Difference Between Serial And Random Access Memory Define
Specifically, why does this Wikipedia article on Direct Access Storage Devices distinguish between the two: whereas this article on random access doesn't: In computer science, random access (sometimes called direct access) is the ability to access an element at an arbitrary position in a sequence in equal time, independent of sequence size. What's the difference between RAM and ROM? Read-only memory, or ROM, is a form of data storage in computers and other electronic devices that can not be easily altered or reprogrammed. RAM is referred to as volatile memory and is lost when the power is turned off whereas ROM in non-volatile and the.
A serial access storage device stores and retrieves data items in a linear, or sequential, order. Magnetic tape is the only widely used form of serial access storage. Random:A random access device, also called a direct access device, isn't restricted to any specific order when accessing data. Sequential access memory. Magnetic sequential access memory is typically used for secondary storage in general-purpose computers due to their higher density at lower cost compared to RAM, as well as resistance to wear and non-volatility. Magnetic tape is the only type of sequential access memory still in use; historically, drum memory has also been used.
The memory of a computer is classified in the two categories primary and secondary memory. Primary memory is the main memory of the computer where the currently processing data resides. The secondary memory of the computer is auxiliary memory where the data that has to be stored for a long time or permanently, is kept. The basic difference between primary and secondary memory is that the primary memory is directly accessible by CPU whereas, the secondary memory is not directly accessible to CPU. Let us discuss some more differences between Primary and secondary memory with the help of the comparison chart shown below.
Content: Primary Vs Secondary Memory
|Basis for Comparison||Primary Memory||Secondary Memory|
|Basic||Primary memory is directly accessible by Processor/CPU.||Secondary memory is not directly accessible by CPU.|
|Altered Name||Main memory.||Auxiliary memory.|
|Data||Instructions or data to be currently executed are copied to main memory.||Data to be permanently stored is kept in secondary memory.|
|Volatility||Primary memory is usually volatile.||Secondary memory is non-volatile.|
|Formation||Primary memories are made of semiconductors.||Secondary memories are made of magnetic and optical material.|
|Access Speed||Accessing data from primary memory is faster.||Accessing data from secondary memory is slower.|
|Access||Primary memory is accessed by the data bus.||Secondary memory is accessed by input-output channels.|
|Size||The computer has a small primary memory.||The computer has a larger secondary memory.|
|Expense||Primary memory is costlier than secondary memory.||Secondary memory is cheaper than primary memory|
|Memory||Primary memory is an internal memory.||Secondary memory is an external memory.|
Definition of Primary Memory
Primary memory is the main memory of computer system. The instructions that have to be currently executed is copied to the primary memory because CPU can directly access the data from primary memory. Accessing data from primary memory is faster as it is an internal memory and processor accesses data from primary memory using data bus.
The primary memory is usually volatile in nature which means data in primary memory does not exist if not saved, in case the power failure occurs. The primary memory is semiconductor memory and is more expensive than secondary memory. The primary memory capacity is limited in computer and is always smaller than secondary memory.
Primary memory can be divided into two types of memory that are RAM (Random Access Memory) and ROM (Read Only Memory).
RAM is a both read and write memory. The data which has to be currently processed is kept in RAM which can be quickly accessed by the CPU. RAM is volatile and loses data if the power is switched off. RAM can be static or dynamic.
ROM is a read only memory; its content can not be altered. It has the instructions that are used when the system is booted up. ROM is a non-volatile memory i.e. it retains its content even if the power is switched off. The types of ROM are PROM, EPROM and EEPROM.
Definition of Secondary Memory
Secondary memory is an auxiliary memory of the computer. The data that has to be permanently stored is kept in secondary memory. The CPU can not directly access the data in secondary memory. The data has to be initially copied to primary memory then only it can be processed by CPU. Hence, accessing data from secondary memory is slower. The secondary memory can be accessed using the input-output channel.The secondary memory is nonvolatile in nature, which means that the content of the secondary memory exist even if the power is switched off. The secondary memory is magnetic memory or optical memory and it available at cheaper rates as compared to the primary memory.
Secondary memory is available in bulk and always larger than primary memory. A computer can even work without secondary memory as it an external memory. The examples of secondary memory are the hard disk, floppy disk, CD, DVD, etc.
Key Differences Between Primary and Secondary Memory
- The key difference between primary and secondary memory is that primary memory can be directly accessed by the CPU whereas, the CPU can not directly access the secondary memory.
- The primary memory of the computer is also known as the main memory of the computer. However, secondary memory is known as auxiliary memory.
- The data that is to be currently processed is in primary memory whereas, the data that has to be permanently stored is kept in secondary memory.
- Primary memory is a volatile memory whereas, the secondary memory is a non-volatile memory.
- Primary memories are semiconductor memories whereas; the secondary memories are the magnetic and optical memories.
- Data accessing speed of the primary memory is faster than secondary memory.
- Primary memory is accessed by the data bus. On the other hand, secondary memory is accessed using input-output channels.
- Primary memory’s capacity is always smaller than secondary memory’s capacity.
- Primary memory is costlier than secondary memory.
- Primary memory is an internal memory whereas, secondary memory is an external memory.
Primary memory is expensive and is available in limited in size in a computer. Secondary memory is cheaper and is present in bulk in the computer. Computer can even work without secondary memory but not with out primary memory.
Your computer probably uses both static RAM and dynamic RAM at the same time, but it uses them for different reasons because of the cost difference between the two types. If you understand how dynamic RAM and static RAM chips work inside, it is easy to see why the cost difference is there, and you can also understand the names.
Function Random Access Memory
Dynamic RAM is the most common type of memory in use today. Inside a dynamic RAM chip, each memory cell holds one bit of information and is made up of two parts: a transistor and a capacitor. These are, of course, extremely small transistors and capacitors so that millions of them can fit on a single memory chip. The capacitor holds the bit of information -- a 0 or a 1 (see How Bits and Bytes Work for information on bits). The transistor acts as a switch that lets the control circuitry on the memory chip read the capacitor or change its state.
A capacitor is like a small bucket that is able to store electrons. To store a 1 in the memory cell, the bucket is filled with electrons. To store a 0, it is emptied. The problem with the capacitor's bucket is that it has a leak. In a matter of a few milliseconds a full bucket becomes empty. Therefore, for dynamic memory to work, either the CPU or the memory controller has to come along and recharge all of the capacitors holding a 1 before they discharge. To do this, the memory controller reads the memory and then writes it right back. This refresh operation happens automatically thousands of times per second.
This refresh operation is where dynamic RAM gets its name. Dynamic RAM has to be dynamically refreshed all of the time or it forgets what it is holding. The downside of all of this refreshing is that it takes time and slows down the memory.
Static RAM uses a completely different technology. In static RAM, a form of flip-flop holds each bit of memory (see How Boolean Gates Work for detail on flip-flops). A flip-flop for a memory cell takes 4 or 6 transistors along with some wiring, but never has to be refreshed. This makes static RAM significantly faster than dynamic RAM. However, because it has more parts, a static memory cell takes a lot more space on a chip than a dynamic memory cell. Therefore you get less memory per chip, and that makes static RAM a lot more expensive.
So static RAM is fast and expensive, and dynamic RAM is less expensive and slower. Therefore static RAM is used to create the CPU's speed-sensitive cache, while dynamic RAM forms the larger system RAM space.
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