Memory swapping

The setup shown in Fig. 5.49 can, in principle, be used to record fast changes in the brain at 4 laser wavelengths and 32 detector positions. However, the limited speed of the fibre switch normally allows one to record sequences only for one or two source positions at a time. The result is a total number of 128 to 256 waveforms each 50 to 100 ms or 32 to 64 per TCSPC module. The corresponding readout rate in the memory swapping mode is well within the range of currently used TCSPC modules. However, improved fibre switches may allow one to multiplex a larger number of source positions at a rate of 100 s" or faster. The data transfer rate then exceeds 10 Mbyte/s, and precautions have to be taken to sustain this rate over a longer time. 

Fig. 5.53 20 steps of a TOF sequence recorded at an adult human head by TCSPC memory swapping. Acquisition time 100 ms per curve, ADC resolution 1,024 channels. Diode laser 785 nm, 2.5 mW, detector H5773-20. Left Source-detector distance 8 cm, count rate 1.8T0 s. Right Source-detector distance 5 cm, count rate 4.5T0 s ... 

Fig. 5.125 Bursts of single molecules. Part of a longer sequence recorded by sequencer-controlled memory swapping. 1 ms per step of the sequence, 64 ADC channels...

The purpose of a tabu restriction is to prevent a move from being reversed during the length of the short-term memory, which is a number of future moves specified by the variable tabu size. If, at a given iteration, jobs p(i) and p(j) are swapped, then any move that places job p(i) earlier in the sequence than position i is tabu, until tabu size iterations have occurred or the aspiration level is exceeded. To keep track of which moves are tabu and to free those moves from their tabu status, Laguna et al. define the following data structures... 

Any machine with virtual memory suffers performance degradation when page swaps are too frequent. Some pipelined machines like the TI-ASC (3) or the CDC Star-100 (4) have rather long setup times for their arithmetic pipes. Multiprocessor machines like the Illiac IV (5) are next to useless if the programmer pays no attention to the architecture. These features all directly impact the user they have not been effectively hidden by software at any level. Improvement of this situation could result if compilers took on the burden of optimizing code so as to promote efficient hardware utilization. 

A special memory management unit (MMU), located at FF00, is used to control the 128 s complicated memory map. The MMU interprets memory addresses even before the microprocessor sees them. It permits the programmer to swap between 64K banks of memory, but can leave a small portion of memory as common memory. For example, you don t always want zero page and the stack to disappear when you change banks. The MMU permits you to bank between four 64K banks, and allows multiple banks of 256K, up to one megabyte of memory. 

East Page Mode (PPM) DRAM chips, at the time of the 486/Pentium transition, was the most common type of DRAM. Although its technical designation is PPM DRAM, because it was the most common type of DRAM, everyone just started calling it DRAM. It allowed data to be paged (swapped) into memory faster than earlier versions, thus providing better performance. 

Here s an example of how this might work Say the processor has a large graphic to draw on the screen. It makes a call to the video card and says, Hey, I ve got some video for you, then starts writing to the video area in reserved memory. When this area is full, the video card swaps those full blocks for empty ones from the memory on the card. The video card takes the instructions from the full blocks and uses them to draw the picture on the screen. Table 3.3 shows the most commonly used memory addresses for video cards. 

The virtual memory settings (see Figure 14.14) tell you how much hard drive space is allocated to the system as a swap file. For a review of what virtual memory is, return to Part II, Chapter 13, Windows 95/98. Windows 2000 recommends a particular virtual memory level, but you can add to or subtract from this as you need. Often, certain applications (SQL Server for instance) will need to have Windows 2000 Professional s virtual memory limit raised in order to work properly. Graphics and CAD applications also require raising the virtual memory level, but if this is the case, the setup instructions for the application will generally tell you what modifications need to be made. 

B. The virtual memory settings tell the user how much hard drive space is allocated to the system as a swap file. With minimum RAM on the system illustrated in this question, this setting may need to be modified. 

Fig. 3.9 Unlimited sequential recording by memory bank swapping. When one memory bank is full, the sequencer swaps the banks. While the sequencer writes into one bank, the other one is read by the computer...

InputR = 0 and Inputs = 1 produce one held memory state, whereas swapping the inputs around (InputR = 1 and Inputs = 0) produces the other memory state. It is notable that the condition InputR = 0 aud Inputs = 0 simply holds the previous memory state. The fourth condition (InputR = 1 and Inputs = 1) is usually avoided by adding a small logic array before the device to act as a guard. 

Under RTE II, application programs are either resident on the disc and are swapped into memory only when needed for a task or are, in selected instances, always memory resident for instant accessibility. Disc resident programs are placed into memory to perform a task, but are subject to being swapped back to disc to make way for a higher priority task. 

There is a copy of DAR resident in memory for each GC-MS system. This is to assure quick response during the data acquisition phase. The remaining analysis and control programs are disc resident and are swapped in and out of memory, as needed, on a priority basis. Time spent in DAR is dead time for data collection. When... 

A typical computer system might have three of four different storage media. For example, a personal computer system might have solid state memory, a floppy disc drive, a hard disc drive and a tape back-up unit. Solid state memory provides the high speeds for computations, the floppy disc is useful for swapping data and software, the hard disc provides fast, bulk storage, and the tape back-up unit is required because the hard disc is sealed in its box and its data is vulnerable to malfunction or operator error. It will be noted from Table 9.1 that optical storage systems seem to combine the best properties of floppy disc, hard disc and... 

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