Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!newstop!texsun!alanya!lupe From: lupe@alanya.Germany.Sun.COM (Lupe Christoph - Sun Germany Consulting - Munich) Newsgroups: comp.sys.amiga Subject: Re: SCSI vs. ST506 vs. ESDI vs. Whatever else there is??? Message-ID: Date: 25 Sep 90 20:57:58 GMT References: <184@thor.UUCP> <1990Sep21.225835.20649@psuecl.bitnet> Sender: news@texsun.Central.Sun.COM Lines: 48 I'd like to add a few things to this very good summary. First of all, with disk interfaces, you may have different widths of the data path. ST506 takes the bitstream from the disk, as far as I'm aware, with the clock bits, and lets the controller in the host decode. This is why you can buy MFM and RLL controllers for ST506 disks. ESDI (I believe) does data separation on the disk side, so you have no choice of encoding.. I also *believe* you still have a bitstream. Maybe not. SCSI has an 8 bit wide data path, with 16 bits coming as an option in SCSI-2. The "ATbus" (that for disks, not that for controllers) has 16 bits, I believe. SCSI and AT use a high-level interface that works with command packets. ST506 and ESDI toggle lines. E.g. to read a sector from some track on some cylinder, you twiddle lines to step the head, then set some others to select the head, the take the bitstream until you got the sector. In SCSI, you tell the disk to get you logical sector #so-and-so. This number counts the sectors on the disk from cyl 0, trk 0, sec 0 up. There are also some interface standards that are not (currently ?) used in the micro world. That's SMD, ESMD, and IPI. SMD is much like ST506 for discussions like these, just faster. ESMD is the same feature-wise, just even faster. BTW, SMD stands for Storage Module Drive, a line of disks manufactured by CDC (today, Imprimis) way back in the 70s. ESMD is Extended/Enhanced or some other noise word SMD. Oh yeah, ST506 is Shugart Technology drive type 506. SCSI means Small Computer Systems Interface. AT is Advanced Technology. I don't know what IPI stands for, maybe Intellegent Peripheral Interconnect. It is somewhat like SCSI, but faster. Haven't seen much of it myself yet. Sun is using it in the high-end machines. Disks have around 1GB, typically. Transfer rate is 3 MB/sec or even 6 MB/sec. -- | lchristoph@Sun.COM (Internet) | Disclaimer: | | ...!unido!sunmuc!lupe (German EUNet, "bang") | My employer has a | | lupe@sunmuc.UUCP (German EUNet, domain) | non-exclusive license | | ...!suninfo!lchristoph (Sun Germany customers) | to my opinion. |