by Earl Dallas: earl@dallas.freeserve.co.uk

If you do any serious work on your PC you should backup your work frequently. If you are not sure whether you need to make backups of your data just image the following scenario. You switch on your computer and the hard disk fails to start, so all data saved onto the disk has been lost. If this worries you then you need to make regular backups of your work. Modern Windows applications make backup to floppy disks impractical. The new large removable disk systems such as LS-120 and Zip are improvements in both speed and capacity, but these systems are still not suitable for multiple large files such as those generated by sound and graphics programs. Traditional tape streamers are slow and removable hard disks are expensive. A cheap alternative is a DAT tape drive - this may surprise you as DAT drives start at around £500 for new drives. I suggest that you consider a second-hand drive, which can be purchased for a fraction of the price of a new drive.

To give you some idea of the performance that you can expect from a DAT drive, 58Mb of data was saved to a hard disk, a LS-120 removable disk drive and a DAT tape drive. The results are shown below. The time taken to complete each operation is shown in brackets.

58MB	copied to hard disk at a rate of	74MB/min	(47 seconds)
58MB	verified with hard disk at a rate of	120MB/min	(29 seconds)
58MB	copied to LS-120 disk at a rate of	9.6MB/min	(6 minutes 2 seconds)
58MB	verified with LS-120 disk at a rate of	21MB/min	(2 minutes 45 seconds)
58MB	copied to DAT tape at a rate of	19.5MB/min	(2 minutes 58 seconds)
58MB	verified with DAT tape at a rate of	22.1MB/min	(2 minutes 37 seconds)

These tests show that the DAT drive is twice as fast as a LS-120 disk for data writes. They also have a capacity of 2GB compared to that of 120MB for the LS-120 disk. The price of the media and capacities of LS-120, ZIP, Iomega DITTO 2GB tape and DAT tape are give below. The pound per megabyte cost for each medium is shown in also shown.

Device	Capacity	Medium Price	Cost ( £ per MB)
ZIP disk	100MB	£10	0.1
ZIP disk	250MB	£17	0.068
LS-120	120MB	£10	0.083
DITTO	2GB	£15	0.0075
DAT	2GB (90m)	£5	0.0025

These figures show that DAT is the cheapest. Although the Ditto tape is nearly as cheap the Ditto tape drive is considerably slower.

As mentioned earlier new DAT drives start at around £500 and have capacities that start at 2GB per tape and rise to around 40GB. I purchased a 2GB drive from computer exchange (www.cex.co.uk). Check the Internet page for shop locations, current prices and availability. Computer exchange sells second hand as well as new equipment. The shop will also purchase certain computer equipment. A greater price can be obtained for unwanted computer equipment if goods are taken in exchange rather than cash.

The drive that I recently purchased is a digital TLZ07 2/4 GB DAT, (the 4GB represents the drives capacity for compressed data). I purchased the drive from the Birmingham computer exchange shop for £70. Surprisingly, the drive came with a 1 year warranty. I would usually expect 90 days for a second hand piece of equipment. For your £70 you get the bare drive, no cables, instructions or drivers. The shop had a selection of drives from various manufacturers. Most DAT drives are the correct height to fit into a PC 5¼ inch drive bay, but only some of the drives have a bracket that covers the entire drive bay width. It is worthwhile travelling to a shop to obtain a drive that will fit into your chosen enclosure. External drives already housed in an enclosure with a built in power supply may also be available but these are rarer and more expensive. DAT drives usually come with a SCSI interface, so you will need to purchase a SCSI interface card to use the drive if you do not already have one. Expect to pay £30 to £50 pounds for an interface card. Cards are available for either ISA or PCI PC card slots. All SCSI drives have some way of selecting the drive's address, usually by removable links or a bank of switches. Since you will not receive any instructions with your drive it is important that you check the drive that you purchase and ensure that the links/switches are labelled so that you can identify their function. The drive that I purchased contained a link that changed the identity of the drive. This as very useful as the software I used to control the drive did not recognise the drive as a TLZ07. However, the drive's alternative identity. "Archive Python", was recognised by the software. DAT drives look much like any other type of tape streamer, but you get two indicators instead of the usual one and an eject button. As the tape sits completely inside the drive it cannot be pulled out by gripping the back of the tape case, like a normal tape streamer cartridge. One of the two indicators illuminates when a tape is inserted and flashes while the tape is being accessed or wound. The other indicator lights when a write protected tape is inserted into the drive. DAT tapes have a write protect flap just like a floppy disk. This flap works in exactly the same way as a floppy disk, the flap is slid open to write protect the tape.

Once you have purchased your DAT drive, linked it to a SCSI interface card and connected power to the drive you are almost ready to start to use it. When you switch on your computer the SCSI card should notify you that it has found the DAT drive. When Windows starts it may say that it has found a new device and ask for a driver disk. Since you have no driver disk you will be unable to setup the device. Windows will not be able to access the drive directly and no icon will be shown for the drive. The backup software supplied with Windows is unable to detect DAT drives. Additional software, such as Novastor Nova Backup, will be required to access the DAT drive. See an earlier issue of the E-Journal (Vol. 1. No.6 Article 4) for a review of this software.

An indication of the drives performance was given earlier. Unlike some other types of tape streamer the DAT drives are virtually silent in operation. Physically, DAT drives resemble a miniature video recorder. Like a video recorder it has a rotating read/write head. Tapes are fed into the device in exactly the same way as a video cassette. DAT tapes even resemble video cassettes but are much smaller at just (73mm x 54mm x 10mm). The only maintenance required to keep the drive working reliably is to use a cleaning cassette periodically. Cleaning tapes can be purchased for around £9. The cleaning process is completely automatic and is handled by the drive without any software intervention. To clean the drive the cleaning tape is inserted into the unit. The drive detects that a cleaning tape has been inserted and the drive winds the cleaning tape through the mechanism. This removes dust and tape particles from the head and tape path. The tape is ejected once the cleaning process is complete.

I've had a DAT drive for several weeks now and can recommend them to anyone who does serious work on their computer, which needs to be backed up. Whatever method of backup medium you select make sure that it is easy and quick to use. If it isn't you will not use it regularly and your data will be at risk.