Minecraft – the difference between using the Pattern Grid and using the Processing Pattern Encoder in Refined Storage

I'd say that the most major difference is the addition of the Thaumcraft and Mystcraft mods in Technic. As others have said, Tekkit is for use in a multiplayer setting, while Technic is for SSP only.

The major mods in both are IndustrialCraft2 (adds electricity and industrial machines), Equivalent Exchange 2 (adds in alchemy using the Philosopher's Stone, and several highly powerful end-game tools like the Void Ring, Ring of Arcana, etc), Redpower 2 (adds in redstone wiring and machines), and Buildcraft (adds in some automated mining machines as well as transport tubes and controls for that).

In addition to those core mods shared by both packs, Technic adds several features that are best in singleplayer. Major differences are:

• Thaumcraft / Thaumcraft 2: Thaumcraft is a magic and arcana inspired mod for Minecraft. It features aura and vis (pronounced "vees"), which introduces a new mechanic for enchanting and crafting unique items. Thaumcraft also introduces the "Taint" - if you've ever played Terraria, the Corruption from that game is similar to the Taint in Thaumcraft.
• MystCraft: MystCraft is a mod for Minecraft inspired by the Myst series of video games. It allows the player to craft different types of books which allow for teleportation between different "ages", which are basically new worlds. As you get more advanced, you can write your own books, which lets you customize the ages to your liking. For instance, I wrote an age with the "Hell" modifier, which spawned me in a world with a ton of Eldritch Obelisks (artifacts of great power in Thaumcraft), which helped me to get ahead on my research.

A few other minor changes worth mentioning:

• Somnia: Simulates the world while you're sleeping. So, unlike vanilla Minecraft, when you sleep, stuff smelts, crops grow, etc.
• Mo' Creatures: Basically what it says on the tin. There's a ton more creatures in Technic than there are in regular Minecraft.
• Treecapitator: Handy little mod so that, if you chop the bottom of a tree out with an ax, all the wood in the tree falls down at once (kind of like real life, eh?).

The normal minecraft loader downloads what's called Vanilla Minecraft, what is developed and released by Mojang. Tekkit is a collection of mods which change and add features to Minecraft - using their loader is easier than using ModLoader and messing with your jar files. The launcher also loads different mods such as YogBox, Hack/Mine and Voltz.

There are two different versions of Tekkit, Tekkit Lite and Tekkit Classic. Classic is the older version and Lite is the newer version that is aimed at smaller versions. The differences between them appear quite small - for the list of mods in them please see this link on the Tekkit site.

Using Mods can add a lot of depth to the game. You will need to learn fairly quickly a lot of new crafting recipies or how things work and connect together, especially with the inclusion of IndustralCraft2.