In the context of computers and electronics, "mrom" likely refers to MROM, which stands for Mask ROM. It is a specific type of Read-only memory.
Understanding ROM
As per the reference, ROM stands for Read-only memory. This type of computer memory is non-volatile, meaning the data stored in it persists even when the power is turned off. The primary characteristic of ROM is that data can typically only be read from it; it is difficult or impossible to modify the data once it has been programmed.
What is MROM (Mask ROM)?
MROM, or Mask Read-only memory, is the original type of solid-state ROM. The term "mrom" you used is likely a lowercase spelling or a typo for MROM.
Unlike other types of ROM that can be programmed after manufacturing, the data in MROM is permanently programmed into the semiconductor chip during the manufacturing process itself. This is done using a photographic mask (hence the name "Mask ROM").
Key Characteristics of MROM
- Programmed during manufacturing: The data pattern is defined by the physical layout of the circuits on the chip, determined by the mask used in fabrication.
- Non-volatile: Data is retained without power.
- Low Cost (in high volume): Once the initial mask is created, producing large quantities of identical MROM chips is very cost-effective.
- High Density: MROM can store a lot of data in a small space.
- Cannot be modified: The data stored in MROM is fixed and cannot be changed or erased after manufacturing.
How MROM Works
During the wafer fabrication process, the interconnection pattern that defines the stored data is etched onto the silicon chip using a mask. This mask determines whether a connection exists at specific points, representing binary 1s or 0s. Because this is a physical process integrated into the chip's creation, the data is permanent and cannot be altered by the user.
Applications of MROM
Due to its fixed nature and low cost in bulk, MROM was historically used for:
- Storing the boot program (BIOS) in early computers.
- Holding firmware in embedded systems, such as:
- Calculators
- Early video game cartridges
- Simple electronic toys
- Microcontrollers for appliances
- Storing look-up tables or character sets.
MROM vs. Other ROM Types
While MROM is permanent, other types of ROM were developed to offer more flexibility:
| Feature | MROM (Mask ROM) | PROM (Programmable ROM) | EPROM (Erasable PROM) | EEPROM (Electrically Erasable PROM) | Flash Memory (Type of EEPROM) |
|---|---|---|---|---|---|
| Programming | During Manufacturing | Once by user | Multiple times (UV light erase) | Multiple times (Electrical erase) | Multiple times (Block erase) |
| Erasability | None | None | Bulk (UV light) | Byte-by-byte or block (Electrical) | Block (Electrical) |
| Flexibility | Least flexible | Low | Medium | High | High |
| Cost (Small Qty) | High (mask setup cost) | Medium | Medium | High | Medium |
| Cost (Large Qty) | Low | Medium | Medium | Medium | Low |
| Primary Use | High-volume fixed code | Prototypes, low-volume fixed code | Development, infrequent updates | Frequent updates, configuration data | Storage (USB drives, SSDs, etc.), firmware |
The Evolution Away from MROM
While cost-effective for mass production of completely static code, MROM's inability to be updated became a significant drawback as technology advanced. The need for flexibility, bug fixes, and feature updates led to the development and widespread adoption of programmable and erasable ROM technologies like PROM, EPROM, EEPROM, and especially Flash memory, which is dominant today for storing firmware and data that needs to be updated.
In summary, "mrom" most likely refers to MROM, the original form of Read-only memory where the contents are permanently set during manufacturing.
