Note 1998-10-06: Although most of the HP tape drives that use 67 and 134 MB 1/4-inch cartridges are now off support life and out of use, I still see this question raised from time to time. Note 2002-07-19: Note that this information does NOT apply to DAT/DDS, DLT or Ultrium tape media. ________________________________________________________________ Net standard answer number 600HC... Edition: Early 1990s Audience: World-Wide re: > The bottom line is: > one cannot convince a Sun to read a HP-UX tape. True. About once a year, an unhappy customer asked: "Can I use cartridges to move data between my HP and my XYZZY systems?" ...and less frequently... "Why did my XYZZY system ruin my HP tape!?". The answers are... - no, you can't, and - yes, that can happen There are a number of formats employing seemingly identical 1980s-vintage 1/4-inch cartridges. The most common were the various QIC definitions (QIC = Quarter Inch Committee). Sun and Apollo systems, for example, often used QIC-24 (60 Mb). Traditional HP drives did not use the QIC format, but rather one invented by 3M (now Imation) a few years before QIC. It is called HCD format, but since this abbreviation never came into widespread use, it is generally differentiated by number of tracks: 16 for HCD-75, 32 for XTD-134. Inserting an HP cartridge in a QIC drive leads at the very least to frustration, and potentially to permanent damage to the HP tape. -------------------------------------- The one-minute summary Using a QIC tape in an HP 16- or 32-track drive results in: 0. Tape rejected. 1. Possible tape unspool after repeated attempts. Using a 16- or 32-track tape in a QIC drive results in: 1. No data exchanged. 2. An apparently damaged tape (rewind scenario). 3. A probably destroyed tape (reposition spill scenario). 4. A definitely destroyed tape (write scenario). -------------------------------------- Cartridge Tape Specification Overview: .================.=====================.====================. | Characteristic | HCD Cartridge Tape | QIC Cartridge Tape | |================+=====================+====================| | Approx. Incep. | 1980 | 1985 | | date | | | |----------------+---------------------+--------------------| | Mechanical | 3M DC600 | 3M DC600 | | form factor | | | | Merchandising | | QIC-24 or QIC-120 | | name | | | |----------------+---------------------+--------------------| | Typ. supplier | HP (HP customers) | any discounter | |----------------+---------------------+--------------------| | Generic | DC600HC, DC615HC, | DC600A, DC615A | | designation | DC600XTD, DC615XTD | | |----------------+---------------------+--------------------| | Tape | Full-track 3M | | | pre-format | HCD-75 or | | | | modified XTD-134 | | | Data format | MFM | RLL 1,2 within | | | modified XTD-134 | NRZI | |----------------+---------------------+--------------------| | EOT/BOT | Delimited by | Optical tape | | | pre-format | sense holes | |----------------+---------------------+--------------------| | Rewind | Right spool empty. | Left spool empty. | | position | | | |----------------+---------------------+--------------------| | Capacity | 67 or 134 Mbytes | 60 or 120 Mbytes | | Number | 16 or 32 tracks | 9 or 15 tracks | | of tracks | | | |----------------+---------------------+--------------------| | Access types | Random | Serial only | | | (re-writeable) | | | | or serial | | | Average seek | 2 minutes | 20 minutes | | (60M) | | | |----------------+---------------------+--------------------| | Error control | Read-while-write | Read-while-write | | | (on HP drives) | plus CRC | | | plus XOR ECC | | `===========================================================' As you can see, 16-track had some advantages. Errors missed by read-after-write may still be corrected by ECC (XOR blocks) when read later. Tapes may be "certified" and re-certified by end users, sparing bad blocks. The random-access capability allows software to treat the tape like a *very* slow disk drive. Disk-image cartridge tape backups are mountable as read/write volumes, and may be safely written upon. Random access is faster, because the location of every record can be calculated, due to the pre-formatting. An exhaustive search is not required. This two-decade-old format has given us satisfactory service. But, enough drifting away from the topic... 