Straight Talking

I have shelved my planned column for this month, to bring you a couple of urgent health warnings. If you are buying a new PC or a new CD-ROM drive, or both, there are two important features to look for if you want to guard against obsolescence. The PC should have USB sockets on the rear.

The CD-ROM drive should be of Multiread standard.

USB, the Universal Serial Bus, is a standard agreed by Intel, Microsoft, Digital, Compaq, NEC, IBM and Philips and backed by over 300 other companies.

It lets up to 127 peripheral devices plug into a PC, in daisy-chain fashion, with "hot plug and play".

The Windows OS works with a chip on the mother-board to detect each device as it is connected, load the software driver and provide control access without the need to juggle IRQ/DMA settings.

So there are no conflicts. Devices can be plugged in and out while the PC is running. There is no need to re-boot between connections.

The devices can be a mouse, keyboard, monitor, scanner, joystick and printer, with data transfer rates of up to 6Mb/sec per device. A single socket on the PC feeds a hub which has four sockets: three of these connect to separate devices and the fourth connects to another hub, which has another four sockets, of which one connects to another hub and another three connect to more devices, and so on up to a total of 127 devices.

USB also rewrites the rules for hi-fi on a PC. With conventional sound-card systems, the digital audio is converted into analogue stereo and amplified inside the PC, and then fed out to the loudspeakers. The high-frequency digital hash that envelopes the motherboard adds buzzing noises to any low-level signal, so even the best sound cards produce sound which is poor by hi-fi standards. USB carries the sound out to the speakers in digital code. The speaker contains its own digital-to-audio convertor and amplifier.

Around mid-1996 Intel started putting USB control chips on all the motherboards it makes for PC manufacturers. In some cases these chips are not connected: there is no socket on the chassis. This is clearly an absurd situation.

The sockets put a few pence on the factory cost, but anyone with a socketless PC must pay a disproportionately high price for an authorised service agent to retro-fit them. Often, the owner will not even know there is a USB chip on the board.

It should be possible to add an adaptor card to a PC, which converts it to USB operation, but it will need its own configuration so the motherboard solution will be far easier. Of course, USB will only work with new devices, which are USB-ready. I don't doubt the promises for USB will turn out to be overblown. Nothing in the Windows world is ever that easy. But I would not now dream of buying a new PC unless it had a working USB connector on the rear of the chassis. Likewise I would not now dream of buying a CD-ROM drive, unless it carried the magic word "multiread". So just as dealers will be busy flogging off non-USB PCs, you can be sure that they will now be off-loading non-Multiread ROM drives to unwary customers.

Hewlett-Packard, Mitsubishi, Philips, Ricoh, Sony and Yamaha have agreed a standard for CD-ReWritable. CD-RW discs record, play back and erase on CD-RW recorders. They also play back on a new generation of CD-ROM drives. Unknown to owners, some have purchased CD-ROM drives which contain "multiread" circuitry which self-adjusts for CD-RW playback.

The CD-RW discs work on the phase change principle. CD-RWs don't need a protective caddy and can fit any conventional CD drive. CD-audio players and CD-ROM drives have a light sensor designed to read pressed or write-once discs which reflect 70 percent of the laser light from the lands between the data pits, and around 30 percent from the pits. It's possible to make a phase change alloy matching these optical characteristics, but the recording laser has to be powerful to melt the alloy. The system is then too expensive for consumer use.

Six months ago Philips and HP agreed a standard for CD-RW with 20 percent reflection from the alloy in its crystalline state and five percent in amorphous state. The recorder can use an inexpensive laser, but the player must have a more sensitive sensor, so the CD-RW standard also defines a Multiread player with automatic gain control in the circuit which amplifies the signal from the light sensor. If the disc is a pressed CD or CD-R, the amplifier gain is turned down; if the disc is a CD-RW with lower reflection, the gain automatically increases.

The Multiread standard has now been endorsed by all the major manufacturers of CD-ROM drives. Around one third of the latest models in the shops, known as 12-speed drives which run at 12 times normal speed, already have AGC. Once makers have sold off their old stock, all new drives will conform.

Don't buy the old stock unless you do not want to play CD-RWs.

Barry Fox is at 100131.201@CompuServe.COM.

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