Discrete TPMs are dedicated chips that implement TPM functionality in their own tamper resistant semiconductor package. They are theoretically the most secure type of TPM because the routines implemented in hardware should be[vague] more resistant to bugs[clarification needed] versus routines implemented in software, and their packages are required to implement some tamper resistance.
Integrated TPMs are part of another chip. While they use hardware that resists software bugs, they are not required to implement tamper resistance. Intel has integrated TPMs in some of its chipsets.
Firmware TPMs are firmware-based (e.g. UEFI) solutions that run in a CPU’s trusted execution environment. Intel, AMD and Qualcomm have implemented firmware TPMs.
Hypervisor TPMs are virtual TPMs provided by and rely on hypervisors, in an isolated execution environment that is hidden from the software running inside virtual machines to secure their code from the software in the virtual machines. They can provide a security level comparable to a firmware TPM.
Software TPMs are software emulators of TPMs that run with no more protection than a regular program gets within an operating system. They depend entirely on the environment that they run in, so they provide no more security than what can be provided by the normal execution environment, and they are vulnerable to their own software bugs and attacks that are penetrating the normal execution environment – They are useful for development purposes.
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