Types of Storages - Computer Architecture Topic

 

Types of Storage

Local Storage Options

1. External Hard Drive

These are hard drives similar to the type that is installed within a desktop computer or laptop computer. The difference being that they can be plugged in to the computer or removed and kept separate from the main computer. They typically come in two sizes.

Desktop External Hard drive: Uses a 3.5 inch hard drive similar to that used in desktop computers.

Portable External Hard drive: Uses a 2.5 inch hard drive similar to that used in laptops.

Desktop External Hard Drives are generally cheaper than Portable External Hard Drives for the same storage space. Desktop External Hard Drives and usually faster and more robust.

Capacity: 160GB to 3TB (approx. 3000GB)

Connection: Most common connections to the computer are through a USB 2.0 or USB3.0 connection. May also be available in a SATA or eSATA connector

Advantages:

• Very good option for local backups of large amounts of data.
• The cheapest storage option in terms of dollars per GB. Very reliable when handled with care

Disadvantages:

• Can be very delicate. May be damaged if dropped or through electrical surge

 

2. Solid State Drive (SSD)

Solid State Drives look and function similar to traditional mechanical/ magnetic hard drives but the similarities stop there. Internally, they are completely different. They have no moving parts or rotating platers. They rely solely on semiconductors and electronics for data storage making it a more reliable and robust than traditional magnetic. No moving parts also means that they use less power than traditional hard drives and are much faster too.

With the prices of Solid State Drives coming down and is lower power usage, SSD’s are used extensively on laptops and mobile devices.  External SSD’s are also a viable option for data backups.

Capacity: 64GB to 256GB

Connections: USB 2.0/3.0 and SATA

Advantages:

• Faster read and write performance
• More robust and reliable than traditional magnetic hard drives
• Highly portable. Can be easily taken offsite

Disadvantages:

• Still relatively expensive when compared to traditional hard drives
• Storage space is typically less than that of traditional magnetic hard drives.

 

3. Network Attached Storage (NAS)

NAS are simply one or more regular IDE or SATA hard drives plugged in an array storage enclosure and connected to a network Router or Hub through a Ethernet port.  Some of these NAS enclosures have ventilating fans to protect the hard drives from overheating.

Advantages:

• Very good option for local backups especially for networks and small businesses.
• As several hard drives can be plugged in, NAS can hold very large amounts of data
• Can be setup with Redundancy (RAID) increasing the reliability and/ or read and write performance. Depending on the type of RAID level used, the NAS can still function even if one hard drive in the RAID set fails. Or two hard drives can be setup to double the read and write speed of single hard drive.
• The drive is always connected and available to the network making the NAS a good option for implementing automated scheduled backups.

Disadvantages:

• Significantly more expensive than using single External Hard Drives
• Difficult to bring offsite making it very much a local backup hence still susceptible to some events   like theft and floods, fire etc

 

4. USB Thumb Drive or Flash Drive

These are similar to Solid State Drives except that it is much smaller in size and capacity. They have no moving parts making them quite robust. They are extremely portable and can fit on a keychain.  They are Ideal for backing up a small amount of data that need to be brought with you on the go.

Capacity: 4GB to 64GB

Advantages:

• The most portable storage option. Can fit on a keychain making it an offsite backup when you bring it with you.
• Much more robust than traditional magnetic hard drives

Disadvantages:

Relatively expensive per GB so can only be used for backing up a small amount of data

 

5. Optical Drive (CD/ DVD)

CD’s and DVD’s are ideal for storing a list of songs, movies, media or software for distribution or for giving to a friend due to the very low cost per disk. They do not make good storage options for backups due to their shorter lifespan, small storage space and slower read and write speeds.

Capacity CD: 650MB to 900MB

Capacity DVD: 4.7GB to 17.08GB

Advantages:

• Low cost per disk

Disadvantages:

• Relatively shorter life span than other storage options
• Not as reliable as other storage options like external hard disk and SSD. One damaged disk in a backup set can make the whole backup unusable.

 

Remote Storage Options

6. Cloud Storage

Cloud storage is storage space on commercial data center accessible from any computer with Internet access. It is usually provided by a service provider. A limited storage space may be provided free with more space available for a subscription fee.  Examples of service providers are Amazon S3, Google Drive and Sky Drive etc.

Advantages:

• A very good offsite backup. Not affected by events and disasters such as theft, floods, fire etc

Disadvantages:

• More expensive than traditional external hard drives. Often requires an ongoing subscription.
• Requires an Internet connection to access the cloud storage.
• Much slower than other local backups

 

 

Q.2 Buses: Connecting I/O to Processor and Memory.

Input/output

Buses: Connecting I/O to Processor and Memory

• A bus is a shared communication link
• It uses one set of wires to connect multiple subsystems

Sometimes shared bus with memory, sometimes a separate I/O bus

 
 

Advantages

• Versatility:
• New devices can be added easily
• Peripherals can be moved between computer

Systems that use the same bus standard

• Low Cost:
• A single set of wires is shared in multiple ways

Disadvantages

• It creates a communication bottleneck
• The bandwidth of that bus can limit the maximum I/O throughput
• The maximum bus speed is largely limited by:
• The length of the bus
• The number of devices on the bus
• The need to support a range of devices with:
• Widely varying latencies
• Widely varying data transfer rates

 

Delegating I/O Responsibility from the CPU: DMA

 

• Direct Memory Access (DMA):
• External to the CPU
• Act as a maser on the bus
• Transfer blocks of data to or from memory without CPU intervention

  
 
Block Diagram of a DMA Controller

Sequence of operations - Input:

1.     CPU loads registers - Address, Count and Device

2.     CPU Sets Status to Input

3.     Controller asks for bus

4.     Gets bus - does read from device, puts Address on the bus, does write to memory and decrements count.

Repeat 4 until count=0

5.     Interrupt CPU to signal end of transfer

 Output is similar but status is set to Output and data is read from memory and written to the output device.