Q. I have a digital camera and use AOL as my Internet service provider. What guidelines can you give me on the size of image files?

A. When you retrieve images from a digital camera, you must think about what you're going to do with your pictures.

Many folks manage their images with a program called PhotoShop. If you want to print out your pictures with a photo-quality printer, use PhotoShop to save the image in high resolution. This will take up tons of disk space, but the file will be sitting on your own hard drive, so it is of minor concern to you.

It's a different story if, as our writer does, you want to send photos to friends via AOL or another provider. AOL has limits on the size of the files you can send. If you are sending to other AOL users, you may have a file as large as 16 megabytes. But if you are sending outside of the AOL community, you are limited to 3 megabytes.

In that case, use PhotoShop to save the images in low resolution and as .JPG (Joint Photographic Group) files. Avoid saving them as .BMP (bitmapped) files, because those are too large.

On the air, you talked about backing up on the Internet. What did you mean?

Computer users have long used floppy drives to make backup copies of their files.

So when Steve Jobs and Apple Computer produced the iMac without a floppy drive, it created quite a stir. Even the standard-bearer of tradition, IBM, has offered some Aptiva models without the benefit of floppy drives.

The statement these computers make is: Why bother keeping a lot of data stored on disks in your desk drawers when you've got a good-size hard drive, and the real action is out on the Internet? But you still may ask, "How do they expect us to make backups of our files?"

I was pointing out that there is a way to do so on the Web. Sites such as SwapDrive.com and NetFloppy.com offer to store your documents--securely and for free--for retrieval any time and from any place you can log on. The sites don't charge anything because they make their money by selling advertising.

Personally, I make my copies on a Zip drive and keep a copy at work and a copy at home. But imagine if you were on the road and spent the entire day entering data. Being able to dump all that information safely on a remote site would certainly give you insurance against a hard-drive failure--and help you sleep more easily.

I am concerned about memory cards that are used in digital cameras. Are they affected by the X-ray equipment at airports?

No. Memory cards for digital cameras are all designed to withstand X-rays at airports.

A bit of history: The memory cards used in the more expensive camera models have their source in a standard developed by a group called the Personal Computer Memory Card International Association (PCMCIA).

Eons ago, when memory for personal computers was very expensive, one proposed solution was to manufacture memory on credit-card-size devices. The standard, while little used for desktops, became popular for modems and network cards in notebook computers. Although the association always called the device a PC card, it became popularly known as a PCMCIA card.

There are other kinds of memory cards for digital cameras, including Compact Flash and SmartMedia. No problem with any of these when it comes to airport security machines.

John Gilroy of Item Inc. is heard on WAMU-FM radio's "The Computer Guys" at 1 p.m. on the first Tuesday of the month. Send your questions to him in care of The Washington Post, 1150 15th St. NW, Washington, D.C. 20071-5302 or via e-mail at jgilroy@iteminc.com.