Semiconductor memory

Date: 2015-10-07; view: 379.

III. Read and translate the following text.

UNIT 6. SEMICONDUCTOR MEMORY

I. Practise reading the following words:

semiconductor, essential, electronics, technology, equipment, processor, increase, associated, sophisticated, requirement, emerge, advantage, imply, special, variety, access, initially, range, typically, array, achieve, especially, capacitor, periodically, environment, voltage, particularly, dynamic, synchronous, magnetic, maintain.

II. Before reading the text try to answer these questions:

1. What types of semiconductor memory do you know?

2. Why is semiconductor memory popular?

3. What is the difference between RAM and ROM?

The primary storage (main memory) of your computer consists of semiconductor memory chips. The most common are memory chips with capacities of 4 and 16 megabits. Plug-in memory circuit boards containing 16 or 32 MB or more of memory chips can be added to your PC to increase its memory capacity and improve the performance of your computer.

The main advantages of semiconductor memory are the following: small size, high speed, shock and temperature resistance. The major drawback of semiconductor memory is its volatility, i.e., uninterrupted electric power must be supplied because the content of memory will be lost.

Memory is the essential element of modern electronics. As processors have become more popular both the number of devices controlled by microprocessors and the requirements for semiconductor memory have also increased. Software associated with the processors and computers has become more sophisticated. With the rapid growth of the requirements for semiconductor memory, a number of technologies and types of memory (ROM, RAM, EPROM, EEPROM, Flash memory, DRAM, SRAM, SDRAM) have appeared. Each type of memory has its own advantages and areas where it can be applied. According to the way electronic semiconductor memory operates, it can be divided into two main categories: RAM and ROM.

RAM stands for «random access memory» and is the working area of the computer, that is, the basic location where the microprocessor stores the required information. It is called ‘random access' because the processor can find information in any cell or memory address with equal speed, instead of looking for the data in the sequential order.

All the information stored in the RAM is temporary, so it is lost when the machine is turned off. Therefore, if we want to use this information later on, we have to save it and store it on a disk. When running an application, the microprocessor finds its location in the storage device (the floppy or hard disk) and transfers a temporary copy of the application to the RAM area. Consequently, the size of RAM is very important if you want to increase the performance of a computer when several applications are open at the same time or when a document is very complex.

The RAM capacity can sometimes be expanded by adding extra chips. These are usually contained in single in-line memory modules or SIMMs, which are installed in the motherboard of the computer.

We can designate a certain amount of RAM space as acache in order to store information that an application uses repeatedly. A RAM cache may speed up our work, but it means that we need enough internal memory or a special cache card.

ROM is an acronym for ‘read only memory', which implies that the processor can read and use information stored in the ROM chip, but cannot put information into it. ROM chips have «constant» information, including instructions and routines for the basic operations of the CPU. These instructions are used to start up the computer, to read the information from the keyboard, to send characters to the screen, etc. They cannot be changed and are not erased when the power is turned off. For this reason, the ROM section is also referred to as firmware.

The most commonly used types of semiconductor memory are listed below.

PROM (Programmable Read Only Memory) can store data written once and this data is known as permanent. Typically PROM consists of useable links array to provide the required data patterns.

EPROM (Erasable Programmable Read Only Memory) can be programmed and erased later.

EEPROM is an Electrically Erasable Programmable Read Only Memory. This is a type of memory where data can be written and erased by using electrical voltage. Like other types of PROM, EEPROM retains the contents of the memory when the power is turned off but it is not so fast as RAM.

Flash memory may be considered as the development of EEPROM technology. Data can be written and erased only in blocks, but it can be read cell by cell individually. In this type of memory programming voltages are used to erase and re-program areas of the chip. Flash memory is non-volatile that makes it particularly useful. As a result, flash memory is widely used in many applications including memory cards for digital cameras, mobile phones, computer memory sticks and many other applications.

Dynamic RAM is a form of random access memory that is often used in personal computers and workstations. DRAM uses a capacitor to store each bit of data, and the level of charge on each capacitor determines whether the bit is logical 1 or 0. However, the information stored on these capacitors is required to be updated periodically.

Static Random Access Memory is a form of semiconductor memory that supports faster read/write time than DRAM (typically 10 ns instead of 60 ns for DRAM). Typically, it is used for caching, while DRAM is used as the main semiconductor memory technology.

Synchronous DRAM is a form of semiconductor memory that runs at higher speed than conventional DRAM.

Magnetic RAM is a non-volatile RAM memory technology that uses magnetic charges to store data and retains it when the power is turned off. Its main advantage is lower power consumption.

IV. Answer the following questions:

1. What is memory used for?

2. What types of memory are mentioned in the text?

3. What is the role of RAM?

4. What is PROM famous for?

5. What type of memory uses a capacitor to store data?

6. What type of memory uses magnetic charges to store data?

7. What is the typical read/write time of DRAM?