The Hard Facts on Hard Discs

David Spencer looks at the hard disc upgrades from Watford Electronics and Acorn, and gives some practical advice on managing a hard drive.

I'm sure that if you asked all Archimedes owners what upgrade they most wanted, then a hard disc drive would just beat a multi-sync monitor into first place. This is hardly surprising when you compare the speed and elegance of a hard disc to floppies. Not only does it offer loading and saving many times faster than a floppy, but also a 20Mbyte hard disc can hold the equivalent of almost 25 floppies. However, as always, luxury costs, and to many owners a hard disc upgrade represents a considerable investment. In this article I shall take a closer look at hard disc systems, and compare the two most popular upgrades currently available.

WHAT'S IN A DRIVE?

Before looking at individual products, let us look briefly at what makes up a hard disc system, and how it differs from a floppy. As with a floppy system, there are two main parts - the disc controller and the drive itself. In both cases, the controller consists of a collection of chips, and other components, which for a floppy are mounted on the Archimedes' main circuit board. On a 400 series computer the hard disc controller is also mounted on the main board, and in fact there is provision for this on the 300 series. However, all the relevant pads on the circuit board are clogged with solder, and a much simpler solution is to put the hard disc controller on a podule which mounts on a backplane. Wherever the controller is located, the software to access it is provided as standard in the ADFS module, and this therefore forces any hard disc upgrade to use the same controller chip (an Hitachi HD63463 to be exact). This also means that from a software point of view all hard disc upgrades are identical.

Turning to the drive, in many ways a hard drive is similar to a floppy. But, unlike a floppy, a hard drive consists of more than one disc (normally two), and these are all mounted on the same spindle and driven by the same motor. Each side of every disc has its own read/write head, and these are all moved by the same stepper motor. A hard disc is split into many more tracks than a floppy - typically 620. The main difference between a hard drive and a floppy is the positioning of the heads. On a floppy the heads sit tight against the discs. This causes wear, and at the increased speed of rotation of a hard disc would be impractical. Therefore, in a hard drive the heads float very slightly above the surface of the disc on a layer of air that is forced through the drive spindle by a fan mounted on the spindle, and then out through holes over the discs. This means that there is effectively no wear on the disc or the head. The entire drive mechanism is enclosed in an air-tight package, the air within being free of dust particles etc. A breather vent in the drive allows for any large and sudden changes in atmospheric pressure.

THE ACORN AND WATFORD UPGRADES

These are the two most popular upgrades for the 300 series, and both consist of an internally mounted 20Mbyte 3.5" hard drive, and a podule carrying the hard disc controller. When installing either, it will be necessary to add a podule backplane and cooling fan to the Archimedes.

The fitting of both upgrades is relatively straightforward. The podule is a half-width unit, and unless it is fitted next to an existing podule, it will be necessary to use the blanking plate and joiner provided with the upgrade. The drive itself is then mounted next to the existing floppy. On the Acorn system a 'U' shaped bracket holds the drive in place, while the Watford drive uses two angle brackets. In both cases fitting involves only the insertion of a few screws. Once the drive has been mounted, it must be connected up. There are two ribbon cables between the podule and the drive, and a power cable which is already present in the computer. Connecting these is simple. With the Acorn upgrade you must also fit the 'Hard Disc' LED to the front panel and change the front sticker. The Watford unit does not have any drive in-use indicator - no great loss really.

Table 1. Disc operation speed (All values in seconds)

OperationFloppyAcorn Watford
Screensave (80K)4.580.520.51
Screenload (80K)3.370.330.32
*SAVE 80K3.960.430.32
*LOAD 80K3.370.340.29
PCW Store Benchmark2.991.431.19

DRIVE SPEED

With all hard disc upgrades being identical in terms of software, all that there really is to choose between them is access speed, price, noise and reliability. Table 1 shows the timings for a number of practical disc operations for the Acorn and Watford systems, and a floppy for comparison. The store benchmark involves writing a number of strings using PRINT#.

DOCUMENTATION

The watford documentation consists of a few pieces of A5 paper stapled together. This 'manual' gives instructions for fitting, and also shows how the podule can be used to connect an external drive instead of the internal unit. The Acorn system is classed as a dealer only upgrade, and is supplied with no documentation at all. To this end, the Acorn system is even supplied without a formatter program, this being up to the dealer to supply.

ACORN VERSUS WATFORD

We have already said that both upgrades are identical in terms of software, and as can be seen from the table, there is little difference in speed. One area where the two drives do differ is in terms of noise. Both have a similar background noise (about the same as produced by the fan), but the track-to-track stepping of the Watford unit is more 'clonky' than the Acorn one. It is too early to comment on the reliability of either system. Another plus feature of the Acorn upgrade is the ability to add a second drive to the controller by soldering a connector to the board and mounting the drive externally. However, the main area of difference is the price - £435 for the Watford system and £567 for Acorn's. You may feel that it is worth paying an extra £132 for a slightly quieter drive and the ability to add a second drive, but most users, given the choice, would probably opt for the Watford system.
ProductWatford Electronics 20Mbyte hard disc & Controller
SupplierWatford Electronics,
 250 High Street,
 Watford WD1 2AN.
Price£435.85 (inc. VAT)
ProductAcorn 20Mbyte hard disc & Controller
SupplierAcorn Computers,
 Fulbourn Road,
 Cherry Hinton,
 Cambridge CB1 4JN.
Price£567.74 (inc. VAT)

CARE OF HARD DISCS

Because a hard drive is hidden away inside the computer, there is a great tendency to forget all about it. To an extent this is a reasonable stance to take, as hard drives require no routine maintenance, cleaning or the like. However, hard drives are very fragile and must be treated with the utmost respect when they are handled. Before turning off the computer, the hard drive must be parked with the command *BYE (or *DISMOUNT). This moves the head to a safe landing track because as soon as the drive is powered down the air flow will stop and the head will crash against the disc. If this was to occur on a track containing data, then it is possible that the data would be corrupted, and the drive need reformatting. On a similar note, a computer fitted with a hard drive should never be moved unless the heads are parked and the computer turned off. Additionally, sudden jolts and knocks should be avoided. You should not remove the drive from the computer unless really necessary, and you should NEVER attempt to dismantle a hard drive, as this will invariably ruin it.

ORGANISING A HARD DISC

When most people fit a hard disc, the first thing they do is to copy all their most used floppies onto it. This can very quickly lead to utter chaos in disc organisation, and make finding a particular file a nightmare. Even if each individual floppy contained a perfectly logical directory structure, when over twenty such discs are combined the logic can soon break down.

One simple solution that can be adopted when transferring n floppies to a hard disc is to create n directories in the root of the hard disc, and copy the contents of each floppy directly into these directories. This will mean that the structure is maintained exactly as before, but with all the files accessible at all times. A much better solution though is to create a number of sub-directories according to different type of programs. For example, you could have a directory for Basic programs, one for C programs, a word processing directory etc.