A memory is just like a human brain. It is used to store data and
instructions. Computer memory is the storage space in computer where
data is to be processed and instructions required for processing are
stored. The memory is divided into large number of small parts called
cells. Each location or cell has a unique address which varies from zero
to memory size minus one. For example if computer has 64k words, then
this memory unit has 64 * 1024=65536 memory locations. The address of
these locations varies from 0 to 65535.
Memory is primarily of three types
- Cache Memory
- Primary Memory/Main Memory
- Secondary Memory
Cache Memory
Cache memory is a very high speed semiconductor memory which can
speed up CPU. It acts as a buffer between the CPU and main memory. It is
used to hold those parts of data and program which are most frequently
used by CPU. The parts of data and programs are transferred from disk to
cache memory by operating system, from where CPU can access them.
Advantages
The advantages of cache memory are as follows:
- Cache memory is faster than main memory.
- It consumes less access time as compared to main memory.
- It stores the program that can be executed within a short period of time.
- It stores data for temporary use.
Disadvantages
The disadvantages of cache memory are as follows:
- Cache memory has limited capacity.
- It is very expensive.
Primary Memory (Main Memory)
Primary memory holds only those data and instructions on which
computer is currently working. It has limited capacity and data is lost
when power is switched off. It is generally made up of semiconductor
device. These memories are not as fast as registers. The data and
instruction required to be processed reside in main memory. It is
divided into two subcategories RAM and ROM.
Characteristics of Main Memory
- These are semiconductor memories
- It is known as main memory.
- Usually volatile memory.
- Data is lost in case power is switched off.
- It is working memory of the computer.
- Faster than secondary memories.
- A computer cannot run without primary memory.
Secondary Memory
This type of memory is also known as external memory or non-volatile.
It is slower than main memory. These are used for storing
data/Information permanently. CPU directly does not access these
memories instead they are accessed via input-output routines. Contents
of secondary memories are first transferred to main memory, and then CPU
can access it. For example : disk, CD-ROM, DVD etc.
Characteristic of Secondary Memory
- These are magnetic and optical memories
- It is known as backup memory.
- It is non-volatile memory.
- Data is permanently stored even if power is switched off.
- It is used for storage of data in a computer.
- Computer may run without secondary memory.
- Slower than primary memories.
Computer - RAM
RAM(Random Access Memory) is the internal memory of the CPU for
storing data, program and program result. It is read/write memory which
stores data until the machine is working. As soon as the machine is
switched off, data is erased.
Access time in RAM is independent of the address that is, each
storage location inside the memory is as easy to reach as other
locations and takes the same amount of time. Data in the RAM can be
accessed randomly but it is very expensive.
RAM is volatile, i.e. data stored in it is lost when we switch off
the computer or if there is a power failure. Hence a backup
uninterruptible power system(UPS) is often used with computers. RAM is
small, both in terms of its physical size and in the amount of data it
can hold.
RAM is of two types
- Static RAM (SRAM)
- Dynamic RAM (DRAM)
Static RAM (SRAM)
The word
static indicates that the memory retains its contents
as long as power is being supplied. However, data is lost when the
power gets down due to volatile nature. SRAM chips use a matrix of
6-transistors and no capacitors. Transistors do not require power to
prevent leakage, so SRAM need not have to be refreshed on a regular
basis.
Because of the extra space in the matrix, SRAM uses more chips than
DRAM for the same amount of storage space, thus making the manufacturing
costs higher. So SRAM is used as cache memory and has very fast access.
Characteristic of the Static RAM
- It has long life
- There is no need to refresh
- Faster
- Used as cache memory
- Large size
- Expensive
- High power consumption
Dynamic RAM (DRAM)
DRAM, unlike SRAM, must be continually
refreshed in order to
maintain the data. This is done by placing the memory on a refresh
circuit that rewrites the data several hundred times per second. DRAM is
used for most system memory because it is cheap and small. All DRAMs
are made up of memory cells which are composed of one capacitor and one
transistor.
