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Article from Music Technology, May 1994

Taking the hard option... everything you need to know about hard disks - and then some. Ian Waugh is your guide.

Once a luxury of only professional computer users, hard disk drives are now included with every machine sold. But how much disk space do you need? How fast does your data need to flow? How much need you spend? Answering all these questions - and more - Ian Waugh...

It's true. Personal computers are really powerful these days; compact and expandable, even a relatively inexpensive machine can provide you with a computing power approaching that of Harlow in Essex. A computer of equivalent power 15 years ago would have taken a large warehouseman to hold it... Really.

Given that computers are getting more and more powerful, you might think that speed is not the problem it used to be. But modern applications are growing in size, too, becoming more sophisticated and graphics-orientated and demanding a fast machine in order to work at a reasonable pace. Speed is also essential for any process based on the rapid transfer of data such as direct-to-disk recording and video playback.

All of which puts an added burden on your computer's hard disk drive. Simply put, if you don't have the disk space to install that new multimedia program or the drive speed to transfer data at the required rate for that direct-to-disk recording system - you're stuffed. In fact, hard disks are probably one of the most underrated items in your computer setup. This feature will tell you a little bit about them and help you select a suitable disk when buying a new computer or if you're looking to upgrade your old one.

In the early days of hard disks, 10Mb was a lot of space, more than enough to install several applications and store their data. The minimum size disk you're likely to find for a PC or Mac now is 40Mb although in reality this is far too small for a modern computer system. Many suppliers are currently suggesting a minimum of 80Mb or 100Mb and some even recommend 250Mb drives.

OK, the smaller disks are not going to be too small for everyone. If you only want to run one application such as a wordprocessor fine, but if you're involved in direct-to-disk recording, sequencing, multimedia, CD-ROMs, DTP; if you're likely to add even two or three new applications to your computer over the next few months; if you install the odd game, enjoy Shareware and the programs given away on the covers of magazines - then that 'massive' 100Mb of disk space will vanish in no time at all.

Large capacity hard disks are particularly important for direct-to-disk recording and multimedia. They are useful, too, for storing and organising samples although a removable hard disk is generally a better option here.

To give you an example of how much disk space a computer can gobble up, the System folder on my Mac contains 30Mb of data and the Windows directory on my PC contains over 25Mb of files. My PC's 230Mb hard disk has been full for three months and I've only had it for a year. Time for me to upgrade. I was wise with my Mac and have a total of 1Gb of hard disk space divided between the internal and an external drive. Currently half of this is free. I have a 30Mb drive on my ST which has been far too small for at least three years, but such is the current ST market that I'm not inclined to upgrade it. ST applications don't need as much disk space as those for the Mac and PC and ST drives are horrendously expensive.

The first thing you must do is budget for a hard disk which will see you through, hopefully, a couple of years at least. Always overestimate - it'll be cheaper in the long term. The good news is the cost of hard disks is falling. More good news is that the bigger the disk you buy, the faster it's likely to be and the cheaper each megabyte of storage space will be. For example, a 40Mb disk for the Mac or PC is likely to cost around £2 per megabyte whereas a 1Gb drive could work out 75p or 80p per megabyte. Opt for a 2Gb drive and prices can be as low as 60p per megabyte. A typical 40-52Mb drive for the ST will cost between £150 and £200. When you start looking at 500Mb and 1Gb drives the prices get better but still cost over £1 per megabyte.

A 52Mb SCSI 2 drive for the Falcon could cost £250 although why anyone would want such a small drive for the Falcon is anyone's guess - unless they bought the hard disk-less Falcon which I can only suggest borders on folly. A 540Mb drive would be much more sensible and at around £600, more reasonable, too.

Apart from size the other vital consideration is speed. Before buying any hard disk drive, you need to know its access time (sometimes called the seek time) which is the time it takes the drive to reach a certain part of the disk, and the data transfer rate (DTR) which is how much data the drive can shift in a given time. Access time is quoted in milliseconds (ms) and while 30ms was once considered fast, most modern PC and Mac drives have an access time of 19ms or less and some large drives are as fast as 10ms. 19ms is the minimum speed required by most direct-to-disk recording software but if you are working with digital video and want your drive to read graphics data you need the fastest you can get. And then some.

