Section 3 - Hardware

3.1.1 - Types of Memory and Storage

Memory: it is the internal devices which a computer can access directly

Storage Devices:
1. Used to store data permanently and can be changed
2. Larger than internal memory
3. Can be removable

Memory and storage devices can be split up into three distinct groups:
● Primary memory
● Secondary storage
● Off-line storage

Primary Memory

Primary Memory: part of the computer memory that can be accessed from the CPU. Contains
RAM and ROM chips

Random Access Memory (RAM): It is volatile/temporary memory. It can be written to or read

from and the contents of the memory can be changed.

- The larger the size of the RAM, the faster it will operate
- RAM never runs out of memory, it continues to operate but gets slower and slower
- Its main drawback is its volatility

Read Only Memory (ROM):

- They are non-volatile/permanent memories
- Often used to store start-up instructions when the computer is first switched on
- Data or contents of a ROM chip can only be read; they cannot be changed

RAM ROM

Temporary memory device Permanent memory device

Volatile memory Non-volatile memory

Can be written to or read from Data can’t be altered

Dynamic RAM (DRAM): Each dynamic RAM chip consists of a number of transistors and
capacitors.

- Capacitor: This holds the bits of information ( 0 or 1 )

- Transistor: This acts like a switch; it allows the chip control circuitry to read the capacitor
or change the capacitor’s value
- This type of RAM needs to be constantly refreshed

Static RAM (SRAM): This type of memory doesn’t need to be constantly refreshed. It makes use
of ‘flip flops’ which hold each bit of memory.

- SRAM are much faster than DRAM when it comes to data access
- SRAM is used when absolute speed is essential

Advantages of DRAM over SRAM:

● Much less expensive to manufacture
● Consume less power
● Have higher storage capacity

DRAM SRAM

Needs to be constantly refreshed Doesn’t need to be constantly refreshed

Less expensive to manufacture than SRAM Has faster data access time than DRAM

Consists of transistors and capacitors Uses flip-flops to hold each bit of memory

Programmable Read-Only Memory (PROM): it is a type of ROM chip that can be altered once.
This is because the PROM writer alters cells by burning the fuses. Used in RFID tags

Erasable Programmable Read-Only Memory (EPROM): it is a type of ROM chip that uses
floating gate transistors and capacitors
Embedded Systems: this involves putting microprocessors in devices, which can then be
controlled by a web-enabled device

Pros Cons

Small in size Difficult to upgrade devices

Low cost to make Devices accessed over the internet are

vulnerable to hackers

Consumes very little power Due to difficulty in upgrading, devices are

thrown away

Secondary Storage

Secondary Storage Devices: devices not accessible by CPU. They are non-volatile and larger
than primary memory

Hard Disk Drives (HDD): It is the most common method used to store data on a computer.

- The data is stored in a digital format on the magnetic surfaces of the disks
- The hard disk drive will have a number of platters which can spin at about 7000 times a
second
- A number of read-write heads can access all of the surfaces in the disk drive

- Each platter will have two surfaces which can be used to store the data
- Data is stored on the surface in sectors and tracks
- A sector on a given track will contain a fixed number of bytes

Latency: The time it takes for a specific block of data on a data track to rotate around to the
read-write head.

( Many applications require the read-write heads to constantly seek for the correct blocks of
data; this means a large number of head movements. The effects of latency then become very
significant )
Solid-State Drives (SSD): This drive has no moving parts and all data is retrieved at the same
rate. They don’t rely on magnetic properties.

- SSD devices store data by controlling the movements of electrons within NAND chips
- It is a non-volatile rewritable memory

Some SSD devices use Electronically Erasable Programmable Read-Only Memory (EEPROM)
technology. The main difference is the use of NOR chips rather than NAND.

EEPROM allows data to be read or erased in single bytes at a time. Use of NAND only allows
blocks of data to be read or erased.

Benefits of SSD over HDD:

● They are more reliable and considerably lighter
● They have a lower power consumption
● They run much cooler than HDDs
● They have no moving parts, they are very thin

Off-Line Storage

Offline Storage:
- CD/DVD/DVD-RAM (optical storage systems)
- Blu-Ray Discs (optical storage systems)
- USB flash memory/ memory sticks/ SD-XD cards (solid state storage systems)
- Removable/External hard disk drives (magnetic storage systems)

CD/DVD Discs:
- Laser light is used to read data and to write data in the surface of the disc
- They use a thin layer of metal alloy or light-sensitive organic dye to store the data
- The data is stored in ‘pits’ or ‘bumps’ on the spiral track

DVD technology uses dual-layering which increases the storage capacity. There are two
individual recording layers. Two layers of a standard DVD are joined together with a transparent
spacer, and a very thin reflector is sandwiched between the two layers.

DVD-RAM:
- Instead of single, spiral track, they use a number of concentric tracks
- Use of concentric tracks allow simultaneous read and write operations to take place
- They allow numerous read and write operations and have a great longevity, making it
ideal for archiving
Blu-Ray Discs:
- A blue laser is used to carry out read and write operations
- A blue laser means the ‘pits’ and ‘bumps’ are much smaller, therefore allowing more data
to be stored
- Blue-Ray discs automatically come with a secure encryption system

USB Flash Memories:

- They are small, lightweight devices, making them ideal for transferring files across
computers
- Digital Cameras use XD (eXtreme Digital) or SD (Secure Digital) cards
- Each memory card is made up of NAND chips, and they have no moving parts
- Solid-state memories must be removed from a device after being made safe

Removable Hard Disk Drive: They are essentially HDD but can be connected to the computer
using one of the USB ports.