Characteristics of the Dynamic RAM
- It has short data lifetime
- Need to be refreshed continuously
- Slower as compared to SRAM
- Used as RAM
- Lesser in size
- Less expensive
- Less power consumption
Computer -ROM
ROM stands for Read Only Memory. The memory from which we can only
read but cannot write on it. This type of memory is non-volatile. The
information is stored permanently in such memories during manufacture. A
ROM, stores such instructions that are required to start a computer.
This operation is referred to as bootstrap. ROM chips are not only used
in the computer but also in other electronic items like washing machine
and microwave oven.
Following are the various types of ROM
MROM (Masked ROM)
The very first ROMs were hard-wired devices that contained a
pre-programmed set of data or instructions. These kind of ROMs are known
as masked ROMs which are inexpensive.
PROM (Programmable Read only Memory)
PROM is read-only memory that can be modified only once by a user.
The user buys a blank PROM and enters the desired contents using a PROM
program. Inside the PROM chip there are small fuses which are burnt open
during programming. It can be programmed only once and is not erasable.
EPROM(Erasable and Programmable Read Only Memory)
The EPROM can be erased by exposing it to ultra-violet light for a
duration of up to 40 minutes. Usually, an EPROM eraser achieves this
function. During programming, an electrical charge is trapped in an
insulated gate region. The charge is retained for more than ten years
because the charge has no leakage path. For erasing this charge,
ultra-violet light is passed through a quartz crystal window(lid). This
exposure to ultra-violet light dissipates the charge. During normal use
the quartz lid is sealed with a sticker.
EEPROM(Electrically Erasable and Programmable Read Only Memory)
The EEPROM is programmed and erased electrically. It can be erased
and reprogrammed about ten thousand times. Both erasing and programming
take about 4 to 10 ms (milli second). In EEPROM, any location can be
selectively erased and programmed. EEPROMs can be erased one byte at a
time, rather than erasing the entire chip. Hence, the process of
re-programming is flexible but slow.
Advantages of ROM
The advantages of ROM are as follows:
- Non-volatile in nature
- These cannot be accidentally changed
- Cheaper than RAMs
- Easy to test
- More reliable than RAMs
- These are static and do not require refreshing
- Its contents are always known and can be verified
Computer - Motherboard
The motherboard serves as a single platform to connect all of the
parts of a computer together. A motherboard connects CPU, memory, hard
drives, optical drives, video card, sound card, and other ports and
expansion cards directly or via cables. It can be considered as the
backbone of a computer.
Features of Motherboard
A motherboard comes with following features:
- Motherboard varies greatly in supporting various types of components.
- Normally a motherboard supports a single type of CPU and few types of memories.
- Video Cards, Hard disks, Sound Cards have to be compatible with motherboard to function properly
- Motherboards, cases and power supplies must be compatible to work properly together.
Popular Manufacturers
- Intel
- ASUS
- AOpen
- ABIT
- Biostar
- Gigabyte
- MSI
Description of Motherboard
The motherboard is mounted inside the case and is securely attached
via small screws through pre-drilled holes. Motherboard contains ports
to connect all of the internal components. It provides a single socket
for CPU whereas for memory, normally one or more slots are available.
Motherboards provide ports to attach floppy drive, hard drive, and
optical drives via ribbon cables. Motherboard carries fans and a special
port designed for power supply.
There is a peripheral card slot in front of the motherboard using
which video cards, sound cards and other expansion cards can be
connected to motherboard.
On the left side, motherboards carry a number of ports to connect
monitor, printer, mouse, keyboard, speaker, and network cables.
Motherboards also provide USB ports which allow compatible devices to be
connected in plug-in/plug-out fashion for example, pen drive, digital
cameras etc.
Following are few important types of ports:
Features of system software are as follows:
Features of application software are as follows:
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