Primary Storage Device

1. Storage Devices
Primary Storage
Devices

2. Categories of Storage
Storage
Computer
Primary
ROM
Permanent
RAM
Temporary
Secondary
Magnetic
Permanent
Optical
Permanent
Circuit
Permanent

3. Primary Storage Devices
• ROM – Read Only Memory
When a computer is made basic input/output
instructions are placed on ROM chips. These
instructions can be read but not changed and are
available every time the computer is switched on.
(ROM
chips store basic start-up information for a computer)
ROM CHIP

4. Primary Storage Devices
• EPROM – Erasable-Programmable-Read Only Memory
Another variation of ROM which can be bought
programmed and eased as desired, by the user.
EPROM is eased by exposing the chip to a strong
source of ultra-violet light

5. Primary Storage Devices
• PROM – Programmable Read Only Memory
This is a variation of ROM in which the user can buy a ROM chip and
program it. Like ROM once programmed the contents cannot be
changed.

6. RAM CHIP
Primary Storage Devices
• RAM – Random Access Memory
Holds temporary operating instructions for the computer, its programs and
data. The CPU get the instructions to do its job from RAM/Main Memory.
Advantage
Data on RAM chips can be access immediately by
the CPU.
Disadvantage
RAM is volatile, i.e., the data is lost when the computer
losses power or malfunctions

7. Primary Storage Devices
• Buffer Memory - A temporary storage area, usually in RAM. The
purpose of most buffers is to act as a holding area, enabling the CPU
to manipulate data before transferring it to a device. Modern
printers come with buffers that store information to be printed while
one page is being printed the others are in the buffer memory waiting
on their turn. Buffer is a temporary block of memory that is waiting
either to be processed or outputted.

8. Primary Storage Devices
• Cache Memory - A high speed storage mechanism, either a reserved
section of main memory or an independent high speed storage device.
There are two types of caching, memory caching and disk caching.
Memory cache is a portion of RAM made with faster SRAM instead of
Slower DRAM. Cache stores frequently accessed data hence this allows the
faster SRAM to be used in accessing repeatedly needed data making
memory access faster.
• Types of Cache
• L1- built directly in the processor chip. Usually has a very small capacity, ranging
from 8kb to 128kb. The core common sizes for PC’s are 32kb to 64kb.
• L2- slightly slower than L1 but has a higher storage capacity, ranging from 64kb to
16Mb.
• L3- built on the motherboard, located between the processor and RAM

9. • Virtual memory - Virtual memory is hard disk space used as if it were RAM.
Hybrid Memory
• EEPROM – Electronically Erasable Programmable Read Only Memory, uses
electrical signals to erase and write data to the memory chip.
• Flash drive and memory cards – uses electrical signals to erase and write
data to the memory chip. Flash and cards are used mainly for secondary
storage
Primary Storage Devices