Il performance Rating è un numero intero che va da 1 a 5 che determina le performance del tuo computer. 1 è il peggiore e 5 è il migliore.
Il numero non andrà oltre 5 poichè indica solamente le performance per far girare Windows Vista, e non tiene in considerazione le performance in generale come fanno altri applicativi tipo PcMark di FutureMark Corp.

Sull'MSDN vengono spiegate molto bene le caratteristiche che deve avere un computer per ottenere un certo valore, riporto più avanti un pezzo di quell'articolo.

Ecco come viene valutato il mio computer, P4@3Ghz HT, 2 Gb di RAM DDR400, Sk Video Ati 9600 Pro:

NB: i valori ottenuti per Ram e Hard disk non si riferiscono solamente al quantitativo di memoria, ma soprattutto alla velocità della stessa, infatti ho 3 tipi di ram diverse, che non vanno in Dual Channel, per cui anche se è DDR400, in realtà non è velocissima.

Ed ecco l'articolo MSDN che potete trovare per intero qui:
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/winsat/winsat/winsatinfolevel1_struct.asp

Value	Meaning
1	The computer meets the minimum specification in order to run Windows Vista and Windows Server "Longhorn". The experience of running Windows Vista and Windows Server "Longhorn" on this computer will be similar to that of running Windows XP. These computers having the following minimum specification: Features Attributes Capabilities 256MB of memory None required None required Optical drive 1024 x 768 capable graphics sub-system and monitor CPU with SSE support These computers will run basic productivity software and simple games well under Windows Vista and Windows Server "Longhorn"; however, these computers are not well suited for games that use 3D hardware features. The primary limitation of these computers is the lack of system and video memory and graphics performance. These computers will not run Windows Vista and Windows Server "Longhorn" Media Center.
2	The computer can run Windows Vista and Windows Server "Longhorn" and exhibit performance and capabilities above those available with Windows XP. This is primarily driven by the presence of 512MB of memory and a more modern CPU. This computer will not run a composted desktop (Aero) by default and if a user turns this feature on it will have a dramatic impact on system performance and the ability to run other applications. These computers having the following minimum specification: Features Attributes Capabilities 512MB of memory CPU score equivalent to a 2.0Ghz P4 or a 2000+ AMD K7 or K8 CPU None required Optical drive Memory bandwidth score of 2.0GB/sec 1024 x 768 capable graphics sub-system and monitor Hard drive score of 20MB/sec aggregate 32MB of graphics memory D3D Score of 30Efps CPU with SSE2 support These computers will run basic productivity software and basic multi-media actives well under Windows Vista and Windows Server "Longhorn"; however, these computers are not well suited suited for handling high definition video, especially in MPEG-II, Windows Media or H.264 format when no dedicated hardware decode support is available. This is due to lower powered CPU’s and lower memory bandwidth. Computers with hardware accelerated video decode may handle some high definition video satisfactorily. These computers will play basic 3D games well, but is not well suited for current first person shooters and other D3D intensive high frame rate games. These computers will not run Windows Vista and Windows Server "Longhorn" Media Center.
3	The computer meets the minimum Windows Vista and Windows Server "Longhorn" capability requirements for the silver logo. These computers having the following minimum specification: Features Attributes Capabilities 512MB of memory CPU score equivalent to a 2.8Ghz P4 or a 2800+ AMD K7 or K8 CPU 24FPS 720P WM high definition glitch free capable DVD optical drive Memory bandwidth score of 2.5GB/sec Glitch free high definition audio hardware 1280 x 1024 capable graphics sub-system and monitor Hard drive score of 40MB/sec aggregate 64MB of graphics memory D3D Score of 60Efps Vertex/Pixel shader 2 capable hardware (DX9 support in hardware) CPU with SSE2 support These computers should play high definition Windows Media Video and MPEG-II high definition video acceptably, though this will probably use large amounts of the computer’s CPU cycles and memory bandwidth (unless hardware accelerated video decode is available on the computer). These computers will play 3D games well and is suitable for the mid-range first person shooters and other D3D intensive higher frame rate games. These computers should run Aero Express well; however, they will probably not run Aero Glass well. These computers will not run Windows Vista and Windows Server "Longhorn" Media Center.
4	The computer meets the minimum Windows Vista and Windows Server "Longhorn" capability requirements in order to run with Aero on by default. Both silver and gold logo computers should be able to meet these requirements. These computers having the following minimum specification: Features Attributes Capabilities 512MB of memory CPU score equivalent to a 3.2Ghz P4 or a 3200+ AMD K7 or K8 CPU 60FPS 1080i WM high definition glitch free