Computer Memory

Contents:

• Introduction
• Units of Memory
• Types of Memory
  • cache Memory
  • Primary Memory
  • Secondary Memory
• Data Capture, Storage and Retrival
  • Data Capture
  • Data Storage
  • Data Retrival
• Data Deletion and Recovery

Introduction:

Memory basically means storage media i.e. the hardware on which data is stored. A computer system needs memory to store the data and instruction for processing.

Units Of Memory:

Inorder to measure the amount of data, units of memory are used. A computer system uses binary numbers to store and process data. The binary digits 0 and 1, which are the basic units of memory, are called bits.A bit is smallest unit of memory which can store either a 1 or 0 but not both. Below are the data units

• 1 bit : stores 1/0
• 1 nibble: stores 4 bits
• 1 Byte : stores 8 bits
• 1 KB(Kilobyte) : 1024 Bytes
• 1 MB(Megabyte) : 1024 KB
• 1 GB(Gigabyte) : 1024 MB
• 1 TB(Terabyte) : 1024 GB
• 1 PB(Petabyte) : 1024 TB
• 1 EB(Exabyte) : 1024 PB
• 1 ZB(Zettabyte) : 1024 EB
• 1 TB(Yottabyte) : 1024 ZB

NOTE: In 2020 the total amount of digital data is about 40 ZB

Types of memory:

On the basis of distance from the CPU and speed of the memory device, memory can be classified into 3 types (1) cache memory (2) primary memory (3) secondary memory

cache memory:

cache memory is usually small memory present on the CPU die. cache is very fast as compared to RAM but of very samll size, typically of 1-3mb. only a part of data/program is loaded into the cache for faster access by the microprocessor.

Primary memory:

primary memory means the RAM/ROM which is placed after cache memory is not present on the CPU but on the motherboard. Program and data are loaded into the primary memory before processing. The CPU interacts directly with the primary memory to perform read or write operation. It is of two types viz. (i) Random Access Memory (RAM) and (ii) Read Only Memory (ROM).

RAM is volatile, i.e., as long as the power is supplied to the computer, it retains the data in it. But as soon as the power supply is turned off, all the contents of RAM are wiped out. It is used to store data temporarily while the computer is working. Whenever the computer is started or a software application is launched, the required program and data are loaded into RAM for processing. RAM is usually referred to as main memory

ROM is non-volatile, which means its contents are not lost even when the power is turned off. It is used as a small but faster permanent storage for the contents which are rarely changed. For example, the startup program (boot loader) that loads the operating system into primary memory, is stored in ROM.

Secondary memory:

Primary memory has limited storage capacity and is either volatile (RAM) or read-only (ROM). Thus, a computer system needs auxiliary or secondary memory to permanently store the data or instructions for future use. The secondary memory is non-volatile and has larger storage capacity than primary memory. It is slower and cheaper than the main memory. But, it cannot be accessed directly by the CPU. Contents of secondary storage need to be first brought into the main memory for the CPU to access. Examples of secondary memory devices include Hard Disk Drive (HDD), CD/DVD, Memory Card, etc.

Data Capture, Storage and Retrieval:

Computers are good at data processing, inorder to do this the data is to be obtained/captured from external sources, stored into some file or database and when the data is to be processed, then it has to be retrived from the file or database

(A) Data Capturing:

It involves the process of gathering data from different sources in digital form. Some of the possible ways are:

• using barcode scanner get the information about the product
• using keyboard
• using camera sensor to get an image

(B) Data Storage:

After the data is captured through devices/sensors, they are stored on storage medium like HDD, DVD, prndrive etc. the data stored are some sort of representation of binary i.e. 0/1

(c) Data Retrieval:

It involves fetching data from the storage devices, for its processing as per the user requirement.Minimising data access time is crucial for faster data processing.

Data Deletion and Recovery:

deletion of data means that data becomes inaccesible to the user.Deleting digitally stored data means changing the details of data at bit level, which can be very timeconsuming. Therefore, when any data is simply deleted, its address entry is marked as free, and that much space is shown as empty to the user, without actually deleting the data.

Recovery of the data is possible only if the contents/memory space marked as deleted have not been overwritten by some other data. Data recovery is a process of retrieving deleted, corrupted and lost data from secondary storage devices.

There are two security concerns associated with data

• One is its deletion by some unauthorised person or software. These concerns can be avoided by limiting access to the computer system and using passwords for user accounts and files, wherever possible. There is also an option of encrypting files to protect them from unwanted modification.
• The other concern is related to unwanted recovery of data by unauthorised user/software. This concern can be mitigated by using proper tools to delete or shred data before disposing off any old or faulty storage device. Example of software to permanently delete data (1) WipeFile, (2) HardWipe etc

Refernces:

1. NCERT for Class 11

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