The data transfer rate, DTR, is measured in Kb/sec or Mb/sec and is a measure of how quickly the drive can deliver the data to the computer. Manufacturers usually quote a maximum theoretical rate, though in practise the computer is likely to produce a bottleneck or two which can slow down the transfer rate dramatically. A typical DTR for a PC system may be around 1-1.5Mb/sec although this can be improved considerably using more efficient data buses such as Intel's new PCI bus, Vesa or SCSI 2. A good caching system will also boost throughput. For most applications the DTR isn't critical, but if you are trying to read and play audio or video from disk, it is. In fact, both these applications really need specialised hardware - especially video work.

So having decided on the size and speed of disk you need, how easy is it to buy a new one and connect it? We'll tackle ST and Falcon hard disks first as these are fairly easy to install. Most drives come ready to plug in and go. The ST cannot be connected directly to a hard disk so make sure you get all the necessary cables. You'll also need a formatting utility which should come with the drive.

If you're not considering upgrading your ST to another computer and think you'll still be using it for the next couple of years, a hard disk is an excellent investment. It will speed up your work enormously and you'll wonder how on earth you managed without one.

A typical Mac formatting utility with easy format options.

Mac are also easy computers to add hard disks too. They use SCSI drives and, like all things Mac, you can usually buy one, plug it in, format it and go. One of the benefits of SCSI is that you can add several drives and get them to work together fairly painlessly.

PC hard disks, as you might expect, are several degrees more complex. Most PCs use an IDE drive (see Jargon buster). The maximum IDE drive size is about 500Mb so if you want to increase your storage capacity you'll have to install a SCSI drive or add another IDE drive. Unlike SCSI, IDE only supports a maximum of two drives and they must be configured as Master and Slave. However, wouldn't you know it, some drives just won't work together. The only way to discover if they will is to read the documentation thoroughly and/or contact the supplier/manufacturer and ask them.

MS-DOS has a built-in cache called Smart Drive which will increase data throughput.

IDE drives are supported by the PC's BIOS (see Jargon buster) and you have to run the Setup program to tell your system it has a new drive. If you have an old BIOS it may not support a large hard disk. Something else to check. If you plumb for a SCSI drive you'll need a SCSI interface which can cost around £100 although it will support up to seven devices. SCSI devices are driven from software and you'll have to copy some files onto your system to take care of this.

If you're in any way unsure about upgrading your PC drive, ask a specialist or arrange for the dealer to install the drive for you. And make sure you back up all your data first. If you haven't yet bought a computer it makes sense to spend a bit more to get a hard disk which will last you for a few years and which is fast enough for any audio or video work you want to do. And once you've got a suitable hard disk, you need to look after it so check out the Hard Disk Problems - Prevention and Cure section of this feature.

The case for compression

If you're running short of disk space you may be wondering whether to buy another disk or save some money and invest in a compression utility. Programs such as DOS 6's DoubleSpace and Novell's Stacker for the PC, and Disk Doubler for the Mac will compress both applications and data files on the fly, effectively increasing your disk's storage capacity. They often claim to double your disk space but in practice the savings are somewhat less, although still significant.

The advantage of these programs is that they are easy to install and they work in the background. However, there are two potential dangers you should be aware of. Although the programs compress and decompress fairly quickly, you will undoubtedly experience a noticeable delay, especially on slower machines. The second problem involves data security. It's just possible for disaster to visit your computer while the program is in the middle of doing its stuff. If this happens you could lose data and find it hard to recover because of the way it has been compressed. You should, of course, always back up your data regularly, but if you use a compressor this is especially good advice.

There are probably thousands of people using compressors quite happily but on a purely personal note I'd rather invest in a second or larger hard disk than slow down my computers and run the risk of losing data.

Caching the bus

The Mac's Memory Control Panel has a disk cache option.

All computer systems use buses and virtually all hard disk systems employ some form of caching but the PC excels in making a relatively simple concept more complex than the Maastricht Treaty. Here's a very brief summary of the situation. Stick with it and don't let the acronyms throw you...

