4th Class Computers Computer Memories Primary Memory or Main Memory

Primary Memory or Main Memory

Category : 4th Class

*        Primary Memory or Main Memory  


*            Types of Main Memory:

  • All computers have main or primary memory to store programs and data .while the computer is running.
  • The main memory has 2 subtypes:RAM (Random Access Memory) and ROM (Read-only Memory).


*    RAM (Random Access Memory) and ROM (Read-only Memory).  


RAM (Random Access Memory)  RAM can be compared to a person's short-term memory and the hard disk to the long-term memory. The short-term memory focuses on work at hand, and can keep only a few facts in view at one time. If short-term memory fills up, your brain is sometimes able to refresh it from facts stored in long-term memory. A computer also works this way. If RAM fills up, the processor needs to continually go to the hard disk to overlay old data in RAM with new, slowing down the computer's operation. RAM is the internal memory that can be read. When people talk about computer memory, they are generally referring to the RAM. RAM is volatile i.e. its contents are lost when power is turned off. RAM also has a limited storage capacity. RAM (random access memory) is the place in a computer where the operating system, application programs and data in current use are kept so that they can be quickly reached by the computer's processor. RAM is much faster to read than the other kinds of storage in a computer such as the hard disk, floppy disk and CD-ROM. However, the data in RAM stays there only as long as your computer is running. When you turn the computer off, RAM loses its data. When you turn your computer on again, your operating system and other files are once again loaded into RAM, usually from your hard disk. RAM is a type of computer memory that can be accessed randomly; that is, any byte of memory can be accessed without touching the preceding bytes. RAM is the most common type of memory found in computers and other devices, such as printers. There are two different types of RAM: DRAM (Dynamic Random Access Memory) and SRAM (Static Random Access Memory). The two types differ in the technology they use to hold data. In common usage, the term RAM refers to the main memory or the memory available to the programs. For example, a computer with 8MB RAM has approximately 8 million bytes of memory that programs can use.  


*    ROM (Read-only memory)

In this memory, information once stored remains fixed i.e. it cannot be changed. Severally, ROM contains a set of Start-up instructions, that is, what to do when a computer is turned on. The contents of ROM remain stored even if power is turned off; hence it is also referred to as non-volatile memory. ROM is a class of storage media used In computers and other electronic devices. Since data stored in ROM cannot be modified quickly or easily, it s mainly used to distribute firmware software that is very closely tied to specific hardware and unlikely to require frequent updates). (See Figure 4.2.3) However, more modern types of ROM such as PROM (Programmable Read-Only Memory) and EPROM (Erasable Programmable Read-Only Memory) can be erased and re-programmed multiple times; they are still described as  ROM "(Read-only Memory) because the reprogramming process is generally less frequent, comparatively slow and often does not permit writing to individual memory locations randomly.  



*   PROM (Programmable Read-Only Memory)  

PROM is a memory chip on which data can be written only once. Once a program has been written onto a PROM, it remains there forever. Unlike RAM, PROM retains their contents when the computer is turned off. The difference between a PROM and a ROM is that a PROM is manufactured as blank memory, whereas a ROM is programmed during the manufacturing process. To write data onto a PROM chip, you need a special device called a PROM programmer or PROM burner. The process of programming a PROM is sometimes called burning the PROM. A PROM is a form of digital memory where the setting of each bit is locked by a fuse or antiques. Such PROM is used to store programs permanently. The key difference from a ROM is that the programming is applied after the device is constructed. These types of memories are frequently seen in video game consoles, mobile phones, RFID (Radio-Frequency Identification) tags, implantable medical devices, HDMI (High- Definition Multimedia Interfaces) and in many other consumer and automotive electronics products. (See Figure 4.2.4)  




*      EPROM (Erasable programmable read-only memory)  

An EPROM is a special type of PROM that can be erased by exposing it to ultraviolet light. Once it is erased, it can be reprogrammed. EPROM is a special type of memory that retains its contents until it is exposed to ultraviolet light. The ultraviolet light clears its contents, making it possible to reprogram the memory. To write and erase an EPROM, you need a special device called a PROM programmer or PROM burner. EPROM is a rewritable memory chip that holds its content without power. EPROM chips are written on an external programming device before being placed on the circuit board. The chip requires an expensive ceramic chip package with a small quartz window that is covered with opaque, sticky tape. For reprogramming, the chip is extracted from the circuit board, the tape is removed and it is placed under an intense UV (Ultraviolet) light for approximately 20 minutes. An EPROM differs from a PROM in the sense that a PROM can be written to only once and cannot be erased. EPROM is used widely in personal computers because they enable the manufacturer to change the contents of the PROM before the computer is actually shipped.  This means that bugs can be removed and new versions can be installed shortly before delivery. (See Figure 4.2.5)  







 Given below are the statements about primary memory. Select the correct statements.

1. Primary memory is also known as main memory.

2. ROM and RAM are the two subtypes of primary memory.

3. ROM and hard disk are the short term memory of a computer,

4. The contents of ROM remain stored even if power is turned off.

(A) 1 and 2                                                         

(B) 2 and 3

(C) 1, 2 and 4                                     

(D) All of these

(E) None of these  


Answer: (c)


Correct Option:

(C) Statements 1, 2 and 4 are correct.

Incorrect Options:

(A) Not only statements 1 and 2 are correct but statement 4 is also correct. Therefore, option (A) is incorrect.

(B) Statement 2 is correct but statement 3 is incorrect. Therefore, option (B) is incorrect.

(D) All the given statements are not correct. Therefore, option (D) is incorrect.

(E) All the given statements are not incorrect. Therefore, option (E) is incorrect.    



 Match the following:                

       A                                                         B

1. RAM                                         i.   Rewritable memory chip

2. ROM                                        ii.   Written only once

3.  PROM                                     iii.   Volatile

4.  EPROM                                   iv.  Non-volatile

(A) 1, iii; 2, iv; 3, ii; 4, i

(B) 1, iv; 2, iii; 3, ii; 4, i

(C) 1, i; 2, ii; 3, iii; 4, iv

(D) 1, ii; 2, i; 3, iv; 4, iii

(E) 1, iii; 2, ii; 3, iii; 4, i  


Answer: (A)


Correct Option:

(A) Option (A) is matched correctly.

Incorrect Options:

(B) Option (B) is matched incorrectly.

(C) Option (C) is matched incorrectly.

(D) Option (D) is matched incorrectly.

(E) Option (E) is matched incorrectly.

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