Storage Expansion Box in a BA42 Chassis
Although the House of VAX is primarily dedicated to the various implementations of the VAX CPU architecture, operating a VAX system requires somewhere to store the operating system. And that place is, of course, some sort of rotating media known as a Disc drive.
Invented by IBM in the 50's the hard disc was pretty revolutionary in itself. DEC spent a lot of time trying to build disc systems. My first experience was with RK05 drives on a PDP-11, then RL01 and RL02 drives. Those gave way to RM03 drives with a whopping 67 megabytes!
By the time the MicroVAX came along DEC's big drive was the RA81, it was a monster of a drive and I can't say that I have one in the collection. (My back isn't that strong!)
But let's take a moment and notice something, RK05, RL02, RM03, RA81 they all start with "R" which makes sense as they are all "Rotating" disks. But what is the second letter? As it turns out the second letter generally denotes the type of interface that connects the disk to the VAX! Here are the examples I know of:
| RDxx | MFM (Modified Frequency Modulation) Drives, connect through and RQDXn type controller. These drives are identical to the early drives used in the IBM PC and other microcomputers. |
| RAxx | SDI (Standard Disk Interconnect) which support dual porting (one port to one host and the other port to another host) |
| RFxx | DSSI (Digital Standard System Interconnect?) This is a protocol similar to SCSI and the connectors are high density 50 pin honda connectors (they look like SCSI-2 but they aren't!). DSSI drives are called ISE's or Integrated Storage Elements and have their own computer with operating system running on board the disc! Its great fun to "log in" to the disk drive and see the statistics it keeps. |
| RZxx | SCSI (Small Computer System Interconnect?) These are standard SCSI disc drives that you might use on a PC or else where, the DEC ones sometimes have unique firmware to support DEC features. |
| RMxx | Mass Bus connected disks. |
| RLxx | These connect with an RL controller |
| RXxx | Floppy drives, such as the RX50 5.25" dual drive unit common on MicroVAX II's. |
There are a zillion storage options for VAXen, however the ones I find interesting are the chassis that are re-used as storage expansion, and the very clever Storage Works line of chassis.
The collection has two examples of chassis designs that were re-used for storage expansion, one is the BA42 Storage Expansion and the other is the R215 Storage Expansion
.
Storage Expansion Box in a BA42 Chassis
The Storage expansion looks like the unit above. It has internal "sleds" to hold two drive units. The panel on the right can be replaced by other peripherals.
Storage Expansion Box with TZ-30 Tape Drive
The Expansion box above has the TZ30 tape drive installed. This tape drive is compatible with the TK50 but is a 1/2 height form factor and uses a sliding lock lever rather than the "handle" that the TK50 uses. Internally on this drive is the TK50 to SCSI bridge board.
Storage Expansion Box with RX33 Floppy
The box above is the Expansion box with the RX33 floppy disk installed. This floppy came with a floppy to SCSI bridge board making the floppy appear as a removable media SCSI device.
The Storage Works boxes are completely different, instead of re-using a VAX chassis for disks, DEC created a specific chassis that would easily hold a variety of SCSI peripherals. This concept has been used by many people today and you will see it in RAID systems, server farms, and others.
I have two examples of Storage Works products in my permanent collection, one is the the BA353x Storage Works Shelf, and the other is the BA363 Personal Shelf.