cassete tapes in a regular cassette player. The DEC Rainbow also has a bastard 400K single-sided disk format that uses 4D media. --Bill
Usenet_area_"Cs.I.Pc"@watmath.waterloo.edu (01/09/88)
From Usenet: cbosgd!mandrill!neoucom!wtm From: wtm@neoucom.UUCP (Bill Mayhew) Newsgroups: comp.sys.ibm.pc Subject: Re: What are these? Summary: disk formats Message-ID: <922@neoucom.UUCP> Date: 8 Jan 88 15:01:50 GMT References: <1535@mipos3.intel.com> Organization: Northeastern Ohio Universities College of Medicine Lines: 25 Typical 5-1/4 inch disk designations: DD (Double Density): 360K formatted capacity (when both sides are used). 40 tracks, 9 sectors/track. IBM also supports 160K/320K 8 sector/track formats. 4D (Quad Density): 720K formatted capacity. 80 tracks, 9 sectors per track. HD (High Density): (used on PC/AT) 1.2 meg fromatted capacity. 80 tracks, 15 sectors/track. A High Density drive can be made to read any of the above formats, and usually write them. High Density disks formatted to 360K or 720K can be *read* but *not written* to reliably by the other drive types. HD diskettes are sort of like trying to use metal cassete tapes in a regular cassette player. The DEC Rainbow also has a bastard 400K single-sided disk format that uses 4D media. --Bill --- via UGate v1.6 * Origin: watmath (221/163)
Ralf.Brown@B.GP.CS.CMU.EDU (01/14/88)
In article <675@bucket.UUCP>, leonard@bucket.UUCP (Leonard Erickson) writes: }Single density disks (which do exist in 5.25!) use FM recording. This is }data-bit clock-bit data-bit..... } }Double density disks (and QD & HD & "normal" hard disks) use MFM. This }uses some sort of scheme (I forget the details) to make the data }"self-clocking" and thus eliminate the clock-bits. This enabled twice }the data density, thus the term double-density. MFM is really RLL 1,3 (i.e. at most 3 zero or one bits in a row). The RLL controllers use RLL 2,7 (at most 7 identical bits in a row), and ARLL uses (I think) RLL 3,9. }For what it is worth, if the PC had supported single density disks }(which would take a different controller chip!) it would have had Actually, the controller is perfectly capable of handling single density. One of the bits in the command code that is sent to the controller indicates whether to use FM or MFM. }Leonard Erickson ...!tektronix!reed!percival!bucket!leonard }CIS: [70465,203] -- {harvard,uunet,ucbvax}!b.gp.cs.cmu.edu!ralf -=-=- AT&T: (412)268-3053 (school) ARPA: RALF@B.GP.CS.CMU.EDU |"Tolerance means excusing the mistakes others make. FIDO: Ralf Brown at 129/31 | Tact means not noticing them." --Arthur Schnitzler BITnet: RALF%B.GP.CS.CMU.EDU@CMUCCVMA -=-=- DISCLAIMER? I claimed something?