A Read Only Memory (ROM) is a type of computer memory that is non-volatile. As the name suggests data is written once and read many times on these memories. It is classified as computer primary memory alongside RAM.
They are used to store firmware software for devices such as computers, routers, and gaming devices, among other electronic devices. Data in the ROM is permanently stored. However, some types of ROM allows user to update the content or even delete it completely.
The primary function of ROM memory is to store device firmware data. An example of ROM is a BIOS for the computer which is used to store information used when a computer is booting.
Types of ROM memory
Masked Read-Only Memory (MROM)
These are the oldest types of ROM and they store data permanently without the option of making any changes. They are made of integrated circuits. The content of the MROM is coded by the manufacturer and the user cannot change anything on it. In case the MROM data has a problem the device has to be recalled by the manufacturer to replace the memory completely.
MROM memory is cheaper than all the other types of memory. It is also compact in size. These memories are obsolete and hence not common in today’s devices.
Programmable Read-Only Memory (PROM)
Unlike the MROM, PROM memory comes as blank memory that users can program with their data their own way. To program the data to the memory, the user will require a PROM burner or programmer.
The PROM burner is used to program the memory only once with user-specified data. Due to this, it is also called a one-time programmable or user-programmable device
Erasable Programmable Read-Only Memory (EPROM)
EPROMs are ROM memories that can be reprogrammed more than once. They are reprogrammed by exposing them to ultraviolet light. When they are exposed to ultraviolet light for a period of time the data is erased.
You will require a PROM burner to rewrite the data to the memory. Since they can be erased by the use of ultraviolet light they should not be exposed to direct sunlight which has this light. They have a limited number of times that they can be reprogrammed.
Electrically Erasable Programmable Read-Only Memory (EEPROM)
These ROM memories can be modified electrically and don’t require the use of ultraviolet light. They can be reprogrammed many thousands of times without compromising memory.
It has high data access speed than the other types of ROM. data is written or erased byte by byte rather than block. This makes it slower than the flash memory.
These are advanced types of EEPROM memories that can be written or erased block by block rather than byte by byte. They can be reprogrammed as many times as the user may require.
Flash memory has a very high access speed compared to all the other ROM memory available in the market. They are mainly used as removable storage devices to transfer data from one computer to another.
Characteristics of ROM
For a memory to be termed ROM memory it should have the following features.
- Non-volatile. The memory retains the data even when the power goes off. They don’t depend on electrical power ability to maintain data within their circuits.
- Don’t require a refresh. ROM circuitry is in such a way that it doesn’t require to keep refreshing to maintain data, unlike the RAM memory.
- Low power consumption. Reading or writing data requires a minimal amount of power. Again since they don’t need to be refreshed every time it means they don’t consume much power.
- Permanent storage. ROM memories store data permanently or until the user decides to delete it.
Advantages of ROM
- They are cheaper to manufacture and maintain than RAM memory.
- ROMs are non-volatile in nature means data is stored permanently. This means data cannot be lost.
- Since the manufacturer permanently stores data, it is known and can be verified if it is correct.
- They are more reliable to store data even when the power goes off compared to RAM memories.
Disadvantages of ROM memory
- Read-only.ROM memories are mostly read-only which means users don’t have control over making changes to the content.
- Limited storage capacity. These memories have a small storage capacity compared to other storage devices such as hard disks.
- Low access speed than RAM.ROM has a slow access speed when compared to the other primary memory RAM.
- Depending on the type of ROM in use it may require special equipment called PROM burner to write data to the memory.