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Types of main memory;
The memory unit can be implemented using a variety of memory chips- different speeds, different manufacturing technology, and different sizes. The main memory types are:
1- Read Only Memories (ROM):
ROMs allow only read operation to be performed. This memory is non-volatile. Most ROMs are programmed and cannot be altered. This type of ROM is cheaper to manufacture than other types of ROM. The program that controls the standard I/O functions (called BIOS) and configuration software are kept in ROM,.
Other types of ROM include:
A- Programmable ROM (PROM).
B- Erasable PROM (EPROM) is read only memory that can be reprogrammed using special equipment.
C- EAPROM, Electrically Alterable Programmable ROM is a Read Only Memory that is electrically reprogrammable.
2- Read/Write Memory (RAM):-
Read/Write memory is commonly referred to as Random Access Memory (RAM), it is divided into static and dynamic.
A-Static RAM (SRAM): used for implementing CPU registers and used for special high speed memory called cache memory this greatly improves system performance. Static RAM keeps its value without having to be refreshed.
B-Dynamic RAM (DRAM), the bulk of main memory in a typical computer system consists of dynamic Ram. DRAM is where programmed, data are kept when a program is running. It must be refreshed with in less than a millisecond or losses its contents.
The differences between RAM AND ROM
NOTE: The Main Memory is called also primary memory or
primary storage
RAM ROM
1 - Stand foe Random - Access memory 1 - stand for Read Only Memory
2 - Read /Write memory 2 - READ Only Memory
3 - Sending data (writing) to RAM memory address is called destructive write because the new data erases whatever was there before
3 - Sending data to ROM memory address is in effective because the contents of ROM can not changed (write not allowed ) because this memory for read only
4 - form of primary storage(main memory) for holding temporary data and instruction
4 - form of primary storage(main memory) for holding permanent data and instruction
5 - Volatile : program and data are erased when the power is off
5 - Permanent : program and data are intact even power is off 6 - Type of RAM is a- Static RAM b- Dynamic RAM
6 - Type of ROM is a- PROM b-EPROM c- EAPROM
Motherboard (System Board)
. It contains the processor, main memory, connectors, and expansion slots for optional cards. The slots and connectors provide access to such components as ROM, RAM, hard disk, CD-ROM drive, additional memory, video unit, keyboard, mouse, parallel and serial device, sound adapter and cache memory. A bus with wires attached to the system board connects the components. It transfers data between the processor, memory and external devices.
Bios:: Short for (Basic Input / Output System), Bios is a chip located on all
computer motherboard that contains instructions and setup for how your system should boot and how it operates. To the right is a picture of what a BIOS chip may look like in your computer. The BIOS includes instructions on how load basic computer hardware and includes a test referred to as a POST (Power On Self Test) that helps verify the computer meets requirements to boot up properly, if the computer does not pass the POST, you will receive a combination of beeps indicating what is malfunctioning within the computer.
In most PCs, the BIOS have four main functions:-
1-POST: - Test computer hardware, ensuring hardware is properly functioning before
starting process of loading operation system. Additional information on the POST can be found on our POST/Beep Code Page.
2- Bootstrap Loader:- Process of location the operating system. If capable operation
system located, BIOS will pass the control to it.
3-BIOS:-Software/Drives that interface between the operating system and your
hardware. When running DOS or Windows you are using complete BIOS support.
4-BIOS/CMOS Setup:- Configuration program that allows you to configure
hardware setting including system setting such as computer password, time, and data.
