Top 10 List of Week 05

1. Memory vs Storage
   Your computer’s main memory is called RAM. You can think of it as a workspace the computer uses to get work done. When you double-click on an app, or open a document, or, well, do much of anything, RAM gets used to store that data while the computer is working on it. There’s also storage: a hard disk drive or solid state drive where data is recorded and can stay indefinitely, to be recalled as necessary. That might be a tax return, a poem in a word processor, or an email. By comparison, RAM is volatile — the information that’s put in there disappears when the power is turned off or when the computer is reset. Stuff written to disk stays there permanently until it’s erased, or until the storage medium fails.

2. Difference between DDR4 and DDR3
   Both DDR3 and DDR4 are the versions of Double Data Rate (DDR). The clock speed of DDR3 vary from 800 MHz to 2133 MHz, where 2133 MHz is the its peak in some cases, generally clock speed is vary between 1600 to 1800 MHz. The minimum clock speed of DDR4 is 2133 MHz and it has no defined maximum clock speed.

3. How Computer Memory Works
   In many ways, our memories make us who we are, helping us remember our past, learn and retain skills, and plan for the future. And for the computers that often act as extensions of ourselves, memory plays much the same role. In this video, Kanawat Senanan explains how computer memory works.

4. What Is a Cache? A Complete Guide to Caches and Their Uses
   We all learned cache in Introduction to Computer Organization course in past semester. A cache is a special storage space for temporary files that makes a device, browser, or app run faster and more efficiently. A cache is a reserved storage location that collects temporary data to help websites, browsers, and apps load faster. Whether it’s a computer, laptop or phone, web browser or app, you’ll find some variety of a cache.

5. What is Memory Swapping?
   Memory swapping is a computer technology that enables an operating system to provide more memory to a running application or process than is available in physical random access memory (RAM). When the physical system memory is exhausted, the operating system can opt to make use of memory swapping techniques to get additional memory.

6. Types of Cache Misses
   Cache Miss occurs when data is not available in the Cache Memory. When the CPU detects a miss, it processes the miss by fetching requested data from main memory. There are various types of cache misses such as: Compulsory Miss, Capacity Miss, Conflict Miss, and Coherence Miss. This article explains all of them very clearly.

7. Dynamic Memory Allocation in C
   C Dynamic Memory Allocation can be defined as a procedure in which the size of a data structure (like Array) is changed during the runtime. “malloc” or “memory allocation” method in C is used to dynamically allocate a single large block of memory with the specified size. It returns a pointer of type void which can be cast into a pointer of any form. “calloc” or “contiguous allocation” method in C is used to dynamically allocate the specified number of blocks of memory of the specified type. “realloc” or “re-allocation” method in C is used to dynamically change the memory allocation of a previously allocated memory.

8. Memory Hierarchy in Computer Architecture
   The memory in a computer can be divided into five hierarchies based on the speed as well as use. The processor can move from one level to another based on its requirements. The five hierarchies in the memory are registers, cache, main memory, magnetic discs, and magnetic tapes. The first three hierarchies are volatile memories which mean when there is no power, and then automatically they lose their stored data. Whereas the last two hierarchies are not volatile which means they store the data permanently.

9. Virtual Memory Definition
   Virtual memory is the use of space on a hard disk drive (HDD) to simulate additional main memory. Virtual memory permits software to run in a memory space (i.e., a logical memory) whose size is greater than the computer’s RAM. Most personal computers sold today contain from 256MB to 1024MB of RAM. While this is huge in comparison to what was common just a few years ago, it is still often insufficient to simultaneously run all of the programs that users attempt to run. The reason is that the size of many programs has continued to increase accompanying the growth in memory sizes and HDD capacities, largely in order to add more features (including fancier graphics).

10. Copy on Write
    Copy on Write or simply COW is a resource management technique. One of its main use is in the implementation of the fork system call in which it shares the virtual memory(pages) of the OS. In UNIX like OS, fork() system call creates a duplicate process of the parent process which is called as the child process.