Basics of computer hardware for beginners

1. PC HARDWARE , MAITENANCE
AND ADMINISTRATION - THEORY

2. Week 6:
Content:
• Memory- Memory Units (B, KB,
MB,GB, TB),
• Memory locations and address
space,
• Access methods, Memory
Classification.
• Main memory Types and Features.
• Auxiliary memory - Types and
features. Memory modules.
PC HARDWARE MANITENACE AND ADMINISTRATION - THERORY

3. Memory Memory Units (B, KB, MB,GB, TB)
Computer memory is any physical device capable of storing
information temporarily, like RAM (random access
memory), or permanently, like ROM (read-only memory).
Memory devices utilize integrated circuits and are used by
operating systems, software, and hardware.

4. S.No. Unit & Description
1 Bit (Binary Digit)
A binary digit is logical 0 and 1 representing a passive or an active state of a component in an
electric circuit.
2 Nibble
A group of 4 bits is called nibble.
3 Byte
A group of 8 bits is called byte. A byte is the smallest unit, which can represent a data item or a
character.
4 Word
A computer word, like a byte, is a group of fixed number of bits processed as a unit, which
varies from computer to computer but is fixed for each computer.
The length of a computer word is called word-size or word length. It may be as small as 8 bits or
may be as long as 96 bits. A computer stores the information in the form of computer words.
Memory Units (B, KB, MB,GB, TB)

5. S.No. Unit & Description
1
Kilobyte (KB)
1 KB = 1024 Bytes
2
Megabyte (MB)
1 MB = 1024 KB
3
GigaByte (GB)
1 GB = 1024 MB
4
TeraByte (TB)
1 TB = 1024 GB
5
PetaByte (PB)
1 PB = 1024 TB
The following table lists some higher storage units

6. Memory locations and address space.
• Memory consists of many millions of storage cells (flip-flops).
• Each cell can store a bit of information i.e. 0 or 1 (Figure).
• Each group of n bits is referred to as a word of information, and n is called the word
length.
• The word length can vary from 8 to 64 bits.
• A unit of 8 bits is called a byte.
• Accessing the memory to store or retrieve a single item of information (word/byte)
requires distinct addresses for each item location. (It is customary to use numbers from 0
through 2ˆk-1 as the addresses of successive-locations in the memory).
• If 2ˆk = no. of addressable locations; then 2ˆk addresses constitute the address-space of
the computer. For example, a 24-bit address generates an address-space of 2ˆ24
locations (16 MB).

9. BYTE-ADDRESSABILITY
A byte is always 8 bits, but the word length typically ranges from 16
to 64 bits.
• In byte-addressable memory, successive addresses refer to
successive byte locations in the memory.
• Byte locations have addresses 0, 1, 2. . . . .
• If the word-length is 32 bits, successive words are located at
addresses 0, 4, 8. . with each word having 4 bytes.

10. Memory Access Method
Data need to be accessed from the memory for various purposes.
There are several method to access memory as listed below:
• Sequential access
• Direct access
• Random access
• Associative access

11. Sequential Access Method
In sequential memory access method, the memory is accessed in linear
sequential way.
The time to access data in this type of method depends on the location of the
data.
Example of sequential access: Magnetic disks, magnetic tapes, optical memory
use sequential access method.

13. Random Access Method
• In random access method, data from any location of the memory can be
accessed randomly.
• The access to any location is not related with its physical location and is
independent of other locations.
• There is a separate access mechanism for each location.
Example of random access: Semiconductor memories like RAM, ROM use
random access method.

15. Direct Access Method
• Direct access method can be seen as combination of sequential access
method and random access method.
• Magnetic hard disks contain many rotating storage tracks.
• Here each tracks has its own read or write head and the tracks can be
accessed randomly. But access within each track is sequential.
Example of direct access: Memory devices such as magnetic hard disks.

17. Associative Access Method
• Associative access method is a special type of random access method.
• It enables comparison of desired bit locations within a word for a specific
match and to do this for all words simultaneously.
• Thus based on portion of word's content , word is retrieved rather than its
address.
Example of associative access: Cache memory uses associative access method.

19. Memory Classification.
Based on the type of use and feature memory unit of computer is categorized as:
• Primary Memory - It is also known as internal memory or Main memory.
• Secondary Memory - It is also known as auxiliary memory.

20. Main memory Types and Features.
• Main memory or Primary memory refers to a set of memory units within
the computer, CPU has direct access to and it stores instruction and data
needed for processing by CPU.
• Primary memory stores the intermediate results and final results of the
processing before it is stored in the permanent storage.
• Some of this memory is volatile i.e. contents stored will get erased if power
is switched off and some of them are non-volatile i.e. contents cannot be
erased.

22. Random Access Memory (RAM) –
• It is also called read-write memory or the main memory or the
primary memory.
• The programs and data that the CPU requires during the
execution of a program are stored in this memory.
• It is a volatile memory as the data is lost when the power is
turned off.
• RAM is further classified into two types- SRAM (Static Random
Access Memory) and DRAM (Dynamic Random Access
Memory).

