Spooling & Buffering | Operating System - Computer Science Engineering (CSE) PDF Download

What exactly Spooling is all about?

SPOOL is an acronym for simultaneous peripheral operations on-line.  It is a kind of buffering mechanism or a process in which data is temporarily held to be used and executed by a device, program or the system. Data is sent to and stored in memory or other volatile storage until the program or computer requests it for execution.
In a computer system peripheral equipments, such as printers and punch card readers etc (batch processing), are very slow relative to the performance of the rest of the system. Getting input and output from the system was quickly seen to be a bottleneck. Here comes the need for spool.
Spooling works like a typical request queue where data, instructions and processes from multiple sources are accumulated for execution later on. Generally, it is maintained on computer’s physical memory, buffers or the I/O device-specific interrupts. The spool is processed in FIFO manner i.e. whatever first instruction is there in the queue will be popped and executed.

Applications/Implementations of Spool

1. The most common can be found in I/O devices like keyboard printers and mouse. For example, In printer, the documents/files that are sent to the printer are first stored in the memory or the printer spooler. Once the printer is ready, it fetches the data from the spool and prints it.
   Even experienced a situation when suddenly for some seconds your mouse or keyboard stops working? Meanwhile, we usually click again and again here and there on the screen to check if its working or not. When it actually starts working, what and wherever we pressed during its hang state gets executed very fast because all the instructions got stored in the respective device’s spool.
2. A batch processing system uses spooling to maintain a queue of ready-to-run jobs which can be started as soon as the system has the resources to process them.
3. Spooling is capable of overlapping I/O operation for one job with processor operations for another job. i.e. multiple processes can write documents to a print queue without waiting and resume with their work.
4. E-mail: an email is delivered by a MTA (Mail Transfer Agent) to a temporary storage area where it waits to be picked up by the MA (Mail User Agent)
5. Can also be used for generating Banner pages (these are the pages used in computerized printing in order to separate documents from each other and to identify e.g. the originator of the print request by username, an account number or a bin for pickup. Such pages are used in office environments where many people share the small number of available resources).

Difference between Spooling and Buffering

There are two ways by which Input/output subsystems can improve the performance and efficiency of the computer by using a memory space in the main memory or on the disk and these two are spooling and buffering.
Spooling: Spooling stands for Simultaneous peripheral operation online. A spool is similar to buffer as it holds the jobs for a device until the device is ready to accept the job. It considers disk as a huge buffer that can store as many jobs for the device till the output devices are ready to accept them.
Buffering: The main memory has an area called buffer that is used to store or hold the data temporarily that is being transmitted either between two devices or between a device or an application. Buffering is an act of storing data temporarily in the buffer. It helps in matching the speed of the data stream between the sender and the receiver. If the speed of the sender’s transmission is slower than the receiver, then a buffer is created in the main memory of the receiver, and it accumulates the bytes received from the sender and vice versa.
The basic difference between Spooling and Buffering is that Spooling overlaps the input/output of one job with the execution of another job while the buffering overlaps the input/output of one job with the execution of the same job.

Differences between Spooling and Buffering:

• The key difference between spooling and buffering is that Spooling can handle the input/output of one job along with the computation of another job at the same time while buffering handles input/output of one job along with its computation.
• Spooling stands for Simultaneous Peripheral Operation online. Whereas buffering is not an acronym.
• Spooling is more efficient than buffering, as spooling can overlap processing two jobs at a time.
• Buffering uses limited area in main memory while Spooling uses the disk as a huge buffer.

Comparison chart: