In computer memory, what key characteristic of read only memory ROM makes it especially useful for storing important start up instructions?

Introduction / Context:
This question is about basic computer memory concepts, specifically the role of read only memory, usually abbreviated as ROM. In every computer, certain critical instructions must be available immediately when the machine is powered on. These instructions are often stored in ROM. To understand why ROM is suitable for this purpose, you must know its key characteristic compared to other types of memory such as random access memory RAM.

Given Data / Assumptions:

• The memory type mentioned is read only memory, ROM.
• The question asks which characteristic makes ROM useful.
• Options suggest ideas about non volatility, update capability, storage size, interchangeability and speed.
• We assume a standard definition where ROM is mostly written once and then used many times for reading.

Concept / Approach:
ROM is a type of non volatile memory, which means that the data stored inside it remains even when electrical power is turned off. This is in contrast to RAM, which is volatile and loses its contents when power is removed. Because ROM retains data permanently or semi permanently, it is ideal for storing firmware and start up instructions that the computer needs every time it boots. The fact that ROM is not meant to be updated frequently by the user is actually a limitation, not the feature that is being highlighted as useful in this question.

Step-by-Step Solution:
Step 1: Recall that when a computer is turned on, it must execute a fixed set of instructions to test hardware and start the operating system. Step 2: These instructions are stored in firmware, which is commonly placed in ROM chips on the motherboard. Step 3: The most important requirement for these instructions is that they must still be present even after the power has been off for a long time. Step 4: ROM satisfies this requirement because it is non volatile memory. Non volatile means that data does not disappear when power is removed. Step 5: Option b states this property directly: data in ROM is non volatile and remains stored even without electrical power. Step 6: Option a suggests that ROM information can be easily updated, which is not generally true for basic ROM, and is not the reason it is useful. Step 7: Option c claims ROM provides very large amounts of inexpensive storage, but large cheap storage is more characteristic of devices such as hard disks or flash storage. Step 8: Option d mentions swapping ROM chips between different brands of computers, which is not a standard advantage and often not possible. Step 9: Option e talks about processing speed, but ROM is usually slower than RAM and is not used to speed up all programs. Step 10: Therefore, the correct answer is the non volatile nature of ROM data.

Verification / Alternative check:
When you unplug a computer and then start it the next day, it immediately begins the boot process. The instructions that enable this are stored in firmware chips that do not lose their content when the computer is turned off. This behaviour clearly shows non volatility. RAM modules, on the other hand, lose all data when the computer is powered down. Textbooks and exam guides underline this contrast and specifically state that ROM is used to store start up programs because it is non volatile, confirming option b as the intended answer.

Why Other Options Are Wrong:
Easy updating is not a general property of ROM. Some special types like flash memory can be rewritten, but traditional ROM is programmed once. Large inexpensive storage is more associated with hard drives or other secondary storage devices. Swapping ROM chips between machines is rare and not the main reason ROM is considered useful. Increasing processing speed is related to cache memory and RAM performance, not to ROM, which is usually slower to access.

Common Pitfalls:
Students sometimes confuse ROM with other memory types such as EEPROM or flash memory and think frequent updating is the main advantage. Another common mistake is to focus only on the word read in ROM and assume that read speed or protection from writing is the key point. For exam purposes, the central feature you should remember is that ROM is non volatile, making it ideal for storing important programs that must persist across power cycles.

Final Answer:
The useful characteristic of ROM is that data in ROM is non volatile and remains stored even when there is no electrical power.