AS/A2 computing 2013 July batch

[Ravichandran]

Dear students of Block 6 AS computing, welcome to the computing class. I am your facilitator Dr.Ravichandran ( you can call me Dr.Ravi), I will be your course facilitator for AS computing and A2 computing. I will start communicating with you in this discussion forum - where you can start posting your queries and useful resources.

You are highly encouraged to interact with me and also with your peers as the class begins from 30th July 2013.

All the best and keep moving. Do not hesitate to ask and send your queries if you have one.

Regards,

Dr.Ravichandran

i HAVE ATTACHED THE SYLLABUS TOO.

YOU CAN DOWNLOAD THE ATTACHMENT FILE.

[Syed Muhammad b. Syed Hood]

1.Paging is one of the memory-management schemes by which a computer can store and retrieve data from secondary storage for use in main memory.In the paging memory-management scheme, the operating system retrieves data from secondary storage in same-size blocks called pages. 

2. Memory segmentation is the division of a computer's primary memory into segments or sections. In a computer system using segmentation, a reference to a memory location includes a value that identifies a segment and an offset within that segment. Segments or sections are also used in object files of compiled programs when they are linked together into a program image and when the image is loaded into memory.

3. Fragmentation is a phenomenon in which storage space is used inefficiently, reducing capacity or performance and often both. The exact consequences of fragmentation depend on the specific system of storage allocation in use and the particular form of fragmentation.

4. Virtual memory is a memory management technique that is implemented using both hardware and software. It maps memory addresses used by a program, called virtual addresses, into physical addresses in computer memory.

5.A page table is the data structure used by a virtual memory system in a computer operating system to store the mapping between virtual addresses and physical addresses

[Maizatul Akmal Mohamad]

• paging

A technique used by virtual memory OS to help ensure that the data we need is available as quickly as possible. The operating system copies a certain number of pages from storage device to main memory. When a program needs a page that is not in main memory, the operating system copies the required page into the memory and copies another page back to the disk.

One says that the operating system pages the data. Each time a page is needed that is not currently in memory, a page fault occurs. An invalid page fault occurs when the address of the page being requested is invalid. In this case, the application is usually aborted.

• segmentation

Segmentation is a technique to break memory into logical pieces where each piece represents a group of related information. For example ,data segments or code segment for each process, data segment for operating system and so on. Segmentation can be implemented using or without using paging.

Unlike paging, segment are having varying sizes and thus eliminates internal fragmentation. External fragmentation still exists but to lesser extent.

• fragmentation

Refers to the condition of a disk in which files are divided into pieces scattered around the disk. Fragmentation occurs naturally when one use a disk frequently, creating, deleting, and modifying files. At some point, the operating system needs to store parts of a file in non-contiguous clusters. This is entirely invisible to users, but it can slow down the speed at which data is accessed because the disk drive must search through different parts of the disk to put together a single file.

Fragmentation can also refer to RAM that has small, unused holes scattered throughout it. This is calledexternal fragmentation. With modern OS that use a paging scheme, a more common type of RAM fragmentation is internal fragmentation.This occurs when memory is allocated in frames and the frame size is larger than the amount of memory requested.

• virtual memory

 An imaginary memory area supported by some OSs (for example, Windows but not DOS) in conjunction with the hardware. One can think of virtual memory as an alternate set of memory addresses. Programs use these virtual addresses rather than real addresses to store instructions and data. When the program is actually executed, the virtual addresses are converted into real memory addresses.

• page table

A page table is the data structure used by a virtual memory system in a computer OS to store the mapping between virtual addresses and physical addresses. Virtual addresses are used by the accessing process, while physical addresses are used by the hardware or more specifically to the RAM. Each mapping is also known as a page table entry (PTE)

• swapping

Swapping is a mechanism in which a process can be swapped temporarily out of main memory to a backing store, and then brought back into memory for continued execution.

Backing store is a usually a hard disk drive or any other secondary storage which fast in access and large enough to accommodate copies of all memory images for all users. It must be capable of providing direct access to these memory images.

[Ravichandran]

Spooling slides

[Maizatul Akmal Mohamad]

Date : 21/8/14 & 22/8/14

Explain parallel processing and serial processing.

Parallel processing is the simultaneous use of more than one CPU or processor to execute a program or multiple computational threads.Serial processing is the act of attending to and processing one item at a time in a sequential effort. This usually contrasted against parallel processing.

Describe 3 tasks of assembler software

An assembler software is used to convert assembly code into machine code (object code). The assembler also calculates constant expressions and resolves symbolic names for memory locations and other entities. Some assemblers may also be able to perform some simple types of instruction set-specific optimization and may even do simple rearrangement or insertion of instruction

Describe advantages of using assembly language

Assembly languages allow the use of mnemonics and names for locations in memory. Each assembly instruction mapped to a single machine instruction which meant that it was fairly easy to translate program written in assembly language. Assembly language programs can be optimized for speed ensuring that applications are able to run as fast as possible.