from system memory to structure memory or from structure memory to system memory the host must compensate for this difference structure memory is byte addressable from the host but only longword addressable by the rendering processor 36 in unpacked byte format a bitmap contains pixels that are 8 or fewer bits deep and each pixel is contained aligned to bit zero in a byte of memory a byte contains exactly one pixel consecutive pixels on a scanline left to right are contained in consecutive bytes of memory the memory used to store a scanline of pixels is longword padded in unpacked longword format a bitmap contains pixels that are 32 or fewer bits deep and each pixel is contained aligned to bit zero in a longword of memory a longword contains exactly one pixel consecutive pixels on a scanline left to right are contained in consecutive longwords of memory a pitch is a value that specifies the relative memory location of data for pixels that are geometrically adjacent pixel data may be adjacent in x y or z pixel data adjacent in x is stored in adjacent memory locations but pixel data adjacent in the other dimensions are in remote memory locations by the amount specified by either the y pitch or z pitch pitch values may be calculated from bitmap dimensions and format pitch values.