gwyn@smoke.BRL.MIL (Doug Gwyn) (03/15/90)
Original-posting-by: gwyn@smoke.BRL.MIL (Doug Gwyn) Original-subject: SCSI hard disk for Apple II Reposted-by: emv@math.lsa.umich.edu (Edward Vielmetti) Since I just acquired one of A2Central (Open-Apple)'s 80MB SCSI hard disk kits and also have an Apple brand HD20SC to compare it with, I thought others might appreciate the following information so they know precisely what they get when they buy the kit. The A2Central kit consists of: Seagate ST296N 80MB hard disk with embedded SCSI controller, disk activity light, terminator resistor packs, one jumper (Parity enable) installed on drive configuration connector and black plastic front panel Leadman case with power supply sufficient for three drives, space for mounting two drives, power cord, fan, power-on light, more-than-sufficient mounting hardware, and a blank panel cable for connecting 50-pin PC connector on Seagate to Apple SCSI card's 25-pin (DB25) port a rather minimal instruction sheet, plus slightly misleading manufacturers' instructions for disk and case Chinook SCSI utilities, used to format and partition the disk Assembly requires one or two small Philips screwdrivers, plus a 1/8" flat-blade screwdriver for attaching the DB25 connector securely. For comparison purposes, here's what's in Apple's HD20SC: Seagate ST255N 20MB hard disk with embedded SCSI controller Apple case with power supply, space for one drive, power cord, fan, disk activity light, and mounting hardware two 50-pin SCSI (Amphenol) connectors on back panel of case cable for connecting 50-pin PC connector on Seagate to 50-pin SCSI connectors on case, including jumper between SCSI connectors, also ferrite noise suppressors externally-accessible drive priority switch and cable to connect it to Seagate configuration connector Better-than-usual Apple owner's manual with separate Mac and Apple II instructions Macintosh installation and utility software Apple brand SCSI peripherals require additional cables and external terminators, as follows: 25-pin computer SCSI port connector to 50-pin standard SCSI connector 50-pin to 50-pin SCSI feedthrough terminator at 50-pin end of above cable If and only if more than one peripheral is in the SCSI daisy chain: 50-pin to 50-pin connecting cable between peripherals additional SCSI feedthrough terminator on last peripheral In all cases you also need an Apple SCSI card installed in your Apple II (rev C or later); it comes with the 25-pin port connector for the computer back panel, an installation manual, and minimal diagnostic software. (You're expected to use the Apple operating system or standard utilities for formatting and partitioning, but they don't work right with large disks.) What restrictions does the A2Central disk kit have? - no configuration (SCSI priority) jumpers were supplied; the default in this case was priority 0 which happens to work for a single SCSI peripheral (the computer SCSI card usually has priority 7) - changing the termination or SCSI priority require opening the case - no strain relief on the (long) cable, which merely dangles through a SCSI connector-sized hole in the case back panel - presumably there can be some RFI problems caused by this (unshielded) cable arrangement - it is impossible to daisy-chain SCSI peripherals using the supplied cable and connectors; this is fixable if you can find the parts and have the ability to make your own genuine SCSI connectors like Apple's HD20SC has (you should then use Apple's SCSI cable system for interconnects); see below - the case is long and skinny, which doesn't mesh well with the IIGS stacking-component styling (although the color is ok) What problems are there in general using large disks on the Apple II? - ProDOS filesystems cannot exceed (32K-0.5)KB, so you have to partition the disk into multiple independent filesystems - ProDOS-8 is unable to cope with more than 2 partitions on the entire SCSI system (or 4, if you're willing to give up slot 5, which on a IIGS is not usually a viable option); recent releases of GS/OS handle a sufficient quantity What advantages are there in using large disks? - more storage (obviously!) - A2Central kit accommodates a second drive, for 160MB total - Backup becomes even more crucial (if that's possible); with two inexpensive 80MB drives one could perhaps afford to use one strictly as a backup for the other Can you install the Seagate 80MB drive in an Apple HD20SC case? Almost! I started to do that, in fact, when I discovered that the 80MB drive's activity light would not be visible from the outside; it appears to be soldered to the PC board in place of the connector that Apple used to connect their separate externally-visible disk activity light. If you're willing to forgo the visible light, or to screw around with the Seagate PC board, you could fix this. The other problem is that the HD20SC uses a three-pair connector for the drive configuration, which doesn't plug very well into the 5-pair jumper block on the 80MB drive. This too isn't very hard to fix. By the way, the Seagate documentation for their 3.5" drive configuration should be used in place of the one they give for their 5.25" drives (which describes a 4-pair jumper block). Recommendations: The A2Central SCSI disk kit is well worth having and is reasonably priced. The Chinook SCSI utility software is very good (and essential, since GS/OS's Advanced Disk Utility seems unable to do the right thing when initializing such a large disk, in fact GS/OS kept crashing when I tried to use its own facilities to initialize the disk). The instruction sheet is minimal and fails to explain about priority configuration, etc., apparently on the assumption that either you're only going to have the one drive (in which case the default configuration works) or else you're going to have to find or become a SCSI connection expert anyway (see the following). Caveat: If you want to use more than one SCSI peripheral (e.g. Apple CD-ROM, or even two 80MB drives in the Leadman case), the supplied cable will be inadequate and you'll need to come up with a replacement. I suggest one like this: [ ] (Seagate 50-pin connector for top drive) | | [even if you have only one drive] | [ ] (Seagate 50-pin connector for bottom drive) | | \______ribbon_cable____{ } SCSI connector 1 | | | { } SCSI connector 2 with termination resistor packs removed from the drive(s) and Apple's SCSI cable system used (including external terminators). IIGS owners can fully utilize two 80MB drives, except that ProDOS-8 applications (yes, there still are some that are useful on a IIGS) will be unable to access other than the first two partitions on the first drive (so install system files accordingly). At least one of the two drives will have to have the termination resistor packs removed, and at least one of the two drives will have to have priority jumpers installed. (I suggest the top drive have higher priority than the bottom one, e.g. 6 and 5 respectively, as the best intuitive match to the way GS/OS will assign drive numbers to the SCSI peripherals.) You should probably invest in a good backup/restore utility (unless you're willing to use one drive to back up another). Since I don't have one I can't make recommendations here.