Internal Hard Drives
An internal hard drive, as the name suggests is found inside the computer. It is the main component of any computing device as it stores all the data, operating system and applications. Laptops have only one hard drive installed in them while desktop computers may have more than one. If required, the number of hard drives may be increased.
In laptops, hard drives with a form factor 1.8” and 2.5” are used, while in desktop computers, form factors 2.5” and 3.5” are used. The storage capacity of internal hard drives varies from 10 GB to 6 TB.
Two connectors are usually required: one for data transmission and one for the power supply.
External Hard Drives
For most laptop users, the storage capacity of an internal hard drive is just not enough. So, an external hard drive is the perfect solution.
External hard drives have 2 connectors, USB 2.0 and Firewire. USB 2.0 connector supports data transfer rate up to 480 MB/s while firewire supports data transfer rate from 400 MB/sec to 800 MB/sec. A major advantage of an external hard drive is the portability due to their smaller size.
RAID (Redundant Array Individual Disks)
RAID is a virtualisation technology that combines many individual hard drives in an array, resulting in a big single storage device. Performance and data transfer rate is increased with the RAID method as many devices process data at the same time. Data is also distributed at the same to all the drives.
The RAID scheme is divided into 6 different levels.
RAID 0:
- Improves performance of W/R operations
- No error detection mechanism
- No fault tolerance
- No data redundancy
- Failure of one disk causes data loss of all disks in array
RAID 1:
- Comprises mirroring (without parity)
- Includes error detection mechanism
- Array works properly as long as a single hard drive is functioning
- Read requested is serviced by the specific disk containing requested data
RAID 2:
- Comprises bit-level striping with hamming-code parity
- Disk rotation of all disks is synchronized and data is striped that each disk has different bit
- This mechanism is no more used
RAID 3:
- Comprises byte-level striping
- Disk rotation of all disks is synchronized and data is striped that each disk has different bit
- This technology is not used in commercial industry now
RAID 4:
- Comprises block-level striping and dedicated parity
- This mechanism is now replaced by RAID-DP with two parity disks
- RAID-DP is the proprietary implementation of RAID 4
RAID 5:
- Block-level striping and distributed parity
- It requires at least one disk working to operate
- On failure of a single disk data is never lost
- It requires at least 3 disks in array
RAID 6:
- Block level striping
- Double distributed parity
- Tolerance up to 2 failure drives
- This mechanism is used because of double parity
- Problems in RAID 5 are covered in RAID 6
Types of Hard Drives
- PATA (Parallel ATA )
- SATA (Serial ATA)
- SCSI (Small Computer System Interface)
- SSD (Solid State Drives)
PATA
Parallel ATA is a connector used for hard drives to the motherboard of a computer. It is based on the parallel signaling technology. PATA connectors are used in Integrated Drive Electronics (IDE Hard Drive). This connector type was introduced in 1980’s and originally it was called ATA. Later on in 2003 it was renamed as PATA.
Data Transfer Rate of Different Modes
| Mode |
Mode No. |
Transfer Rate(Max) |
Cycle Speed |
|
PIO |
0 |
3.3 Mbps |
600 ns |
|
1 |
5.2 Mbps |
383 ns |
|
|
2 |
8.3 Mbps |
240 ns |
|
|
3 |
11.1 Mbps |
180 ns |
|
|
4 |
16.7 Mbps |
120 ns |
|
|
Form Factors and Single-Word DMA |
0 |
2.1 Mbps |
960 ns |
|
1 |
4.2 Mbps |
480 ns |
|
|
2 |
8.3 Mbps |
240 ns |
|
|
Multi-Word DMA |
0 |
4.2 Mbps |
480 ns |
|
1 |
13.3 Mbps |
150 ns |
|
|
2 |
16.7 Mbps |
120 ns |
|
|
3 |
20 Mbps |
100 ns |
|
|
4 |
25 Mbps |
80 ns |
Specifications of PATA SSDs Products
| Product No. |
R/W Rate |
Storage Capacity |
Form Factor |
Temperature |
|
MSPR 3610 |
1120/60 MB/s |
4/8/16 GB |
2.5″ |
-40℃~+85℃ |
|
GTR-P |
100/100 MB/s |
32/64/128 GB |
2.5″ |
-40℃~+85℃ |
|
STRP-25 |
90/100 MB/s |
16/32/64/128/256 GB |
2.5″ |
-40℃~+85℃ |
|
STMP-25 |
90/100 MB/s |
32/64/128/256 GB |
2.5″ |
0℃~+70℃ |
|
MSP 3610 |
110/60 MB/s |
4/8/16/32/64/128 GB |
2.5″ |
0℃~+70℃ |
|
STP-25 |
90/100 MB/s |
16/32/64/128/256 GB |
2.5″ |
0℃~+70℃ |
Advantages:
- Two devices per PATA cable
- Cheaper than all other hard drive types
Disadvantages:
- Short cable length (max. length is 18 inches)
- Low data transfer rate
Recommendation:
PATA drives are used in Pentium 1,2,3,4 computers. These computers are rare now. Product numbers MSPR 3610 and GTR-P are best to be used for office usage, while all other products are best for home PCs.