24. Read-Only Memory (ROM)
• Stores crucial information essential to operate the system, like the program
essential to boot the computer.
• It is not volatile.
• Always retains its data.
• Used in embedded systems or where the programming needs no change.
• Used in calculators and peripheral devices.
• ROM is further classified into four types- MROM, PROM, EPROM, and
EEPROM.

25. Types of Read-Only Memory (ROM)
• PROM (Programmable read-only memory) – It can be programmed by the
use. Once programmed, the data and instructions in it cannot be changed.
• EPROM (Erasable Programmable read-only memory) – It can be
reprogrammed. To erase data from it, expose it to ultraviolet light. To
reprogram it, erase all the previous data.
• EEPROM (Electrically erasable programmable read-only memory) – The data
can be erased by applying an electric field, with no need for ultraviolet light.
We can erase only portions of the chip.
• MROM(Mask ROM) – Mask ROM is a kind of read-only memory, that is
masked off at the time of production. Like other types of ROM, mask ROM
cannot enable the user to change the data stored in it. If it can, the process
would be difficult or slow.

26. Types of Read-Only Memory (ROM)
• PROM (Programmable read-only memory) – It can be programmed by the
user. Once programmed, the data and instructions in it cannot be changed.
• EPROM (Erasable Programmable read-only memory) – It can be
reprogrammed. To erase data from it, expose it to ultraviolet light. To
reprogram it, erase all the previous data.
• EEPROM (Electrically erasable programmable read-only memory) – The data
can be erased by applying an electric field, with no need for ultraviolet light.
We can erase only portions of the chip.
• MROM(Mask ROM) – Mask ROM is a kind of read-only memory, that is
masked off at the time of production. Like other types of ROM, mask ROM
cannot enable the user to change the data stored in it. If it can, the process
would be difficult or slow.

28. Auxiliary memory
Definition -: Secondary memory is the secondary storage device of the computer
which is used to store the program in the computer and the output obtained
from the execution of the program permanently.
• Secondary memory is a non-volatile memory in which all the data and
information stored in the computer remains saved even after the computer is
turned off.
• It is not directly accessed by the CPU like primary memory.
• The data from the secondary memory is first loaded into RAM (Random
Access Memory) or primary memory and then sent from the primary memory
to the processor (CPU) to read and update the data.

29. • Secondary memory is a permanent storage memory which is much slower and cheaper
than primary memory.
• Secondary memory is also known as external memory or auxiliary storage, inside which
data can be stored in gigabytes and terabytes.
Examples of Secondary Memory –:
• Magnetic Tape
• Magnetic Disk
• Floppy Disk
• Hard Disc
• Compact Disc
• Pen Drive
• Flash Drive
• SSDs
• Optical disk drives (CD or DVD)

30. Types and features.
Types of Secondary Memory
• Secondary memory is of two types depending on whether it is part of CPU or not –
1. Fixed Storage Device
2. Removable Storage Device
1. Fixed Storage Device
• Fixed storage media is an internal storage media like a hard disk that is fixed inside the
computer.
• Fixed storage is an internal media device known as Fixed Disk Drives or Hard Drives.
• Fixed storage devices are not really completely fixed, they can be removed for system
repair, maintenance, and upgrade, etc.
• But it cannot be opened without a toolkit and if it needs to be opened for upgrade or
any other work then this work is done by an engineer

31. Types of fixed storage:
• Internal flash memory (rare)
• SSD (solid-state disk) units
• Hard disk drives (HDD)
2. Removable Storage Device
• Such storage devices that are outside the computer and which can be removed from the
computer anytime, by connecting with the computer, are called Removable Secondary Storage
devices.
• Removable storage is an external media device known as removable disk drives or external
drives.
• Removable Storage Device is a storage device that can be removed from the computer system
while the system is running.
• Examples of removable devices include CDs, DVDs, and Blu-ray disk drives, as well as diskette
and USB drives.
• Removable storage devices make it easy for the user to transfer data from one computer
system to another.

32. Types of Removable Storage:
• Optical discs (CDs, DVDs, Blu-ray discs)
• Memory cards
• Floppy disks
• Magnetic tapes
• Disk packs
• Paper storage (punched tapes, punched cards)

33. Features of Secondary Memory
• Secondary memory is also known as a backup memory.
• It is a non-volatile memory.
• The data is permanently stored in the secondary memory.
• It is used to store data and programs in the computer.
• Computer can also run without secondary memory.
• Secondary memory is slower than primary memory.
• It is cheaper than primary memory.
• It consists of optical and magnetic memory for storing data.
• This is an external memory.

34. Memory modules.
• A memory module is another name for a RAM chip. It is often used as a general term
used to describe SIMM, DIMM, and SO-DIMM memory.
• While there are several different types of memory modules available, they all serve the
same purpose, which is to store temporary data while the computer is running.
• Memory modules come in different sizes and have several different pin configurations.
• For example, the original SIMMs had 30 pins (which are metal contacts that connect to
the motherboard).
• However, newer SIMM chips have 72 pins. DIMMs commonly come in 168-pin
configurations, but some DIMMs have as many as 240 pins.
• SO-DIMMs have a smaller form factor than standard DIMM chips, and come in 72-pin,
144-pin, and 200-pin configurations.