The price of power
How expensive is it, electricity wise, to run a computer? My wife is always chasing me to turn it off when I am not using it. Joe Phillips
country.joe@ntlworld.com
Jack Schofield replies: Personal computers don't use much power: they often have power supplies in the range 120-150watts, and probably draw less than 100watts even when working hard. A system should therefore use roughly the same as a 150watt lightbulb, including the monitor.
Most PCs nowadays meet the US government's Energy*Star 2.0 requirements, which means both PCs and monitors should switch to a low power mode after 15-30 minutes of inactivity. In low power mode, each must consume less than 30watts. Given that, in my opinion, PCs are subjected to more stress when being turned on and off than they are when left running, this suggests it is not worth turning a machine off for short periods, especially if it is being used to receive faxes and voice messages.
An increasing number of PCs do not actually turn off completely when you hit the off-switch. They have features that enable them to be "woken up" by a network message or fax or whatever, so even when they are off they take a trickle of electricity. This also applies to other devices including some answering machines, satellite receivers and VCRs. If you really want to turn them off, you have to pull the plug.
Any power transformer plugged into a wall socket is probably consuming electricity as well.
Shelter from the storm
After a violent thunderstorm the other night the modem on my iMac ceased to function. Can lightning cause this sort of damage to a computer and if so how can I prevent it? Iain Noble
Iain.Noble@tees.ac.uk
JS: Modems and personal computers, with parts usually designed to operate on 12v or lower voltages and small currents, can certainly have their chips fried by lightning, and by unexpected surges in mains power supplies. However, it is hard to know how often this happens.
Fortunately it is cheap to protect a PC and modem using surge suppressors supplied by companies such as Belkin and APC (American Power Conversion), and sold by The NetShop, Action Computer Supplies and similar outlets. Surge protectors look like multiway power adapters, but bigger. Some also protect your telephone, fax, modem, TV and satellite lines, such as the Belkin SurgeMaster 5-way 2m (£14.99 plus VAT from Action). APC also sells the ProtectNet range of devices designed to protect various kinds of data line. The Apptel2, for example, will protect two phone lines (£14.40 plus VAT from The NetShop).
Suppliers may also offer "connected equipment warranties" of up to £10,000: it varies according to what size spike the device is designed to withstand. If your equipment is fried, this should cover the cost of replacement.
Size matters
What are the advantages/ disadvantages of different image formats? I have bought a scanner, and when saving an image I am offered a bewildering choice. I scan mostly black & white line drawings and have found that a TIF format produces a much larger file than BMP, but the saved images appear to be as good as each other. Jack Freeman
jack.freeman@ukgateway.net
JS: If you don't own the original, save the biggest file you can, preferably in the TIFF (Tagged Image File Format), and store them on CD-R or CD-RW discs. TIFF is horribly complicated but the closest we have to a publishing industry standard.
You can also save and/or convert images to the JPEG (Joint Photographic Experts Group) format for viewing and general use. JPEG (.jpg) files are "lossy", ie information is lost when you convert to the compressed JPEG format.
However, you can adjust the file to be as big or as small as you like, depending on how much information you are willing to sacrifice. (Once it has gone, of course, you can't get it back.)
CompuServe's GIF (Graphics Interchange Format), which is limited to 256 colours, has fallen out of favour recently, but it is better than JPEG for some purposes, and one may be drawings. You will have to experiment to find out.
GIF is supposed to be replaced by PNG (Portable Network Graphics), a standard backed by the World Wide Web Consortium. It is a lossless system, and not much used. See www.w3.org/Graphics/PNG and www.libpng.org/pub/png for more details.
Finally, BMP is the Windows Bit Map format. It produces huge files and I cannot see any reason for using it.
Which address?
I don't want to have to dial in through different ISPs specific to reach my preferred email address, I want the convenience of sending messages from different email addresses while connecting through only one ISP only. Is this too much to hope for? Roddy Forrest
roddy.forrest@ntlworld.com
JS: Yes, it is. Nowadays most Internet service providers (ISPs) will not let you send email if you are not logged on to their service, to help prevent "spamming" (mass commercial e-mailings). If they let you come in from another ISP, you could be anybody....
Extension
One of the students on the public introduction to Java course that I run came up with another solution to creating .Java files: simply put the file name in double quotes when using Save As in Notepad.
Also, cheap and user-friendly alternatives to Notepad include editors such as Textpad, which does syntax highlighting, and environments such as Elixir.
Dr Tom Sharpe
tom.sharpe@man.ac.uk
JS: Several readers wrote in to point out that using quote marks works. And it does, as long as you remember to do it!
Another way
Someone asked how to find out what programs Windows 95/98 was running in memory and how to stop them loading if necessary. The solution you offered didn't include the option to type in "msconfig" at the Run prompt. This command brings up a huge list of options for starting Windows , the last section of which specifies what programs will load up and sit in your in-tray. To get rid of troublesome memory-resident programs all you have to do is untick the relevant box. Niall Leonard
niall@codology.com
JS: Many thanks to all the readers who wrote in to point this out: I had forgotten that msconfig included a Start-up page. The drawback is that msconfig arrived with Windows 98, and is not included in all versions of Windows.
