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Large Scale Integration; Memories
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There are a number of types of memory which can be used as ICs in digital electronics. These include
a. Random-Access Memory (RAM), wherein each memory word is accessed for reading or writing via a specific address, access time being approximately equal for any combination of successive locations.
b. Serial Access Memory (SAM), wherein the memory consists of a circular shift register (serial output connected to serial input). A counter keeps track of the "address" of the bit available for reading and writing (the serial output and input bits). To read or write a given address, the register is shifted until the counter matches the desired address: clearly a large change of address takes longer than a short one.
c. Read-Only Memory (ROM), in which the binary contents are wired in at the factory as a step in the 1C manufacturing procedure. These act like PAMs, except it is not possible to change the contents. Although it is possible to obtain custom-designed ROMs, they are too expensive for production in small quantities.
d. Programmable ROMs (PROMs), which can be written using special equipment. These hold their contents until erased with high-intensity ultraviolet light and re-programmed.
e. Programmed Logic Arrays (PLAs), some of which can also be programmed, do not have a full-scale memory complement, but are an expensive way of making a ROM-like device, in which not all inputs codes correspond to defined outputs and a given output can be specified by more than one input code.
RAMs are used for temporary data storage because they are volatile: that is their contents are lost if power is removed. ROMs, PROMs, and PLAs are non-volatile, but cannot be written on during normal operation.
A number of new memory types have recently appeared. We can expect corelike RAMs to become available in the near future.
RAMs, being used for temporary data storage, are good "scratch pads" for digital devices; they are used as computer memories for the full range of computer sizes, often in a mixture of ROM, RAM, and core memory.
ROMs and PROMs are used for permanent storage, such as the programs in microcomputers, and start-up programs in larger machines. They are also used to sequence sequential machines from one state to the next, and they are very useful for data conversion, table lookup (trigonometric tables, for example), and generation of complex logical functions. A PROM is used to test a new memory content: if it is correct, a ROM is manufactured with the same content if the number of devices or speed requirements (ROMs are faster) justify the expense; PROMs are used for slower devices produced in smaller quantities.
Учитесь говорить.
6.17. Прочитайте текст. Используйте информацию текста для беседы на тему «Надежность».
What mostly affects system performance is reliability: while increased speed may provide 5%more throughput (производительность) increased reliability significantly affects the system output. System reliability can be quantified by MTBF (mean-time between failures), which is the reciprocal (обратная величина) of the product of the device failure rate and the number of components.
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In semiconductor memories there are two types of failure mechanisms. The first is a hard error in which the device structure fails. The second, a soft error, is a random, non-recurring error caused by alpha particles.
As memories become denser, their storage area becomes smaller. As a result they can become more sensitive to soft errors.
6.18. Обсудите следующие темы:
1. Core memory. 2. Semiconductor memory. 3. Charge-coupled devices. 4. Magnetic bubble devices. 5. Electron beam-addressed memories.
МАТЕРИАЛЫ ДЛЯ САМОСТОЯТЕЛЬНОЙ ВНЕАУДИТОРНОЙ РАБОТЫ
(ПОСЛЕ ВТОРОГО ЗАНЯТИЯ)
Учитесь читать и переводить.
Текст 6.8. Просмотрите текст. Озаглавьте его. Аргументируйте свой выбор заголовка. Прочитайте текст еще раз. Подготовьте сообщение о разных типах памяти.
The electron beam is an addressing pointer of high definition and energy density that can easily be deflected. In storage tubes of the 1940's there were severe limitations to such addressing because of the use of surface charge storage and inadequacies in focusing and deflecting the beam. Two recent innovations, storage within a semiconductor and compounded deflection, may bring us closer to realizing the inherent potential of beam addressing.
The addressing is in two parts. First, the beam is deflected by a short conical structure of low aberration and strikes normally one of the appertures of a matrix of lenslets.
The matrix is made up of two metal plates that have an array of holes (an 18 by 18 array on 1.5-mm centres) and are maintained at different potentials. Second, the beam is deflected by bars running along rows and columns between the holes of the matrix. No matter which lenslet is reached, the reduced beam will be subjected to the second deflection. In this compounded deflection the accuracy and stability at each step need only be a small fraction of what would be required with a single step.
Текст 6.9. Прочитайте текст и сделайте обобщение информации об особенностях кэш-памяти.
Cache Memory
A cache memory is a small, high-speed system memory that fits between the CPU and the main memory. It accesses copies of the most frequently used main-memory data. When the CPU tries to read data from the main memory, the cache memory will respond first if it has a copy of the requested data. If it doesn't, a normal main-memory cycle will occur.
Cache memories are effective because computer programs spend most of their memory cycles accessing a very small part of the memory.
A cache memory cell has three components: an address memory cell, an address comparator and a data memory cell. The data and address memory cells together record one word of cached data and its corresponding address in main memory. The address comparator checks the address cell contents against the address on the memory address bus. If they match, the contents of the data are placed on the data bus.
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An ideal cache memory would have many cache memory cells, each holding a copy of the most frequently used main-memory data. This type of cache memory is called fully associative because access to the data in each memory cell in through the data's associated, stored address.
Not all locations in the memory address space should be cached. Hardware I/O address shouldn't be cached because bits in an I/O register can and must change at any time, and a cache copy of an earlier I/O state may not be valid.
6.19. Изучите таблицу "Memory Technology". Дополните ее известными вам данными о типах памяти.
Memory Technology
| Type | Predominant Technologу | Cycle or access time |
| Registers and discrete bit storage | Monolithic integrated circuits | 50 to 500 nanoseconds |
| High speed control and scratch-pads | Planar thin films | 100 to 500 nanoseconds |
| High speed internal main memories | Magnetic core | 0.3 to 5 microseconds |
| Random-access auxiliary storage | Magnetic core | 2 to 10 microseconds |
| On-line auxiliary storage | Electromechanical disc files | 15 to 150 milliseconds |
| Off-line auxiliary storage | Magnetic tape serial access | Serial |
| … | … | … |
6.20. Подготовьте сообщение для обсуждения тем 'The State-of-art and Future Developments of Memory Technologies".
ИТОГОВЫЕ ЗАНЯТИЯ
I. а) Составьте схему, показывающую основные направления применения микроэлектроники в обществе.
б) Используя вашу схему, подготовьте сообщение "Application Fields of Microelectronics: Material Production, Non-productive Sphere, Personal Uses".
II. Проведите групповую научно-техническую конференцию по проблемам микроэлектроники и перспективам ее развития.
Темы, предлагаемые для обсуждения:
1. In the world of microelectronics.
2. From the history of microelectronics.
3. The top priorities in the field of microelectronics for the next decade.
4. Prospects of the IC's design.
5. Microprocessors: the state-of-art.
6. The mairi problems the designer of a microelectronic device is faced with nowadays.
7. From the history of Computer Science.
8. Fantastic possibilities of computer and information systems.
9. Progress in the computer revolution.
10. Man-machine systems.
11. Automatic control systems.
12. Systems for computer translation.
13. The advent of minicomputers brings a higher level of information culture.
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