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problem can be overcome by the use of larger RAM 
boards or Real-Time-Video-Discs. RAM boards in units of 
16 Mbyte each are available and may be extended up to 
256 Mbyte (GEMSYS 35 in KERN DSP 1). There are however 
even bigger RAM's available like the ISP1024 from DVS 
(see Ref. 5), starting with 64 Mbyte boards expandable up 
to 16 Gbyte with an internal data rate at the backpanel 
bus of the system of up to 480 Mbyte/sec. Real-Time- 
Video-Discs typically work at a speed of more than 10 
Mbyte/sec. High speed movement of image plates in 
photogrammetric instruments is in the order of 2.5 cm/sec 
corresponding to a transfer rate of 4 Mbyte for digitized 
photograph at 12.5 micron. In normal measurement mode 
the speed is only 2 to 3 mm/sec corresponding to a 
transfer rate of 1.1 Mbyte for a 1024*1024 display. Roaming 
software should allow virtual image addressing as being 
realized in the Vitec50 board, freeing the user to look for 
reloading images. 
3.3 Processor Speed 
The total amount of floating point operations in the CONTEXT 
MAPPER system during one loop including the resampling 
with bi-linear interpolation for sub-pixel measurement of a 
16x16 window around the floating mark is in the order of 
8000 Flops, resulting in a total of 240.000 Flops with 30 
cycles/sec during normal measurement. In addition the 
on-line correlation and other processing functions, especially 
if the resampling window gets larger, demand a very high 
processing power. Standard processors like the 
MC 68000/68881 as they are used in the SUN 3 series 
computer offer a power of 3 Mips or 7 to 10 Mips (1.1 
Mflops) on the SUN 4. Higher performances can only be 
achieved either with special VLSI processors (see Ref. 6) or 
by multiple processor computers, like the SUN TAAC-1 
giving 25 Mips or 12.5 Mflops or the AT&T's Pixel Mac 
hine PXM 900, a multiple instruction multiple data MIMD 
computer with a performance of up to 820 Mflops.