Z-buffers must meet the drift specification (Input-2-Output delay variation) required by Intel for Romley/Grantley. Renesas has many different Z-buffer versions. The 9ZX21901 shown above is the 19-output version that is based on the Intel DB1900Z Z-buffer specification. Renesas has two versions: Rev B which has tunable external feedback and Rev C with fixed external feedback. Because some applications will not need a many as 19 outputs, Renesas also has 15-output and 12-output versions available. There are two versions of the 15-output devices released to production: Rev B with tunable external feedback and Rev C with fixed external feedback. Additionally, there are two 12-output versions: The Renesas 9ZX21201AKLF is a 64-QFN device with 12-output enables, and the 9ZX21200AKLF is reduced pin count device, 56-QFN with 4-output enables. All Z-buffers share DB1900Z features such as multiple SMBus addresses and work into 100 Ω or 85 Ω differential impedances.