Which type of computer memory is essentially empty (unprogrammed) when it is manufactured and can be programmed only once by the user?

Introduction / Context:
Different types of read only memory (ROM) are used in computer systems for storing firmware and other data that should not change frequently. These include ROM, PROM, EPROM, and EEPROM. One particular type of memory is shipped from the manufacturer in an essentially empty state and can be programmed once by the user or system designer. This question asks you to identify that memory type.

Given Data / Assumptions:

• The focus is on non-volatile memory types in the ROM family.
• We are interested in the variant that is empty when manufactured and programmed only once.
• EPROM can be erased and reprogrammed using ultraviolet light.
• Standard ROM is factory programmed and not empty when delivered.
• EROM is not a widely recognised standard type in basic textbooks.

Concept / Approach:
PROM stands for Programmable Read Only Memory. When PROM chips are manufactured, all bits are initially set to a default state (often 1) and can be changed once by the customer using a special programming device that permanently burns fuses to store data. After this programming, the contents cannot be changed. This means PROM is essentially empty or blank in a logical sense when produced. EPROM (Erasable PROM) differs because it can be erased with ultraviolet light and reprogrammed multiple times. Factory programmed ROM is not empty; it contains fixed data at manufacture. Thus, the correct answer is PROM.

Step-by-Step Solution:
Step 1: List the main ROM variants: ROM, PROM, EPROM, and EEPROM. Step 2: Recall that PROM is sold to customers who program it once using a programmer device. Step 3: Recognise that before programming, PROM does not contain specific firmware; it is effectively blank. Step 4: Understand that EPROM can be erased and rewritten, so it is not limited to one time programming. Step 5: Note that standard ROM is programmed during manufacturing and is not provided as an empty chip to users. Step 6: Conclude that PROM matches the description of memory that is empty when manufactured and programmable exactly once.

Verification / Alternative check:
Electronics and computer architecture textbooks describe PROM as one time programmable memory. They explain that manufacturers or system designers program PROM chips after hardware design is finalised. The promotional material for PROM devices also emphasises that they ship blank and can be permanently programmed by the customer. EPROM and EEPROM datasheets highlight their erasable and reprogrammable nature, clearly distinguishing them from PROM. This confirms PROM as the correct answer.

Why Other Options Are Wrong:
EPROM (Erasable Programmable Read Only Memory): Can be erased and reprogrammed multiple times using ultraviolet light, so it is not limited to one time programming. EROM (a non-standard or incorrect term): Not a standard memory type in basic computer fundamentals; often appears only as a distractor. ROM (Read Only Memory pre-programmed at the factory): Contains fixed data from the manufacturer and is not blank when delivered to users.

Common Pitfalls:
A frequent confusion is between PROM and EPROM because both contain the words Programmable Read Only Memory. To avoid this, remember that PROM is one time programmable, while EPROM is erasable and reprogrammable. Another pitfall is assuming that all ROM chips arrive with firmware already stored; PROM is the exception where the user performs the initial programming.

Final Answer:
The memory type that is essentially empty when manufactured and programmable only once is PROM (Programmable Read Only Memory).