Computers and any electronics are complex devices whose operating principles are not always clear to most ordinary people. What is a ROM and why is a device necessary? Most people will not be able to answer this question. Let's try to fix this misunderstanding.
What is a ROM?
What are they and where are they used? Permanent storage devices (ROM) are non-volatile memory. Technologically, they are implemented as a microcircuit. At the same time, we learned what the acronym ROM is for decryption. Devices for storing user input and installed programs are designed. In the permanent storage device you can find documents, melodies, pictures - i.e. everything that should be stored for months or even years. The amount of memory, depending on the device used, can vary from a few kilobytes (on simple devices having one silicon crystal, microcontrollers for example) to terabytes. The larger the volume of the ROM, the more objects can be saved. The volume is directly proportional to the amount of data. If you compact the answer to the question of what ROM is, you should answer: this is
a data warehouse that does not depend on constant voltage.
Hard drives as primary read-only memory devices
The question of what ROM is already answered. Now we should talk about what they are. The main permanent storage device is hard drives. They are in every modern computer. They are used due to their wide possibilities of accumulating information. But at the same time, there are a number of ROMs that use multiplexers
(these are microcontrollers, boot loaders, and other similar electronic mechanisms). With a detailed study, it will be necessary not only to understand the value of ROM. Decoding of other terms is also necessary in order to delve into the topic.
Expanding and complementing ROM capabilities with flash technology
If the user does not have a standard
amount of memory , then you can take advantage of the additional expansion of the capabilities of the ROM provided in the field of data storage. This is done through modern technologies implemented in memory cards and USB-flash drives. They are based on the principle of reusable use. In other words, the data on them can be erased and recorded tens and hundreds of thousands of times.
What is a permanent storage device?
The ROM contains two parts, which are designated as ROM-A (for storing programs) and ROM-E (for issuing programs). Type A read-only memory is a diode-transformer matrix, which is flashed using address wires. This ROM section performs the main function. The filling depends on the material from which the ROMs are made (perforation and magnetic tapes, punch cards, magnetic disks, drums, ferrite tips, dielectrics and their property of the accumulation of electrostatic charges can be used).
Schematic structure of ROM
This electronics object is depicted as a device, which in appearance resembles the connection of a certain number of one-bit cells. The ROM chip, despite the potential complexity and seemingly significant capabilities, is small in size. When storing a certain bit, it is sealed to the case (when zero is recorded) or to the power source (when one is recorded). To increase the capacity of memory cells in read-only memory devices, microcircuits can be connected in parallel. This is what manufacturers do to get a modern product, because a high-performance ROM chip allows them to be competitive in the market.
The amount of memory when used in various units of technology
The amount of memory varies depending on the type and purpose of the ROM. So in simple household appliances such as washing machines or refrigerators, you can have enough installed microcontrollers (with their reserves of several tens of kilobytes), and in rare cases, something more complex is installed. It does not make sense to use a large amount of ROM, because the amount of electronics is small, and the technology does not require complex calculations. For modern TVs, something more advanced is already required. And the pinnacle of complexity is computing technology such as computers and servers, ROMs for which, at a minimum, can accommodate from a few gigabytes (for those released 15 years ago) to tens and hundreds of terabytes of information.
Masked ROM
In cases where recording is carried out using the metallization process and a mask is used, such a permanent storage device is called masked. The addresses of the memory cells are fed to 10 pins, and a specific chip is selected using a special CS signal. Programming of this type of ROM is carried out at the factories; as a result, manufacturing in small and medium volumes is disadvantageous and rather inconvenient. But with large-scale production, they are the cheapest among all permanent storage devices, which ensured their popularity.
They differ schematically from the total mass in that in the storage matrix, the connections of the conductors are replaced by fusible jumpers made of polycrystalline silicon. At the production stage, all jumpers are created, and the computer believes that logical units are written everywhere. But during preparatory programming, an increased voltage is applied, with the help of which logical units are left. When applying low voltages, the jumpers evaporate, and the computer reads that there is a logical zero. By this principle, programmable read-only memory devices operate.
Programmable Read Only Memory
EEPROMs turned out to be convenient enough in the process of technological manufacturing so that they could be resorted to in medium and small-scale production. But such devices also have their limitations - for example, you can record a program only once (due to the fact that jumpers evaporate once and for all). Due to such an inability to use read-only memory repeatedly, it must be thrown away when recording incorrectly. As a result, the cost of all manufactured equipment increases. Due to the imperfection of the production cycle, this problem pretty much occupied the minds of developers of memory devices. The way out of this situation was the development of ROM, which can be re-programmed repeatedly.
UV or electric erase ROM
And they got the name "permanent storage device with ultraviolet or electric erasure." They are created on the basis of a storage matrix in which memory cells have a special structure. So, each cell is a MOS transistor in which the gate is made of polycrystalline silicon. Sounds like the previous option, right? But the peculiarity of these ROMs is that silicon is additionally surrounded by a dielectric with wonderful insulating properties - silicon dioxide. The principle of operation here is based on the content of the induction charge, which can be stored for decades. There are features to erase. So, for an ultraviolet ROM device, it is necessary to hit ultraviolet rays coming from the outside (ultraviolet lamp, etc.). Obviously, from the point of view of simplicity, the operation of read-only memory devices with electric erasure is optimal, since to activate them, you just need to apply voltage. The principle of electrical erasing has been successfully implemented in such ROMs as flash drives, which can be seen by many.
But such a ROM circuit, with the exception of cell construction, is structurally no different from a conventional masked read-only memory. Sometimes such devices are also called reprogrammable. But with all the advantages, there are certain limits to the speed of erasing information: for this action usually takes about 10-30 minutes.
Despite the possibility of rewriting, reprogrammable devices have restrictions on their use. So, electronics with ultraviolet erasure can survive from 10 to 100 dubbing cycles. Then the destructive effect of radiation becomes so noticeable that they cease to function. You can see the use of such elements as storage for BIOS programs, in video and sound cards, for additional ports. But the principle of overwriting is optimal with respect to rewriting. So, the number of overwrites in ordinary devices ranges from 100,000 to 500,000! There are separate ROM devices that can work more, but most users do not need them.