Xerox Alto I Hardware Manual page 31

Alto Hardware Manual Section 3: Emulator
25
XMLDA
XMSTA
TIMING DETAILS
The microcode has roughly the following speed characteristics:
Horizontally, along one raster line (so to speak):
store constant
move block
if skew not zero
if source not zero
1st or last word
function not store
13 cycles/word
23 cycles/word
add 6
add 7
add 13
add 6.
Vertical loop overhead (time to change· raster lines):
14-21 cycles/scanline, depending on source/dest alignment
add 6 if function uses gray
Initial setup overhead (time to start or resume from interrupt):
approximately 240 cycles
Total for a typical character, 8 wide by 14 high:
approximately 1500 cycles
These timings all in units of Alto microinstruction cycles and, do include all memory wait time
and do not include any degradation due to competing tasks, such as the display or disk. For
typical characters on the Alto screen, BITBLT is about 2/3 the speed of CONVERT.
61025B Extended Memory Load Accumulator (Alto II only)
Loads ACO from the location addressed by ACI in the alternate bank.'
61026B Extended Memory Store Accumulator (Alto II only)
Stores ACO into the location addressed by Acl in the alternate bank. If the the addressed bank
of memory has not been installed, the instruction yields undefined results and will probably
cause a .parity error. See section 2.3.