ROM (Read Only Memory)

(i) ROM:

Read Only Memory is one major type storage media used in computer and other electronic media. Data stored on ROM can not modify easily, so it used to distribute with firmware. Firmware is a software that is very closely tied to specific hardware, and don’t require frequently updating or change e.g. calculator, remote control etc. Data of ROM can not erased nor replace, it written only once by ROM chip’s manufacturer. Hence we can say that ROM is a non volatile memory. (The values stored in ROM are always there, whether the power is on or not). Data on ROM can not change by accidentally or maliciously so it is secure storage area. A simple ROM is uses tiny “fuses” which can blow systematically. A fuse can represent one of two binary states, i.e. on or off. Once a fuse is blown, it can not convert again, so writing of such ROM circuits is one time only. Read-only memory is most commonly used to store system-level programs that we want to have available to the PC at all times. The most common example is the system BIOS program, which is stored in a ROM called the system BIOS ROM. Having this in a permanent ROM means it is available when the power is turned on so that the PC can use it to boot up the system. Remember that when we first turn on the PC the system memory is empty, so there has to be something for the PC to use when it starts up. 

There are basically three types of Rom:

(a) PROM (Programmable read only memory):

PROM was invented in 1956. A Programmable Read Only memory or Field Programmable Read Only (FPROM) is a form of digital memory where the setting of each bit is locked by fuse or anti-fuse. This type of ROM can be programmed using special equipments only once and never overwrite. It is similar to a way a CD-ROM recorder works, it writes a CD once and then it can read many times.

Advantages of PROM:

·         Very reliable to use

·         Permanent store

·         Very less expensive

·         Built by integrated circuits, rather than discrete components.

·         Fast readable, within nanoseconds.

(b) EPROM (Erasable Programmable Read Only Memory):

The EPROM was invented by Dov Frohman in 1971. An EPROM is a ROM that can be erased and reprogrammed. In this type of ROM a little glass window is installed at the top of the ROM package, through which we can actually see the chip that holds the memory. Ultraviolet light of a specific frequency can be shined through this window for a specific period of time, which will erased the EPROM and allow it to be reprogrammed again. The glass window covered with a foil label to prevent accidental erasure by sun light. This technology is same as CD-RW (CD- Rewritable). EPROM comes in different shapes and sizes, depends on manufacturer.

Advantage of EPROM:

·         Permanent store

·         Durability

·         Very Flexibility

·         Reusability (one or two time)

·         Fast Readable

(c) EEPROM (Electrically Erasable Programmable Read Only Memory:

This type of ROM is very useful and having the next level of eras-ability. This ROM erased by a software control. This is very flexible Rom and used for holding BIOS programs. Whenever we talk about the “flash BIOS” or up-gradation of BIOS, then it refers to BIOS EEPROM with a special software program. EEPROM can be programmed and erased electrically using field electron emission. However this feature does not obsolete the feature of read only from this memory, because the EEPROM may be rewrite once in a year or so compared to RAM which can rewrite many times per second. USB flash drive is one of good example of EEPROM.

Advantages of EEPROM:

·         Permanent store

·         More durable from EPROM

·         Reusability (Many times)

·         Fast Readable

·         Can be used in flash drives like pen drive etc.

Statistical Averages

Statistical Averages: -

Human mind can’t understand and differentiate the sophisticated data. Using classification and tabulation a mass of data can be represented in the short and understandable frequency distribution. However, these methods do not represent the all important characteristics of the series of data. According to Ronald A Fisher “The inherent ability of the human mind to grasp, in the entirety, a large body of numerical data, forces us to seek relatively few constants that will adequately describe the data.” To represent the characteristics of a group of data in a summary we need to calculate the measures of central tendency.

Definition of Statistical average as given by different users:

1. According to Croxton and Cowden

“An average is a single value within the range of the data that is used to represent all of the values in the series. Since an average is somewhere within the range of data, it is sometime called a measure of central value.”

2. According to Clark

          “An average is an attempt to find one single figure to describe whole of figure.”

3. According to A.E. Waugh

          “An average is a single value selected from a group of values to represent them in some way – a value which is supported to stand for whole group, of which it is a part, as typical of all the values in the group.”

4. According to Simpson and Kafka

          “A measure of central tendency is a typical value around which other figures congregate.”

5. Kellog and Smith

          “An average is sometime called a ‘measure of central tendency’ because individual values of the variable usually cluster around it.”

On the basis of above definition we can say that “An average is a single value that represents a group of value. Such a value is of great significance because it represents the characteristics of the whole group. This value of average is frequently referred to as a measure of central tendency.