12. How it works

The CPU sits in the motherboard as the central unit. All of the other hardware components and programs installed on the system must go through the CPU before their function can be carried out. The CPU's job function is important and enormous in scale. When a function, program or piece of data is called, the CPU pulls it from Random Access Memory (RAM) and any other hardware in order to process it. The CPU then reads the instructions associated to the task before sending it back to RAM. The instructions that the CPU receives pertains to calculations and data transportation. The system bus is the trail that the data must travel before it is executed. It is the CPU's job to make sure that the data is guided through the system bus to be processed by the CPU and then on to the next step. With every stop on the system bus, the CPU makes sure that the data gets there in the correct order.

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16. Random and sequential access to data

Comparing random versus sequential operations is one way of assessing application efficiency in terms of disk use. Accessing data sequentially is much faster than accessing it randomly because of the way in which the disk hardware works. The seek operation, which occurs when the disk head positions itself at the right disk cylinder to access data requested, takes more time than any other part of the I/O process. Because reading randomly involves a higher number of seek operations than does sequential reading, random reads deliver a lower rate of throughput. The same is true for random writing. You might find it useful to examine your workload to determine whether it accesses data randomly or sequentially. If you find disk access is predominantly random, you might want to pay particular attention to the activities being done and monitor for the emergence of a bottleneck.

• Random (direct) access, means that data can be retrieved directly from any location on the storage medium, in any order

• Sequential access, means that the data can be retrieved in the order in which it is physically stored on the medium

For workloads of either random or sequential I/O, use drives with faster rotational speeds. For workloads that are predominantly random I/O, use a drive with faster seek time.

For workloads that have high I/O rates, consider using stripe sets because they add physical disks, increasing the system's ability to handle concurrent disk requests. Notice, however, that stripe sets enabled in software can cause an increase in consumption of the processor. Hardware-enabled RAID sets eliminate this impact on the processor but increase the consumption of processing cycles on the hardware RAID adapter.

17. Solid-state hard drive

A solid-state drive (SSD) (also known as a solid-state disk [1][2][3] or electronic disk,[4] though it contains no actual "disk" of any kind) is a data storage device using integrated circuit assemblies as memory to store data persistently. SSD technology uses electronic interfaces compatible with traditional block input/output (I/O) hard disk drives.

Magnetic hard drive

A hard disk drive (HDD) is a data storage device used for storing and retrieving digital information using rapidly rotating discs (platters) coated with magnetic material. An HDD retains its data even when powered off. Data is read in a random-access manner, meaning individual blocks of data can be stored or retrieved in any order rather than just sequentially. An HDD consists of one or more rigid ("hard") rapidly rotating discs (platters) with magnetic heads arranged on a moving actuator arm to read and write data to the surfaces.