Lecture
Это окончание невероятной информации про запоминающие устройства .
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semiconductor (integral) and other ROMs are distinguished.
Currently, the most common type are semiconductor integrated ROMs.
Semiconductor integrated ROMs have all the same advantages as semiconductor memory devices with arbitrary inversion. Moreover, unlike the latter, they are non-volatile. Permanent memories have a large capacity on a single chip (in the single package of an integrated circuit). The positive feature of integrated ROMs is that some types of these devices allow the consumer to program them (input information) under operating conditions and even multiple reprogramming.
By the type of GE that establishes or breaks the connection (contact) between horizontal and vertical lines, there are bipolar and MOS-ROM circuits. Bipolar ROMs have a sampling time of 3-5 ns. Permanent memory on MOS circuits have a large capacity in a single crystal (case), but also less speed: the sampling time is 10-15 ns.
According to the most important feature - the method of entering information (programming), there are three types of integrated semiconductor ROMs:
· Programming in the manufacturing process by applying with the help of photo masks at the points of contact jumpers needed by the consumer.
· Programming by burning jumpers or breakdown of pn junctions to destroy or form connections between horizontal and vertical lines (one-time programming) that the user can carry out using a special programmer.
· Electric reprogramming, in which information is recorded in a ZM electrically, and erasing the information necessary to change the contents of the ROM is performed by exposing the ZM to ultraviolet radiation or electrically (multiple programming). Programming time for both types of EPROM is approximately the same and is about 30-100 s per 1 megabit of memory.
Programmable photomasks and burning ROM can be built on the basis of both bipolar and MOS-circuits. Reprogrammable ROMs use only MOS-circuit capable of storing charges.
Flash memory by the type of storage elements and the basic principles of operation is similar to EEPROM type memory (PROM) with electrical reprogramming. However, a number of architectural and structural features make it possible to distinguish it into a separate class. The development of flash memory is considered the culmination of the development of memory circuitry with electrical erasure of information, and became possible only after the creation of ultrathin film technology. The time of electrical reprogramming of flash memory, in contrast to existing PROMs, is very short and amounts to hundreds of nanoseconds. This allows them to be used as operational external storage devices such as hard disk. However, the number of flash rewrite cycles is limited.
In flash memory schemes, individual words cannot be erased; information is erased either for the entire memory at the same time, or for sufficiently large blocks. This allows you to simplify the scheme of memory, ie, contributes to the achievement of a high level of integration and performance at a lower cost. Technologically, flash memory circuits are executed with high quality and have very good parameters.
The term flash, according to one of the versions, is associated with a characteristic feature of this type of memory — the possibility of simultaneously erasing its entire volume. According to this version, before the advent of flash memory, devices that were used to automatically erase the stored information when attempting to gain unauthorized access were called flash devices (flash, instant) when storing secret data. This name was transferred to memory, which possessed the property of quickly erasing the entire data array with a single signal.
Simultaneous erasing of all memory information is implemented most simply, but it has the disadvantage that even replacing one word in memory requires erasing and a new record for the entire memory as a whole. For many applications, this is inconvenient; therefore, along with the circuits with the simultaneous erasure of the entire contents, there are circuits with a block structure in which the entire memory array is divided into blocks that can be erased independently of each other. The size of such blocks varies greatly: from 256 bytes to 128 KB.
The number of reprogramming cycles for flash memory, although large, is limited, i.e. overwrite cells are "worn out". In order to increase the longevity of the memory, special algorithms are used in its work, which contribute to the “leveling” of the number of rewrites in all the blocks of the chip.
Соответственно областям применения флэш-память имеет архитектурные и схемотехнические разновидности. Двумя основными направлениями эффективного использования флэш-памяти являются хранение не очень часто изменяемых данных (обновляемых программ, в частности) и замена памяти на магнитных дисках.
Для первого направления, в связи с редким обновлением содержимого, параметры циклов стирания и записи не столь существенны, как информационная емкость и скорость считывания информации. Стирание в этих схемах может быть как одновременным для всей памяти, так и блочным. Среди устройств с блочным стиранием выделяют схемы со специализированными блоками – несимметричные блочные структуры – по имени так называемых boot-блоков, в которых информация надежно защищена аппаратными средствами от случайного стирания. Эти ЗУ называют boot block flash memory. Boot-блоки хранят программы инициализации системы, позволяющие ввести ее в рабочее состояние после включения питания.
Микросхемы для замены жестких магнитных дисков (flash-file memory) содержат более развитые средства перезаписи информации и имеют идентичные блоки (симметричные блочные структуры). Накопители подобного типа широко используются фирмой Intel. Имеются мнения о конкурентоспособности этих накопителей в применениях, связанных с заменой жестких магнитных дисков для ЭВМ различных типов.
В заключение следует отметить, что в настоящем разделе рассмотрены только основные типы ЗУ и ЗЭ, которые далеко не исчерпывают все разнообразие современной элементной базы устройств памяти ЭВМ.
1. Приведите важнейшие характеристики запоминающих устройств.
2. Классификация ЗУ по принципу действия.
3. Классификация ЗУ по способу реализации в памяти операций обращения.
4. Классификация ЗУ по способу организации доступа.
5. Иерархические уровни памяти современных ЭВМ.
6. Способы организации памяти.
7. Обобщённая структура адресного ЗУ.
8. Обобщённая структура ассоциативного ЗУ.
9. Обобщенная структура аппаратных стеков LIFO и FIFO.
10. Опишите процедуру записи слова в программный стек LIFO.
11. Структура ЗУ типа 2D.
12. Структура ЗУ типа 3D.
13. Структура ЗУ типа 2D-М и её отличие от структур типа 2D и 3D.
14. Классификация ПЗУ по способу программирования.
15. Основные особенности флэш-памяти.
Часть 1 Theme 11. Storage devices Lecture 14
Часть 2 14.5. Flash memory - Theme 11. Storage devices Lecture 14
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Computer circuitry and computer architecture
Terms: Computer circuitry and computer architecture