Unix-Projects-3b2/3b2-Tape-Drives.txt

Edited 1-13-2024

There have been two major families of cartridge tapes on the 3B2 family,
and they are not at all interchangeable. We'll describe them here in
case you're sorting through what's in front of you.

23MB Cartridge Tape Drive Model 3b2-400

The first tape drive available for the 3B2 family was the 23 megabyte 
Cartridge Tape Drive, and these are not compatible with any of the 
later SCSI drives. It was standard equipment on the 3B2/400 and was 
available in the XM expansion module for the 3B2/300, /310 and the /400. 
As far as we know, the 3B2 is the only system that can read these tapes.

These units use the CTC driver and are accessed via the device 
/dev/rSA/ctape1. There is a special ctccpio command that is able to put 
the device into streaming mode, but we've seen enough problems with 
this command that we prefer to use the standard cpio command for this 
even though it's a bit slower. A noticeable feature of the non-streaming 
mode is the very annoying back-and-forth running of the tape while 
reading: we've heard it described as "wheezing".

A particular oddity of these tape drives is that because they "look" 
like a (very large) floppy disk drive, the drive provides a block device 
interface (/dev/SA/ctape1), in addition to the expected character 
(aka "raw") device interface (/dev/rSA/ctape1. This means that it's 
possible to mount a tape drive as a filesystem. It works, but it's so 
slow that it's hard to convey just how painful this is.

Our particular unit is a Cipher FloppyTape 525 (model 960273), and it is 
branded with AT&T part number KS-23165. It uses a floppy disk interface 
with the familiar 34 pin card-edge connector as found on older 5-1/4" 
floppy drives. A distinguishing mark of this drive is the flip-up lever 
that is used to engage the tape after insertion: most of the drives 
shipped with the 3B2 were of this type. We understand that there is also 
a similar drive made by Wangtek that looks very much like the SCSI units.

Our understanding of these drives is that they should not use the same 
DC600 cartridge tapes as do the 60 and 120 MB SCSI drives, but after 
recently reviewing the 3B2 service documentation we are no longer of 
this view: AT&T says that DC600 tapes can be use in all their drives. 
This is good news: we've been telling people for 10 years that they have 
to use special tapes. Oh well.

It is possible to add a 23 MB tape drive to the 3B2/600 and newer units: 
we simply install the CTC I/O card (CM195H) into the 3B2/600 and install 
the CTC driver. We've done this on our system, though the mechanical 
arrangements are "suboptimal". Because the 23MB drive doesn't really have 
any provisions for external cabling. the only real way to do this is to 
mount the 23MB unit inside the cabinet and put the displaced SCSI tape 
drive into an external case: then use "regular" external SCSI cables to 
connect them.

This "floppy tape" interface is used in other computer systems, including 
many on the PC. As such, the Linux floppy tape project might prove fruitful 
for those determined to read and write many tapes on their own systems. 
We are not even close to motivated enough to try this ourselves, but we'd 
surely love to report on the experiences of others.

60/120MB SCSI Tape Drives Model 3b2-700

The 3B2/600 and later models (including the low-profile /522) all came with 
SCSI tape drives of either 60 or 120 megabyte capacity, and these are 
standard units as found in many other pieces of equipment.

We believe that AT&T only used Wangtek drives, and they are of the type 
where you push the tape in, hear a click, and let go: now the drive is 
engaged. To release, just push again and the tape pops out. The drives 
from AT&T have a small "60" or "120" stamped on the faceplate to report 
the capacity.

These drives all use the ST01 driver, and the device name is /dev/rSA/qtape1. 
Not surprisingly, there is no block device.

A 120 MB drive can read a 60 megabyte tape but cannot write one. Neither 
of these drives can read or wrote the 23 MB format. Sorry.



From Steve Friedl's 3B2 Tech Tips unixwiz.net/3b2/tapedrives.html