SATA
Serial ATA is a connector introduced to replace its predecessor the PATA connector. SATA uses low-voltage signaling technology which requires low power and cooling. Only 0.7 volts are required to operate SATA drives.
SATA connectors are smaller than PATA connectors. In PATA connectors 40 pins are used while in SATA connectors only 7 pins are used for transmitting data. SATA cables are available in lengths up to 1 metre and are used for connecting the motherboard to one hard drive.
In SATA drives, a wafer-type power connector is used. It has 15 pins in its connector.
SATA Revisions
| Revision |
Uncoded Data Transfer Rate |
Native Data Transfer Rate |
|
1.0 |
150 Mbps |
1.5 GB/s |
|
2.0 |
300 Mbps |
300 GB/s |
|
3.0 |
600 Mbps |
6 GB/s |
|
3.1 |
600 Mbps |
6 GB/s |
|
3.2 |
1969 Mbps |
16 GB/s |
Advantages:
- Increased data transfer rate
- Less number of pins in connectors
- Increased cable length
- Supports more devices than PATA
- Available in larger capacity than PATA drives
Disadvantages:
- Connects one drive per cable
- Specific drivers are required for SATA drives to operate on computers
- Not supported in older computer models without addition of extra components
Recommendation:
SATA versions 1.0 and 2.0 are best for home PCs installation while versions 3.0, 3.1 and 3.2 are ideal for commercial PCs installations because of their high data transfer rate.
SCSI
SCSI is a set of standards of connectors used for connecting peripheral devices with the computer. SCSI standard includes protocols, commands, electrical and optical connectors. They are mostly used for connecting tape drives and hard drives with computer servers and for industrial use.
Advantages:
- Increased data transfer rate than SATA drives
- Can connect more than one devices through one channel
- Wide range of applications supported
- Reliable than SATA and PATA drives
Disadvantages:
- Increased cost
- Greater RPM speed, that creates more noise
Recommendation:
SCSI hard drives are ideal for Offices and Industries but is not recommended for home PCs due to their high costs.
SSD
Solid State drives do not have any moving disc for storing data. These drives use flash chips as storing element. New connectors are created for SSDs for better speed. SSD is preferred for applications where fast data access is required. Due to no presence of any moving element SSD drives are indestructible.
- For notebooks maximum storage capacity is 512 GB and for desktops max storage capacity is 1 TB.
- Average Boot time on an operating system is 22 seconds.
- Price is about £0.35 when purchasing SSD of 1 TB storage capacity.
- File transfer speed varies from 200 MB/s to 550 MB/sec depending upon host machine.
Host Interfaces Types and Data Rate
| Host Interface Type |
Data Rate |
|
SAS |
>3.0 Gbps |
|
SATA |
>2.0 Gbps |
|
Optical Fibre Channel |
>200 Mbps |
|
PCI Express |
>2.0 Gbps |
|
USB |
>1.5 Mbps |
|
PATA |
>26.4 Mbps |
Advantages:
- Fast boot speed
- No noise created
- Available in smaller sizes
- Longer data life
- Consumes less power
- Generates less heat
Disadvantages:
- Very expensive that SCSI and SATA drives
- Low storage capacity
- Slow data write and read speed
- Inability to recover data
Recommendation:
SSD hard drives are only suitable for installation in large size offices having greater budget for IT hardware because of their very high costs.
Form Factors and Storage Capacities of Hard Drives
| Form Factor |
Height (mm) |
Length (mm) |
Width (mm) |
Capacity (max) |
Platters |
Storage per Platter |
|
1.8” |
5 – 8 |
71 |
54 |
320 GB |
2 |
220 |
|
2.5” |
5 – 15 |
100 |
69.85 |
2 TB |
4 |
500 |
|
3.5” |
19 – 25.4 |
146 |
101.6 |
6 TB |
5 – 7 |
1200 |
Conclusion
For small and medium size businesses HDDs are recommended because of their low costs. SSDs are best choice because of their low form factor, no noise, better speed and fragmentation features. PATA drives are no more used as they were designed for the older models of computers. SATA drives are best for home PCs.