16/32-track and QIC cartridges are mechanically identical. A 16- or 32-track cartridge will fit in a QIC drive, and vice-versa. So what is the problem? * 16- and 32-track tapes are preformatted by 3M or a 3M licensee. A full-track factory write head lays down fixed physical records on the tape. No 16- or 32-track end-user drive ever writes on these record headers (called "keys"); only in between them. HP "format" and/or "mediainit" user processes merely "certify", performing read/write tests, sparing bad blocks and updating logs. The read/write heads in the drives are either 1/16- or 1/32-track. Keys, being full-track, cannot be re-written in the field. * The keys also do not extend to the physical BOT/EOT sense holes in the tape. When the first HP drives were developed in the early 80s, optical sensing was deemed too unreliable, so all HP drives use boundary keys to denote BOT/EOT. (QIC tapes are more like traditional 1/2-inch 9-track media. The tapes have no pre-formatting, so QIC drives must rely on the sense holes for BOT/EOT.) * If you put a QIC tape (blank or written) in an HP 16- or 32-track drive, the HP drive will search "uptape" (wrong way past EOT on QIC) for the nearest key, fail to find one, time-out, buzz, release (unload) the tape and illuminate the FAULT indicator. No data lost, but no data is read or written either. Caution: Repeated attempts risk a tape spill. * If the you put a 16- or 32-track tape in a QIC drive, the drive will "rewind" it (to the wrong end of the tape by HP conventions) and OUTSIDE the keys region. Suppose the tape is removed from the QIC drive and re-inserted in an HP drive. The HP drive, as in the preceding example, will search "uptape" for a key (again, in the wrong direction due to the QIC rewind), not find a key in a reasonable time, and reject the tape for fear of spilling tape if the search continues. It will buzz, release and FAULT. Caution: Repeated attempts risk a tape spill. The tape may be MANUALLY wound, in the COUNTER-INTUITIVE direction, to reposition it inside the keys. If re-inserted in the HP drive, it will properly load (after adding an extra minute to the load time because it was rewound to the wrong end). I say "counter-intuitive" because tape motion inside the cartridge is in the OPPOSITE direction from drive wheel motion, and the tensioning band makes it difficult to assess which way the tape is supposed to spool. Now, also please note that in the construction of DC600 media (all formats), the tape ends are not affixed to the reels... * Given a mis-positioned cartridge, should someone manually wind in the intuitive {i.e. incorrect} direction, or risk repeated access attempts, the tape unspools. Disassembly and re-spooling of DC600 tapes is a nightmare for the inexperienced. In a past life I re-loaded several DC100A cartridge tapes. Not fun. The probability of reloading the tape without damage is low. * If, on the other hand, the 16- or 32-track tape was left in the QIC drive, two more scenarios obtain. The QIC drive has no clue that this is an HCD tape. 1. The HCD data structures just look like noise. Any attempt to read an HCD tape simply fails or returns garbage data. If the tape is removed after a read attempt, the rewind scenario above prevails. 2. A QIC drive will happily WRITE on an HCD tape. This destroys both existing data AND the HCD preformatting keys. If the preformatting is ever lost, the tape can NEVER be used in an HCD drive again. (This problem can also happen subsequent to degaussing an HCD tape.) What happens back at the HP drive? Apart from the rewind/time-out problem, as soon as the HP drive detects a trashed key, it will FAULT and reject the tape. Only 3M could (re)format an HCD tape, and I doubt that Imation now offers such a service. These scenarios are not hypothetical. It happens. Let's be careful out there. If you have a tape labelled DC6xxHC, DC6xxXTD or with the [(hp)] logo on it, don't insert it in a tape drive not known to be HP-compatible. Final Note: NEVER degauss an HCD tape (unless you deliberately want to turn it into a QIC tape). Regards, PO Box 248 Bob Niland Enterprise mailto:name@isp-name.domain Kansas which, due to spam, is: 67441-0248 USA rjn AT access DASH one DOT com