● MEMORY
Memory is a holding area for data, instructions, and information. Like MI microprocessors, memory is contained on chips connected to the system board. There are three well-known types of memory chips: random-access memory (RAM), read-only memory (ROM), and flash memory.
◆ RAM
Random-access memory (RAM) chips hold the program (sequence of presently instructions) and data that the CPU is presently processing. RAM is called temporary or volatile storage because everything in most types of RAM is lost as soon as the computer is turned off. It is also lost if there is a power failure or other disruption of the electric current going to the computer. It is permanent or non-volatile storage, such as the data stored on a hard disk. For this reason, as we mentioned earlier, it is a good idea to frequently save your work in progress to a secondary storage That is, if you are working on a document or a spreadsheet, every time minutes you should save, or store, the material.
Cache (pronounce "cash") memory improves processing by acting as temporary high-speed holding area between the memory and the CPU. The computer detects which information in RAM is most frequently used and then pies that information into the cache. When needed, the CPU can quickly access the information from the cache.
Having enough RAM is important! For example, to use the standard version Microsoft Office 2016, you need 2 GB, or 2 billion bytes, of RAM. Some applications, such as photo editing software, may require even more. Fortunately, additional RAM can be added a computer system by inserting an expansion module called a DIMM (dual in-line memory module) into the system board. The capacity or amount of RAM is expressed in bytes. There are three commonly used units of measurement to describe memory capacity.
Megabyte ( MB ) - 1 Million bytes
Gigabyte (GB) - 1 billion byte
Terabyte ( TB ) - 1 trillion bytes
Even if your computer does not have enough RAM to hold a program, it might be able to run the program using virtual memory. Most of today's operating systems support virtual memory. With virtual memory, large programs are divided into parts and the parts are stored on a secondary device, usually a hard disk. Each part is then read into RAM only when needed. In this way, computer systems are able to run very large programs.
◆ ROM
Read-only memory (ROM) chips have information stored in them by the manufacturer. Unlike RAM chips, ROM chips are not volatile and cannot be changed by the user. "Read only" means that the CPU can read, or retrieve, data and programs written on the ROM chip. However, the computer cannot write encode or change-the information or instructions in ROM.
Not long ago, ROM chips were typically used to contain almost all the instructions for basic computer operations. For example, ROM instructions are needed to start a computer, to access memory, and to handle keyboard input. Recently, however, flash memory chips have replaced ROM chips for many applications.
◆ FLASH MEMORY
Flash memory offers a combination of the features of RAM and ROM. Like RAM, it can be updated to store new information. Like ROM, it does not lose that information when power to the computer system is turned off.
Flash memory is used for a wide range of applications. For example, it is used to store the start-up instructions for a computer. This information is called the system's BIOS (basic input/output system). This information would include the specifics concerning the amount of RAM and the type of keyboard, mouse, and secondary storage device connected to the system unit. If changes are made to the computer system, these change are reflect in flash memory.
A Summary of the three types of memory.
RAM - Programs and data.
ROM - Fixed start-up instructions.
Flash - Flexible start-up instructions.
● EXPANSION SLOTS AND CARDS :
As previously mentioned, many Personal computers allow users to expand their systems by providing expansion slots on the system board. Users can insert optional devices known as expansion cards into these slots. Ports on the cards allow cables to be connected from the expansion cards to devices outside the system unit. There are a wide range of different types of expansion cards. Some of the most commonly used expansion cards are:
● Graphics cards, which provide high quality 3D graphics and animation for games and simulations. While many personal computer systems have a GPU connected directly to the system board, others connect through a graphics card. This card can contain one or more GPU chips and is standard for most gaming computers.
● Network interface cards (NIC), also known as network adapter cards, are used to connect a computer to a network. The network allows connected computers to share data, programs, and hardware. The network adapter card typically connects the system unit to a cable that connects to the network.
● Wireless network cards allow computers to be connected without cables.Wireless networks in the home are widely used to share a common Internet connection, Each device on the network is equipped with a wireless network card that communicates with the other devices.
To meet the size constraints of laptop computers, tablets, and smartphones, fingernail-size expansion cards known as SD cards have been developed. These cards plug into expansion slots located within many laptops, tablets, and smartphones.
