Random access memory devices, time

Today, dynamic random-access memories (DRAMs) are transistor/capacitor-based semiconductor devices, with access times measured in nanoseconds and very low costs. Core memories were made of magnetic rings not less than a millimetre in diameter, so that a megabyte of memory would have occupied square metres, while a corresponding DRAM would occupy a few square millimetres. Another version of a DRAM is the read-only memory (ROM), essential for the operation of any computer, and unalterable from the day it is manufactured. We see that developments in magnetic memories involved dramatic reductions in cost and... 

For non-volatile random access memories (NV-RAMs in which the stored information is retained even if power to the chip is interrupted), ferroelectrics serve not just as capacitors (as in the case of the DRAM, described below), but as the memory element itself. Their principal advantages in this application are low-voltage (1.0 V) operation, small size (about 20% of a conventional EEPROM cell - and cost is proportional to size once high-yield production is achieved), radiation hardness (not just for military applications but also for satellite communications systems) and very high speed (60 ns access time in commercial devices, sub-nanosecond in laboratory tests on single cells). 

This increase in circuit density is made possible only by decreasing the minimum feature size on the chip. Figure 2 illustrates the decrease in minimum feature size as a function of time for dynamic random access memory (DRAM) devices. In 1975, the 4-kilobit DRAM (4 X 10 memory cells or about 8.2 X 10 transistors) had features in the 7-9-(xm range, and by 1987,... 

Figure 1.20. Microlithographic trends in minimum device feature size and imaging technology. The figure illustrates the time evolution of random access memory (RAM) devices.

Deep levels influence a variety of device parameters. For example, in minority carrier devices they influence the recombination and generation lifetimes. The lifetime in turn controls junction currents and refresh times in dynamic random access memories. For this reason we discuss lifetimes. Defects... 

The autosampler functions as a separate IEEE-488 device, distinct from the source system. It also Incorporates its own internal microcomputer and associated memory. It allows random access of any sample In the tray at any time during the analysis. Using the autosampler for sample introduction allows the analyst to perform other analysis-related tasks while an analysis is taking piace. Including the system controller, both monochromators, the RF system and the autosampler, the instrument assembly contains five separate microprocessors. 

ROM is a form of storage media used in computers and other electronic devices. Because data stored in ROM cannot be modified, it is mainly used as firmware (software that is very closely tied to specific hardware and unlikely to require frequent updates). In its strictest sense, ROM refers only to mask ROM (the oldest type of solid state ROM), which is fabricated with the desired data permanently stored in it, and thus can never be modified. However, more modern types such as EPROM and flash EEPROM can be erased and reprogrammed multiple times they are stUl described as read-only because the reprogramming process is generally infrequent, comparatively slow, and often does not permit random access writes to individual memory locations. 

RAM is a form of computer data storage. RAM takes the form of ICs that allow stored data to be accessed in any order (i.e., at random). The word random thus refers to the fact that any piece of data can be returned in a constant time, regardless of its physical location and whether or not it is related to the previous piece of data. RAM is a volatile type of memory, where the information is lost after the power is switched off. By contrast, storage devices such as magnetic discs and optical discs rely on the physical movement of the recording medium or a reading head. In these devices, the movement takes longer than data transfer, and the retrieval time varies based on the physical location of the next item. 

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