Solutions To Programmable Array Logic Problems Through Network Support

Programmable Logic Array (PAL) is one of the earliest field programmable logic devices, launched in the market in 1978 by Monolithic Memories Inc. It comprises a programmable read only memory core and output circuitry,employed to implement particular digital logic functions. PAL devices are field programmable, which means the device could be programmed by the user. However programming a PAL needs expertise. In case the user faces any problem in PAL programming, an experienced PC support provider should be consulted.

Brief History
In the early days, small scale integration components like transistor transistor logic (TTL) were used to build a digital circuit. Among the TTL families, 7400 series was very popular. It consisted of variety of logic gates, multiplexers,demultiplexers,flip flops,etc. After the advent of PAL, SSI devices became obsolete.

PAL Technology
Early versions of PAL were 20 pin dual inline package. Bipolar transistor technology was used to fabricate PAL. Titanium tungsten programming fuses were used in those one time programmable devices. Later on,Advanced Micro Devices employed CMOS technology to manufacture PALs for which it provided extensive network support.

Architecture Of PAL
The programmable elements in a PAL link the true and complemented inputs to the AND gates. These AND gates are also called Product Terms. Product Terms are ORed altogether to constitute a sum of products logic array. The PAL architecture comprises two principal components, namely Programmable Logic Plane and Output Logic Cells.

Programmable Logic Plane
Programmable Logic Plane is nothing but a programmable read only memory which routes the signals at the input pins to the output logic macro cells. PAL devices feature transistor cell arrays which are organized in a fixed OR programmable AND fashion. Sum of products logic equations for each output in terms inputs and feedback from output are implemented by these arrays.

Output Logic Macro Cells
A standard 20 pin PAL features 8 outputs,10 inputs, 1 pin for power and 1 pin for ground. In the active state the signal at the output pins is 0 volt. The output could be either combinational or registered. A standard PAL device features different output structures, known as Output Logic Macro Cells or OLMC. Earlier versions of PAL, such as 16L8 and 16R8 had fixed OLMCs at the time of manufacturing. Later, in 1983, AMD launched 22V8, whose OLMCs could be configured by the user as registered or combinational.

PAL Programming
PAL programs are written using Hardware Description Languages, such as ABEL,CUPL and PALSM. These are computer aided design programs, which convert the PAL logic equations written in a text file to binary files, like JDEC and HEX files. These binary files are programmed into PAL devices using special programming devices. The manufacturers as well as the third party manufacturers render strong PC support for PAL programming issues.

PALASM Language
PALSM language was invented to write boolean logic equations for the configured output pins using the configured input pins. The equations are written in a text file,which is then converted into a binary file using compiler. Monolithic Memories Incorporation (MMI) wrote first compiler for PALASM language in FORTRAN IV on IBM 370/168. MMI supplied the free compiler and network support to the PALASM users.

ABEL Language
Advanced Boolean Expression Language (ABEL) is a hardware description language developed by Data I/O Corporation in 1983 for programming PALs. It employs concurrent equations,truth table logic format and sequential state machine diagram. Data I/O Corporation provides compiler as well as PC support for ABEL language.

CUPL Language
CUPL language was invented by Logical Devices Incorporation. Its earlier versions ran under MS DOS. Now it comes as an integrated development package of windows. CUPL programming issues could be resolved with the network support of Logic Devices Inc.

PC Support For PAL Programming
PAL programing requires experience in handling compiler as well as PAL programming devices which could be made easier with the help of network support providers. PAL manufacturers provide extensive PC support for PAL programming. Apart from that, a lot of third party vendors render strong network support for PAL programming issues.

Daniel Hughes is one of most heralded content writer of PCCareNCure.com. Pccarencure offers 24x7 PC Support to millions of customers.

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How Block Storage Array Works

The PS array is block storage array that only knows about areas of a volume that have ever been written. The PS Series GUI reports this information for each volume. Volume allocation grows automatically due to application data writes. If later the application frees up space, the space is not marked as unused in the PS Series GUI. Hence the difference in views between the OS file system and the PS Series GUI.

With thin provisioned volumes, this perception can be more pronounced. Thin provisioning is a storage virtualization and provisioning model that allows administrators to logically allocate large addressable storage space to a volume, yet not physically commit storage resources to this space until it is used by an application. For example, using thin provisioning you can create a volume that an application views as 3 TB, while only allocating 300 GB of physical storage to it. As the operating system writes to the volume, physical disk space is allocated to the volume by the storage array. This physical disk space is taken from the available free space in the pool automatically and transparently. As a result, less physical storage is needed over time, and the standard storage problem is eliminated. The administrator enjoys management benefits similar to over-provisioning, yet maintains the operational efficiencies of improved physical storage utilization. This more efficient use of physical storage resources typically allows an organization to defer or reduce storage purchases.

So Thin provisioning is a forward planning tool for storage allocation in which all the storage an application will need is allocated upfront, eliminating the trauma of expanding available storage in systems that do not support online expansion. Because the administrator initially provisions the application with all the storage it need, repeated data growth operations are avoided.

A thin-provisioned volume also grows automatically as the application data writes. The space is drawn from the pool free space (rather than having been pre-allocated in a normal volume). If later the application frees up space, the space is free in the file system but is not returned to the free space in the PS Series pool. The only way to reduce the physical allocation in the SAN is to create a new volume, copy the application data from the old volume to the new, and then delete the old volume.

A similar problem is when the initiator OS reports significantly more space in use than the array does. This can be pronounced in systems like VMWare that create large, sparse files. In VMWare, if you create yourself a 10GB disk for a VM as a VMDK file, VMWare does not write 10GB of zeros to the file. It creates an empty (sparse) 10GB file, and subtracts 10GB from free space. The act of creating the empty file only touches a few MB of actual sectors on the disk. So VMWare says 10GB missing but the array says only 2MB written to it.

In some cases the amount of space used on the array will show less than what is shown by the OS. When ESX 3.x creates a 20GB VMDK, it doesn't actually write 20GB of data to the volume. A small file is created, then ESX tells the file allocation table that 20GB has been allocated. Over time as data is actually written and deleted, then ESX says there is less space allocated than what the array GUI indicates.

Eddison Sherry had been working in Linux and Unix flavours for long years. He had been writing blogs and article on the Linux Storage , Linux Commands and Linux Server Administration. If you are working on Linux or Unix Server its best to have a look on his blogs at http://www.expertslogin.com/

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