ROMs are storage mediums that are used to store data permanently. So, once it’s been written, there’s no way to rewrite over it. Hence the name, read-only memory.
However, not all ROMs are made for the same purpose. So, if you are curious about the types of ROMs, you are in the right place. there are four primary types of ROMs. Continue reading below to learn more about them.
Types of ROM
Unlike RAM chip, SRAM (Static RAM), or DRAM (Dynamic RAM) memory technology, ROM comes with less variation because of the same implementations of building them. RAM is also referred to as the main memory or primary memory of a computer system. In general, we can differentiate. In terms of computer memory, there are main 4 ROM types. Among the 4 types of ROM in a computer, most of these types are based on semiconductor technology.
Masked ROM is the original ROM type. Among the variations of ROM, MROM is significant. This is not modifiable at all. The information is stored in the chip while manufacturing, and in the whole lifetime, the information can’t be erased or rewritten/modified. These are the oldest types, and so they’re cheap. They are seldom used in modern electrical devices, which makes them rare too. We can still see them in microprocessors or microcontrollers. CD-ROM is very similar to the MROM technology. Masked ROM is also much more compact per bit of info.
In this type, the data is non-modifiable, like the MROM. PROMs (Programmable Read Only Memory) are used to store the firmware of devices that are constant. The main difference or Programmable Read Only Memory from MROM is, while data is stored in MROM during manufacturing, the PROM is manufactured as a blank one. Information is stored in it after manufacturing.
Designers input information into the PROM with a device called “PROM Programmer”. It’s a one-time process. The advantage of PROM is its good for making prototypes and run testing, while still being very cheap.
Erasable-Programmable ROM or EPROM chip is an upgrade over PROMs in which, data can be erased after writing. After programming, EPROM can save its data for up to 35 years or more, which can also be written as many times as needed. To erase it, a specific wavelength of UV light is used for a period of 30-40 minutes.
EPROMs were often seen in previous generation computer BIOS systems. We can erase it for limited amounts of time (1000 times). There are some drawbacks to EPROM with the erasing strategy. Firstly, the erasure isn’t selective, meaning the whole EPROM is erased at once. We can’t erase a portion of EPROM and keep the other portion intact. The second problem is, erasing with UV light for a high volume of memory is much inefficient, and the presence of dust particles inside the erasure window can hamper the process, resulting in some valueless leftovers. For these reasons, EPROMs are losing their value and application fast.
Electrically Erasable Programmable ROM is one of the latest additions in a long line of different ROM chips. These are often seen in modern devices for their efficiency. To erase data, an electrical charge is given to the chip as opposed to the UV lighting. The endurance of data rewriting is much higher (1,000,000 times or more) than before.
Due to the usage of electrical charges, the erasure is selective. We can erase any portion of EEPROM and still keep the other information intact. Although the erasure speed is low, 1 bit each time, still the EEPROM is much more versatile and widely used today. We can take a look at 2 widely used forms of EEPROM:
- EAROM (Electrically Alterable Read-Only Memory)
A special form of EEPROM where at a time 1-bit of information is modified. EAROMs are used to partially rewrite a constant system or to store setup information of a critical system.
- Flash Memory
When the question comes to mind about what are the types of ROM, Flash memory comes to mind. This is a more compact and yet flexible form of EEPROM, where data transfer (read, write, and erase) occurs much faster. This is done by writing data in packages of 512 bytes, as opposed to 1 byte of EEPROMs. Flash memories are widely used as temporary data storage, and although they’re not as reliable as the previous ones, flexibility is much helpful for quick transfers. Flash memories are the fastest type of ROMs with a transfer rate of up to 10GB/s.
Other Forms of ROM
In addition to the main types, for specialized applications, some additional different types of ROM memory are still in use. Such as the previously discussed Optical storage types (CD-RW, CD-R, CD-ROM). In much older computers, Transformer Matrix ROMs were used. In small simple devices like calculators and PCBs, Diode Matrix ROMs can be found. These stores the basic mathematical or numerical functions that don’t change.
Frequently Asked Questions
What are the 3 types of memory in a computer?
The three main types of memory in a computer are, cache memory, ROM and RAM.
What type of memory is ROM?
ROMs are non-volatile memory type, while RAMs are volatile memory.
What are applications of ROM?
ROMs are mostly used to store essential data, like the firmware.
To understand how computers work, it’s essential to understand how non-volatile memories, which is ROM, work. we hope we were able to help you understand it. Thanks for reading.