emmo@moncam.co.uk (Dave Emmerson) (11/20/89)
I tend to read this group rather than post to it, but I can't resist this one, it tickles me pink.. There's been a lot of slagging-off of RLL drives, and praising of SCSI (and acceptance of MFM as cheap but reliable). I've just re-read the much vaunted Quantum PRO80S's manual to confirm my suspicions, and it's TRUE, section 2, page 1 of the Installation Manual for this Embedded SCSI drive has an entry Encoding scheme RLL 2,7 Pick the bones out of that one then! Dave E.
norsk@sequent.UUCP (Doug Thompson) (11/23/89)
In article <286@marvin.moncam.co.uk> emmo@moncam.co.uk (Dave Emmerson) writes: > >There's been a lot of slagging-off of RLL drives, and praising of SCSI >(and acceptance of MFM as cheap but reliable). I've just re-read the >much vaunted Quantum PRO80S's manual to confirm my suspicions, and it's >TRUE, section 2, page 1 of the Installation Manual for this Embedded >SCSI drive has an entry >Encoding scheme RLL 2,7 > >Pick the bones out of that one then! > At the end of each target is a controller that handles the SCSI-Drive interface. That drive interface could be anything: AT, 506, MFM, RLL, SMD IPI, etc. SCSI itself is not a drive interface but a device interface. And the device interface can be constructed to handle not one but upto 8 devices per target. Its possible to have a fast SCSI bus adapter and SCSI bus, and several types of target controllers - fast, slow, medium. Flexibility - its great. -- Douglas Thompson UUCP: ..{tektronix,ogcvax,uunet}!sequent!norsk Sequent Computer Systems Phone: (503) 526-5727 15450 SW Koll Parkway !"The scientist builds to learn;the engineer learns in Beaverton OR 97006 !order to build." Fred Brooks
mrichey@orion.oac.uci.edu (Mike Richey) (11/23/89)
In article <286@marvin.moncam.co.uk> emmo@moncam.co.uk (Dave Emmerson) writes: > >I tend to read this group rather than post to it, but I can't resist >this one, it tickles me pink.. > >There's been a lot of slagging-off of RLL drives, and praising of SCSI >(and acceptance of MFM as cheap but reliable). I've just re-read the >much vaunted Quantum PRO80S's manual to confirm my suspicions, and it's >TRUE, section 2, page 1 of the Installation Manual for this Embedded >SCSI drive has an entry >Encoding scheme RLL 2,7 > >Pick the bones out of that one then! RLL 2,7 and 1,3 MFM are encoding methods. How magnetic flux is placed onto the surface of a platter. On an RLL 2,7 encoding scheme, you will about fifty percent more data onto the disk, however the amount of magnetic flux is the SAME between MFM and RLL. Now, ESDI, and SCSI are electrical and command specifications for a particular interface type. ST506/412 is another interface specification. As an example the Seagate ST225 is an MFM encoded, ST506 drive. The CDC (Imprimis) 94166-155 is an ESDI interface, RLL encoded 150Mbyte drive. The ST238, is an ST506, RLL encoded drive, and so on. Encoding and interface are two different things. Please consider the following an opinion...... The What has made RLL seem like a bad scheme to some people is because of failures of some of the less expensive drives sucha as the Seagate ST238s. Now I know lots of people that have ST238s and swear by them. But I also know lots of people that swear at them. There are dealers about that refuse to sell the Seagates. I spoke with an engineer (not a phone support person) at a company called Silicon Systems. They produce the part that Seagate uses on the HDA to detect the magnetic flux as it passes under the heads. It form an electrical signal from these magnetic flux patterns. Okay, the one Seagate uses apparently is an old design. SSI has recommennded that Seagate switch to a newer (read more expensive) design, because of potential problems with the older part. Well they're still using it. SSI makes them, but has not improved the part for years, and won't. Let's just say I ran across this information while working on a proto type of a non standard hard disk controller. Seagate ST238s and the ST225s for that matter, they use the same pulse detector, won't work on this controller. A Kalok, Fujitsu, and other newer designed drives will. Any drive that uses this pld SSI design didn't work. The other drive that didn't work was the miniscribe 8438 and 8425 (3 1/2 inch RLL and MFM encoded drives). Guess what? SSI told us that the same poulse detector is used in that set of drives. Well take it for what it's worth. End of opinion.... Michael S. Richey University of California, Irvine - Network & Telecommunications Services InterNet: mrichey@orion.oac.uci.edu BitNet: MRichey@UCI CompuServe: 71650,3132 Voice: (714) 856-8374
liberato@drivax.UUCP (Jimmy Liberato) (11/23/89)
emmo@moncam.co.uk (Dave Emmerson) writes: >There's been a lot of slagging-off of RLL drives, and praising of SCSI >(and acceptance of MFM as cheap but reliable). I've just re-read the >much vaunted Quantum PRO80S's manual to confirm my suspicions, and it's >TRUE, section 2, page 1 of the Installation Manual for this Embedded >SCSI drive has an entry >Encoding scheme RLL 2,7 >Pick the bones out of that one then! It wouldn't be fun if it wasn't confusing! I don't think the SCSI controller chip knows or even cares what kind of physical format the DMA controller/data sequencer chip is encoding the bit stream as. One's logical, the other is physical. Yeah, I know, an oversimplification but isn't that the magic of SCSI, its transparency? Rather, the transparency to the SCSI bus of the more physical things like media defects, interleave, and format? I defer to the SCSI gurus out there (or to anyone who has actually slogged through ANSI X3T9.2/82-2). I do know that most of the high-end embedded SCSI drives are RLL 2,7. What do the others use, something proprietary? -- Jimmy Liberato ...!amdahl!drivax!liberato
hase@netmbx.UUCP (Hartmut Semken) (11/26/89)
In article <256BAE8C.79F@drivax.UUCP> liberato@drivax.UUCP (Jimmy Liberato) writes: >I defer to the SCSI gurus out there (or to anyone who has actually slogged >through ANSI X3T9.2/82-2). I do know that most of the high-end embedded >SCSI drives are RLL 2,7. What do the others use, something proprietary? True, as far as I know. Some drives use RLL3,9 (to get some more capacity) and slower rotation speeds. For example, the Seagate 296N (80 MB, half height) and 251-1 (MFM 40 MB) have the same number of heads and cylinders. hase -- Hartmut Semken, Lupsteiner Weg 67, 1000 Berlin 37 hase@netmbx.UUCP Dennis had stepped up into the top seat whet its founder had died of a lethal overdose of brick wall, taken while under the influence of a Ferrari and a bottle of tequila. (Douglas Adams; the long dark teatime...)