Storage Area Networks are typically used to provide access to data storage. These make sure that storage devices such as disks, tape drives etc. can be accessed by an operating system as system storage devices.Storage Area Networks are quite cheap and so are used both by large conglomerates and small businesses.An image that illustrates storage area networks is as follows −Components of Storage Area NetworksThe different components in storage area networks are −Host LayerAll the servers that provide access to the storage area network collectively constitute the host layer. These servers have host bus adapters that allow the operating system ... Read More

The hot standby mode is a fail-safe in which a hot standby component is part of an active system. If any component of the system fails, the hot standby component takes its place. In general, a hot standby can refer to any device, system etc. that overtakes operation from a failed device and reduces the startup delay that would otherwise be huge.A figure to further explain the hot standby mode is as follows −In general, it is expected that a system will have some failures. So, a hot standby is necessary to combat these failures.At the extreme, a hot standby ... Read More

Cache is a type of memory that is used to increase the speed of data access. Normally, the data required for any process resides in the main memory. However, it is transferred to the cache memory temporarily if it is used frequently enough. The process of storing and accessing data from a cache is known as caching.Uncached System vs Cached SystemA figure to better understand the difference between cached and uncached system is as follows −Some important points to explain the above figureare −In an uncached system, there is no cache memory. So, all the data required by the processor ... Read More

Asymmetric multiprocessor systems are a part of multiprocessor systems along with symmetric multiprocessor systems. Multiprocessor systems have multiple processors working in parallel that share the computer clock, memory, bus, peripheral devices etc.Features of Asymmetric MultiprocessingSome of the key points about asymmetric multiprocessing are explained with the help of the following diagram −Here are the points −All the processors are not treated equally in asymmetric multiprogramming. For example, a processor may handle only I/O related operations and another may handle only operating system code. This is in direct contrast to symmetric multiprocessing systems because there all processors are treated equally and ... Read More

Low earth orbit (LEO) satellites systems orbit below 2000 km from the earth’s surface, i.e. below the lower Van Allen belt. They move at very high speeds and may not have any fixed space with respect to the earth.The following diagram depicts LEO satellites in their orbits.Features of LEO SatellitesA network of LEO satellites are needed for global coverage as their orbits are not geostationary.These satellites are not as powerful as the MEO and GEO satellites.Due to their high speeds, satellites move in and out of the earth station’s range from time to time. So, data is handed off from ... Read More

Most computer systems are single processor systems but multiprocessor systems are increasing in importance nowadays. These systems have multiple processors working in parallel that share the computer clock, memory, bus, peripheral devices etc.There are mainly two types of multiprocessor systems. These are −Symmetric Multiprocessor SystemAsymmetric Multiprocessor SystemIn symmetric multiprocessing, multiple processors share a common memory and operating system. All of these processors work in tandem to execute processes. The operating system treats all the processors equally, and no processor is reserved for special purposes.Features of Symmetric Multiprocessing (SMP)Some of the key points about symmetric multiprocessing are explained with the help ... Read More

VSATs (Very Small Aperture Terminals) is a two way, lost cost, ground micro station for transmitting data to and from communication satellites. A VSAT has a dish antenna with diameters between 75 cm to 1 m, which is very small in comparison with 10 m diameter of a standard GEO antenna. It accesses satellites in geosynchronous orbits or geostationary orbits. Data rates in VSATs ranges from 4 Kbps to 16 Mbps.Configurations of VSATsStar Topology − This has a central uplink site which transmits data from and to each VSAT through the satellite.Mesh Topology − Each VSAT transmits data via the ... Read More

Geosynchronous Satellite and Geosynchronous Orbit (GSO)A geosynchronous satellite is a communication satellite that has an orbital period same as the period of rotation of the earth. Hence, it appears to be permanently in the same area of the sky at a particular time each day when viewed by an observer on the earth.The orbit in which a geosynchronous satellite is placed is called geosynchronous orbit (GSO). Its orbital period is the sidereal day, i.e. 23 hours 56 minutes 4 seconds and its orbital altitude is 35, 800 km.Geostationary Satellite and Geostationary Orbit (GEO)A circular geosynchronous satellite which is placed at ... Read More

Cache is a type of memory that is used to increase the speed of data access. Normally, the data required for any process resides in the main memory. However, it is transferred to the cache memory temporarily if it is used frequently enough.A diagram to better understand the data transfer in cache management is as follows −Cache PerformanceThe cache performance can be explained using the following steps −If a process needs some data, it first searches in the cache memory. If the data is available in the cache, this is termed as a cache hit and the data is accessed ... Read More

Memory management plays an important part in operating system. It deals with memory and the moving of processes from disk to primary memory for execution and back again. Some basic concepts related to memory management are as follows −Virtual Address Space and Physical Address SpaceThe address generated by the CPU is known as the virtual address and the address seen by the memory is known as the physical address. In compile time and load time address binding schemes, both the virtual and physical address are the same. They differ only in the execution time address binding scheme.All the logical addresses ... Read More