O que é o “Boot Seguro” no Windows? já explica o que é (há um breve writeup na Wikipedia também). Em resumo:
Windows 8 supports a feature of the UEFI specification known as "Secure boot", which uses a public-key infrastructure to verify the integrity of the operating system and prevent unauthorized programs such as bootkits from infecting the device.
A descrição oficial do Boot medido é o seguinte:
As antimalware (AM) software has become better and better at detecting runtime malware, attackers are also becoming better at creating rootkits that can hide from detection. Detecting malware that starts early in the boot cycle is a challenge that most AM vendors address diligently. Typically, they create system hacks that are not supported by the host operating system and can actually result in placing the computer in an unstable state. Up to this point, Windows has not provided a good way for AM to detect and resolve these early boot threats. Windows 8 introduces a new feature called Measured Boot, which measures each component, from firmware up through the boot start drivers, stores those measurements in the Trusted Platform Module (TPM) on the machine, and then makes available a log that can be tested remotely to verify the boot state of the client.
Portanto, o Boot medido é destinado a fornecedores de antimalware e não a usuários finais. Se o seu sistema suportar (UEFI), você poderá usar o Secure Boot.