"This updater will ONLY update TechTool Pro 4.5.1, 4.5.2 to version 4.5.3. If you are an owner of version 4.1.2 or earlier of TechTool Pro 4, you will need to purchase the TechTool Pro 4.5.3 DVD Update.

Owners of version 4.5.1 or 4.5.2 of TechTool Pro will not need to update to version 4.5.3 unless they have acquired a new Mac model that is not fully supported by the earlier version of the program. The version 4.5.3 DVD will boot the latest MacBook Pro's as well as previous Intel and Tiger compatible PowerPC Macs. Current owners of TechTool Pro 4 can purchase the TechTool Pro 4.5.3 DVD Update for $25. Micromat also offers an Annual Subscription Service for $99. This is geared to owners of TechTool Pro 4 who wish to receive each update or upgrade automatically on DVD as soon as it is released."