Hard to believe that only a few decades ago computer programmers literally punched cards to tell computers what to do. It was interface and data storage in a slim, portable, recyclable form — cardboard.

Of course, computer hard drives today — even consumer models — make punch cards a punchline. Moderately sized computer hard drives hold hundreds of gigabytes, and there's even a terabyte (1,024 gigabyte) drive out there. Shrinking hard drive cost and size means stable, high-speed hard drives are working their way into portable electronics like video cameras. Now even laptop hard drives can seem cavernous.

Covered in this guide to computer hard drives:

1. How much is enough memory in your hard drive
2. Understanding hard drive technical specs
3. Why laptop hard drives are big enough to compete
4. Backing up to external hard drives

Action Steps for Shopping for Hard Drives
The best contacts and resources to help you get it done

First cut on hard drive selection is sheer size

A gigabyte used to seem like a lot of space, but no longer. If you expect to store a mountain of digital photos, MP3 music files or edit home video, you'll need gigs to spare.

I recommend: For an entry level PC now, 80GB is considered normal. A gaming and entertainment PC might come with as much as 500GB, a half terabyte. Some well-known makers of hard drives for laptop and desktop systems, as well as external hard drives, include Hitachi America, Western Digital, Seagate, IBM, CMS Products, Dell and HP. For permanent storage of large amounts of data, consider external hard drives like a CD or DVD burner or CD and DVD drives.

A look at hard drives from a technical standpoint

Speed, cache, buffer, ATA, SATA, RAID ... there's a lot of terminology. If you buy a notebook or PC already built, it will likely come with the appropriate drive installed. But if you are replacing laptop hard drives or building a PC from scratch, better read up first.

I recommend: There are good, short guides to hard drive terms and technical explanations at Vunet, PC World and CNET.

Laptop hard drives are all grown up -- because they have to be

Computer makers were famous for cutting corners on portable computers to drive down price. Now that people increasingly replace desktops at home with sleeker, easier-to-store laptops, hard drives inside them have had to keep up.

I recommend: If your notebook is due for an upgrade, probably best to just buy new and enjoy all the latest technology. Nevertheless, CNET has a video guide to upgrading laptop hard drives. For alternatives to laptop hard drives, see Business.com for more on buying a high capacity removable media drive or USB drive.

Back up your files with external hard drives

For many people, a simple metal box as thick as a stack of cards is all they need to do potentially business-saving backups. Most external hard drives come with software that triggers a copy of your entire PC every so often.

I recommend: For home or small business, see computer hard drives from Maxtor, La Cie, Seagate, Apricorn, SimpleTech, Iomega and Buffalo. See Business.com for more on external hard drives. The ultimate corporate version of the external hard drive is NAS, or network-attached storage. Take a look at this breakdown on NAS and its uses at CNET. Also, to complement your data strategy, take a look at network back up and recovery software at Business.com.

Tips & Tactics for Selecting the Hard Drive You Need

Helpful advice for making the most of this Guide

• •  Got to keep moving? Most new portable laptop hard drives are very small -- about the size of a pack of cards or less -- and connect to any computer using a USB cable.
• •  Computer hard drives are growing fast, but so are the size of operating systems and, of course, photo and music collections. Buy at least double the space you think you'll need, particularly for a notebook computer, which is harder to upgrade later.
• •  Remember, no hard drive is absolutely bombproof. If you expect to keep your important business documents or family memories forever, develop a redundant system where data is in at least two places.