Once upon a time I was a “technical support engineer” for a computer dealer, and in those days I worked on the CDC and Diablo44B 10M drives. These machines were huge, easily weighing in at about 150lbs each. They had a fixed platter and a removable double sided diskpack of 5M capacity. The 4 heads were mounted on a voice coil and a very big heavy magnet along with a huge transformer and steel chassis made up the weight of these machines. Between the Diablo and CDC, I found that the CDC was the more reliable of the two. We very rarely did component level repairs on the drives, but head and platter changes were the norm on the Diablo’s. These drives had very high quality filtration systems and the read/write heads floated on a cushion of air when they were loaded and a head crash was when the head physically contacted the platter. Head crashes were a common occurrence for these units, because they were supposed to be housed in a climate controlled environment and would ordinarily be very reliable, however our customers very rarely seemed to adhere to this practise. A speck of dust could literally crash a drive.
When a crash occurred the drives were brought into the workshop (manually carried up 3 flights of stairs I might add) and part of my job was to get it back to working condition once again. First I would strip out the old platter, heads and filters, then service and clean what had to be done, then install a new platter, filter and heads and then start her up. A bad crash would leave the drive full of iron filings and I found Prestik very useful. We would leave the machine to purge and get to operating temp before attempting to do the alignment. The variations in temperature were catered for in the drive but our workshops were not dustfree nor air conditioned so we had to make sure that we monitored the ambient temperature. The removable platter in the Diablo was located under the circular aluminium cover in the bowl.
|Diablo 44B 10M disk drive|
The head alignment was critical, and it involved getting the heads to be not only 90 degrees to the axis of the machine, and aligned to each other. The top heads were very critical as they had to read the boot sector of the removable platter. A removable disk was theoretically readable on any correctly aligned disk drive, and a removable disk that did not read on a correctly aligned drive was either faulty or the alignment of the drive it was written on was out of spec. The drive was hard sectored and the sector marks were on the disk hubs. The sensor that read the sector marks on the hub had to be the correct distance from the sector marks and aligned at the correct angle to the marks. You can see the sensor (white object in the disk bowl) in the first image above. We used a special removable disk called a CE pack to do the alignment with as well as an oscilloscope and lots of patience. Once you put the diskpack into the bowl and closed the side latches the drive would be started, as it started the latches would be locked with solenoids and as the disks spooled up a set of motor driven brushes would sweep out of a recess next to the heads and brush across the platters as the machine got up to speed. The next event would be the heads loading, with a resounding “thunk” noise. A grinding noise was bad news.
The voice coil could be manually operated by a switch and our hearts would give a little bump when we triggered those heads to load the first time. With the voice coil switched off you could manually move the heads backwards and forwards along the spinning disk. Once alignment was done we would run diagnostics after formatting the bottom surface. There were a few things we could do, but mostly we would copy one good working disk to the bottom platter and then run a compare between it for a few hours. We were also able to read individual sectors using a utility called “hzap” and could manipulate the data within.
I also used to work on the Phoenix 96 MB HDD’s although I was only limited to filter and head changes as well as cleaning and purging. The head alignment on these drives was even more critical, and the wrong move could crash the drive, and, when they crashed they did so spectacularly. I seem to recall that they had 2 fixed disks and 1 removable disk (6 heads in total), and they had to operate within even stricter parameters of temperature and dust. One of our customers had at least 18 of these beasties and their computer room had its own underfloor air con running 24/7 to keep them within the operating temperatures.
|Phoenix 96M disk drive|
The Phoenix was very similar in operation to the 10M drives, although much more critical because it was a quicker drive and had a much greater capacity (96M as opposed to 10M). I seem to recall that the one fixed patter was written with the sector information which made the fixed surfaces soft sectored. The Phoenix also had a lo air/no air sensor in its filter and a special latch on the front door that would be locked by a solenoid. The diskpack was also slotted into a front loading tray which meant that you could stack drives on top of each other, the 10M’s you had to move the drive forward on rails to drop the diskpack in.
The drives were connected to a file controller via flat ribbon cables with Winchester connectors on and these were very prone to going faulty, more so than the drives were.
When we started getting into the mini computer business the drive footprints became smaller, and the first 5¼” drives were used in place if the larger units. The capacity of these drives was not great, but then we did not have operating systems that used gigabytes of space. My first HDD on my XT was a Seagate ST225, which was slightly faulty. It would not boot in cold weather as there was a problem with the the first few sectors of the drive. I used it as storage only, booting into DOS from a floppy disk instead.
As technology improved so the capacity of the drives increased too, and soon we no longer saw the large full height 5¼” HDDs, instead the smaller 3½” drives became the norm.
Both of the drives pictured above are years out of date. The ST412 being introduced in 1981, and the ST3850 round about 1996. The ST225 was introduced in the mid 1980s.
An interesting look at how those early hard drives developed may be found at http://www.redhill.net.au/d/i.php.
On the removable storage side of things I encountered the large 8½” floppies, 5¼” and 3½” units, and had varying success with all of them, although the 3½” did seem to be the most unreliable of the lot. The nice thing about the early personal computers was that your operating system could fit on a 360K floppy, and if you had a dual floppy machine like I did you could use them quite effectively. My beloved Wordstar 4 ran very well on my XT with its CGA monitor, 512K RAM and dual floppy drives. I was also involved with the repair of some of our units that had the 8½ floppy disks, but they were really at the end of their lifespan and all we were doing was delaying the inevitable.
Nowadays we are inundated with so many different options when it comes to storage, although the size of our data files can be staggering too. I find it ironic that many of the files I have on my current computer are larger in size than the full capacity of a Phoenix, or even an ST3850. The drive technology has changed too, and when I started out in computing it was said that hard disk technology was comparable to flying a jumbo jet a metre off the ground and counting each blade of grass. Today it is probably akin to flying Concorde 6 inches above the grass and cutting each blade, repainting it and gluing it back on, while drinking a cup of tea and watching the inflight movie.
All I know is, you will always run out of space!
© DRW 2004-2018. Recreated 05/01/2015. ALL RELATED ITEMS, CHARACTERS AND DESIGNS ARE TRADEMARKS OF THE VARIOUS COPYRIGHT HOLDERS. ALL RIGHTS RESERVED.