Five Places to Find Part Info Online

Before the Internet, every electronics engineer had his or her own little library of databooks and catalogs. If you designed digital circuits, the most widely-used data books were the Texas Instruments' TTL Logic data books. These had a very distinctive yellow cover. If you were an analog designer, then you had to have a set of National Semiconductor Linear IC databooks. These had a very distinctive blue cover. (I think I still have copies of both the TI TTL databooks and the National Semiconductor Linear databooks in a box in my basement.)
Engineers were very protective of their databooks. They would print their names on them in big, bold letters, and only loan them out if they knew you and if they were sure that they'd get them back. This is an understandable degree of protectiveness, as your productivity as an engineer often depended on having component data at your fingertips.
Today, of course, all of this component data is online. With just a few clicks, you can quickly find datasheets and specifications on just about any component every manufactured.
Here are five places to get component information online:

1. Google. The first thing that I do when looking for component data is just Google the part number. Googling “national semiconductor 555,” for example, returned 247,000 results, and one of the first results was a PDF file with the LM555 data sheet on a site called AllDataSheet.Com.
2. AllDataSheet.Com. This website bills itself as “biggest online electronic component datasheets search engine.” It has more 20 million semiconductor datasheets, and adds more than 30,000 per month. If you're not sure of the part number, AllDataSheet.Com lets you search by part type (transistor, diode, capacitor, etc.), part description (i.e. “low noise op amp”) and manufacturer.
3. Distributor websites. Distributors, such as DigiKey, now have search capabilities for the parts they carry. I just searched for 2n2222 on the DigiKey website and was rewarded with 36 different results, including 2N2222 in plastic packages, metal cans, and surface-mount packages. The results included links to manufacturer datasheets. What I like about using distributor websites when searching for part info is that you know immediately if the part is available or not.
4. Octopart.Com. This website allows you to search for parts information from “thousands of manufacturers and hundreds of distributors.” Like DigiKey, Octopart has a Bill of Materials tool that lets you not only find parts information, but helps you manage all of the parts you need for a particular project.
5. Silicon Expert. An example of a product search engine with advanced capabilities is Silicon Expert. In addition to component specification data, Silicon Expert provides information such as lifecycle risk, product change notices, reference designs, and even conflict mineral compliance data. Of course, this data isn't free. A year's subscription will set you back $500.

Using these online sources is quick and easy, but you might also want to try using a “real” databook. In addition to component specifications, they also included selection guides and other application information. You can find physical copies from many used-book sellers. They are available online too. You can, for example, download the 1976 (second) edition of The TTL Data Book for Design Engineers by Texas Instruments. It's a 33.8 Mbyte download.