Simply put, a bus is a set of wires which carries data from one part of the computer system to another, say between the computer's main processor and the disk drive or the monitor. The traditional PC bus is the ISA (Industry Standard Architecture) bus with a DTR of around 1-1.5Mb/sec but faster computer systems demand a bus which can carry more data more quickly in order to avoid a bottleneck - so other buses appeared such as EISA (Extended ISA) and IBM's MCA (Micro Channel Architecture) which can be up to five times faster.

In order to speed up data transfer even more, systems employ a cache or buffer. In a hard disk, for example, this would 'anticipate' the data the computer is going to request next and store it in special area of memory - the cache. The computer can read data far more quickly from memory than it can from the physical disk so data throughput is increased. PC systems have a built-in cache in the form of Smart Drive although on-disk caches are usually far more efficient.

Then along came the local bus, designed to offer greatly increased data throughput by communicating more directly with the computer's processor. There are two prevalent standards - the Vesa (Video Electronics Standard Association) VL-Bus (also knows as the Vesa Local Bus) and Intel's PCI (Peripheral Component Interconnect). The Vesa bus got there first, it's relatively cheap and currently has more support than PCI, but it's not as tight a standard. It's possible that a VL-Bus from one manufacturer may not work with a VL-Bus device from another.

Current VL-Bus systems can struggle at 40MHz clock speed and simply don't work at 50MHz. A small word of warning to anyone attempting to buy a 50MHz VL-Bus system - don't! Especially from Reeves Computers which had the temerity to sell a 50MHz VL-Bus PC which quite simply wouldn't run at 50MHz! Steer well clear, folks.

The PCI bus can match the VL-Bus speed and before too long it is expected to double it. It's a newer standard so it doesn't have as much third-party support - although this will undoubtedly come. It's also a more robust and technically superior standard than Vesa which is geared towards improving video output. PCI has an eye towards multimedia and is designed with video and full-motion video applications in mind.

PCI and Vesa will be able to coexist in the same PC.

An interesting twist in the plot is that Apple has expressed an interest in using PCI in new Macs and PowerPCs. Another PCI benefit - which will probably take a year to make much of an impact - is its plug in and play ability.

A system will automatically recognise a PCI card and configure itself automatically which saves messing around with IRQ settings and the like.

To sum up - Vesa is cheaper, PCI is technically superior but costs more and it will be a while before it fully catches on.

Jargon Buster

Gb: Gigabyte or 1,024 Megabytes.

IDE: Integrated Drive Electronics. A drive with most of the controlling hardware built-in, reducing the cost of the PC controller card.

SCSI: Small Computer Systems Interface. A connection protocol used by PCs, Macs, STs and most other computer systems. SCSI devices can be daisy-chained and a SCSI interface can control up to seven devices including hard disks, CD-ROMs, scanners and so on.

SCSI 2: An enhancement to SCSI which can transfer data more quickly.

BIOS: Basic Input/Output System, a program usually stored in a PC's ROM which tests the system when it's switched on and loads the operating system, usually DOS, from disk, and generally helps the software and hardware work together.

Moving Pictures

The reason why the data transfer rate is so important in multimedia applications is because of the massive amounts of data which need to be shifted in order to display moving images on a computer screen. If you're working in true colour 24-bit graphics with only a quarter size viewing area of 320 x 240 pixels, the system would have to move about 6Mb of data per second. This is beyond the limits of an ISA bus but quite possible using one of the newer bus systems. However, a hard disk with a data throughput of 300Kb/sec certainly isn't up to the job.

If you want to produce 24-bit, fullscreen, 640 x 480 videos you're looking at shifting 22-26Mb of data per second. No drive can handle that and even if it could, how much disk space would you need for even a 5-minute short? Save your calculator's batteries - it's about 7Gb!

So, you need specialist video compression hardware (which we'll leave for another article). Interestingly, Micropolis have developed some very fast drives for the digital video market which we hope to be looking at soon (see last month's Scanners).

Incidentally, in case you were wondering, you can dramatically reduce the amount of data the system has to move by using 16-bit colour instead of 24-bit. But it doesn't look as nice.

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Virtual Reality

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The Mix

Publisher: Music Technology - Music Maker Publications (UK), Future Publishing.

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Music Technology - May 1994



Feature by Ian Waugh

Previous article in this issue:

> Virtual Reality

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