indicates the number of data transfers across the bus during each 66 MHz clock cycle. Such transfers use source synchronous clocking with a "strobe" signal (AD_STB[0], AD_STB[1], and SB_STB) generated by the data source. AGP 4× adds complementary strobe signals. Because AGP transactions may be as short as two transfers, at AGP 4× and 8× speeds it is possible for a request to complete in the middle of a clock cycle. In such a case, the cycle is padded with dummy data transfers (with the C/BE# byte enable lines held deasserted). Connector pinout The AGP connector contains almost all PCI signals, plus several additions. The connector has 66 contacts on each side, although 4 are removed for each keying notch. Pin 1 is closest to the I/O bracket, and the B and A sides are as in the table, looking down at the motherboard connector. Contacts are spaced at 1 mm intervals, however they are arranged in two staggered vertical rows so that there is 2 mm space between pins in each row. Odd-numbered A-side contacts, and even-numbered B-side contacts are in the lower row (1.0 to 3.5 mm from the card edge). The others are in the upper row (3.7 to 6.0 mm from the card edge). PCI signals omitted are: The −12 V supply The third and fourth interrupt requests (INTC#, INTD#) The JTAG pins (TRST#, TCK, TMS, TDI, TDO) The SMBus pins (SMBCLK, SMBDAT) The IDSEL pin; an AGP card connects AD[16] to IDSEL internally The 64-bit extension (REQ64#, ACK64#) and 66 MHz (M66EN) pins The LOCK# pin for locked transaction support Signals added are: Data strobes AD_STB[1:0] (and AD_STB[1:0]# in AGP 2.0) The sideband address bus SBA[7:0] and SB_STB (and SB_STB# in AGP 2.0) The ST[2:0] status signals USB+ and USB− (and OVERCNT# in AGP 2.0) The PIPE# signal (removed in AGP 3.0 for 0.8 V signaling) The RBF# signal The TYPEDET#, Vregcg and Vreggc pins (AGP 2.0 for 1.5V signaling) The DBI_HI and DBI_LO signals (AGP 3.0 for 0.8 V signaling only) The GC_DET# and MB_DET# pins (AGP 3.0 for 0.8V signaling) The WBF# signal (AGP 3.0 fast write extension) See also List of device bandwidths Serial Digital Video Out for ADD DVI adapter cards AGP Inline Memory Module Notes References External links Archived AGP Implementors Forum AGP specifications: 1.0, 2.0, 3.0, Pro 1.0, Pro 1.1a AGP Compatibility For Sticklers AGP pinout AGP expansion slots