Computer storage devices

Computer Storage Devices
11/6/2014
Tallal Jamshed

Contents
1. Primary storage...........................................................................................................................3
1.1 ROM (Read Only Memory) ...................................................................................................4
1.1.1 PROM (Programmable Read Only Memory) ...................................................................4
1.1.2 EPROM (Erasable Programmable Read Only Memory) ....................................................4
1.1.3 EEPROM (Electrically Erasable Programmable Read Only Memory)..................................4
1.2 RAM (Random Access Memory) ............................................................................................5
1.1.1 DRAM (Dynamic Random Access Memory) ....................................................................5
1.1.2 SRAM (Static Random Access Memory)..........................................................................6
2. Secondary storage .......................................................................................................................6
3. Removable Storage Media ...........................................................................................................8
Table of figures
Figure 1 ROM (Read Only Memory) .....................................................................................................4
Figure 2 RAM (Random Access Memory)..............................................................................................5
Figure 3 System DRAM........................................................................................................................5
Figure 4 Smaller SRAM ........................................................................................................................6
Figure 5 IDE HDD (above) SATA HDD (below)........................................................................................7
Figure 6 SSD (Solid State Derive) ..........................................................................................................7
Figure 7 Optical Disks ..........................................................................................................................7
Figure 8 USB storage ...........................................................................................................................8
Figure 9 Memory Card ........................................................................................................................8
Figure 10 External Hard disk ................................................................................................................9

Computer Storage Devices
Without a significant amount of memory, a computer would merely be able to perform fixed
operations and immediately output the result without storing them therefore some kind of
memory is placed in the computer to store instructions for processor and data to be processed
and also the output results for future use.
There are three types of storage devices in computer
1. Primary storage
2. Secondary storage
3. Removable storage
1. Primary storage
Primary storage, often referred to simply as memory, is the only one directly accessible to the
CPU. The CPU continuously reads instructions stored there and executes them as required. Any
data actively operated on is also stored there in uniform manner.
There are two types of primary storage
1. ROM (Read Only Memory)
2. RAM (Random Access Memory)

1.1 ROM (Read Only Memory)
Figure 1 ROM (Read Only Memory)
In this type of memory the information is stored permanently; it is not lost after the system shuts
down. The advantage of using this memory is that there are some complex functions like
translators that are used repeatedly. These functions are permanently stored in the ROM and these
instructions are hard wired in ROM so the execution is very fast.
There are further three types of ROM.
1.1.1 PROM (Programmable Read Only Memory)
In this the ROM is programmable but only once. PROM is produced blank. It is programmed only
later. The advantage of using PROM is that a company can change the program it is going to store
whenever they want without loss of hardware.
1.1.2 EPROM (Erasable Programmable Read Only Memory)
This type of PROM can be erased and reprogrammed a number of times. Here the chip that holds
the memory is exposed through a glass widow. A strong UV light of a particular frequency if shined
through this glass window will erase the EPROM
1.1.3 EEPROM (Electrically Erasable Programmable Read Only Memory)
This PROM can be reprogrammed under software control. Actually the design of this ROM is like
that it can be programmed by giving particular programming voltage that erases the previous
program then it can be reprogrammed normally

1.2 RAM (Random Access Memory)
Figure 2 RAM (Random Access Memory)
Unlike the ROM this is type of memory is volatile and can be erased by disconnecting power going
to it. Data can be written to it and may be retrieved from it according to the address given. This
type of memory is fast and a CPU access RAM to retrieve data and instruction as fast as possible
RAM has two further types
1.1.1 DRAM (Dynamic Random Access Memory)
Figure 3 System DRAM
DRAM is a type of RAM which cannot retain its data for a long time. It is made up of small capacitors
which stores bits in form of electric charge. Due to leakage in capacitors they cannot maintain
charge for long time for that reason they are continuously needed to be refreshed with the help of

some refreshing circuit. These kinds of RAMs are cheap but bulky and can only be used as bigger
system RAMs connected on mother bored
1.1.2 SRAM (Static Random Access Memory)
Figure 4 Smaller SRAM
SRAM is a semiconductor memory which can retain its data for long time without the need to
refresh continuously they store data on semiconductor bi -stable latching circuitry to store each bit.
This kind of RAM is very costly but small in size and very fast that’s why they are used in CPU as
cache memory
2. Secondary storage
Secondary storage , is not directly accessible by the CPU. The computer usually uses its input
output busses to access secondary storage and transfers the desired data using primary storage.
Secondary storage does not lose the data when the device is powered down—it is non-volatile. it
is typically less expensive than primary storage. Computer systems have more secondary
storage than primary storage and data is kept for a longer time there. In modern computers, hard
disk drives (HDD) are usually used as secondary storage.
There are following types of hard disk drives

2.1 Hard disk drives (HDD)
Figure 5 IDE HDD (above) SATA HDD (below)
Hard disk drive is a magnetic device used to store data on the surface of metallic disks with magnetic
surfaces. Data can be written and read on it unlimited times. It is slower then RAM but can store
large amounts of data on both sides of magnetic disk it is also heavy and big that’s why it is
connected with wires on mother board
2.2 Solid State Drives (SSD)
Figure 6 SSD (Solid State Derive)
A solid state derive is a new and improved form of storage used instead of hard disks in computers.
It is made up of semiconductor storage technology used in smaller more familiar memory cards used
in cell phones it is incredibly light in wait and small in size it is also fast but very costly that’s why it is
not very popular in commercial computers
2.3 Optical disks
Figure 7 Optical Disks

An optical disk is commonly known as CD or DVD. This is another kind of storage technology which
uses laser technology to make patterns on certain light sensitive disks. A CD is a little old fashioned
device and it can only store data of upto 700 MBs where as the mostly used DVD now a days can
store upto 8.5 GBs of data
All the optical disk types are as follows
 CD (compact disks) upto 700 MBs storage
 DVD (digital video disk) upto 8.5 GBs storage
 HD DVD (high definition digital video disk) upto 51 GBs storage
 Blu-ray Disk upto 400 GBs storage
3. Removable Storage Media
Figure 8 USB storage
Figure 9 Memory Card

Figure 10 External Hard disk
Removable storage media is that type of storage devices which can be used to store data
permanently but they are portable. The can be connected to computer system to read or write data
then it can be detached from system to transfer it to other system or just for storage means
Removable media include
 Flash derives or commonly known as USB
 Optical discs
 Magnetic tapes
 External hard disk derives

Computer storage devices

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Computer storage devices