Understanding RAM Memory Types and Functionality
Understanding RAM Memory: Types and Functionality
Generalities: Physically, RAM is formed by a series-connected integrated circuit chip, a data bus, and an address bus. There are different types of RAM:
- ROM (Read-Only Memory): Contains information that cannot be changed, and this information is not cleared at shutdown.
- RAM (Random Access Memory): The information can be read and modified many times. The information is erased when the RAM is powered off.
Applications are loaded into RAM when the user executes them, and the values used by these programs are stored as variables in RAM.
DRAM vs. SRAM
DRAM (Dynamic RAM):
- Cheaper and allows for a greater quantity of information to be stored in the same space as SRAM.
- Bits are stored as electrical charges on tiny capacitors.
- Capacitors discharge naturally, so they need to be periodically recharged by a refresh process.
SRAM (Static RAM):
- Faster and more expensive than DRAM.
- More complex constitution.
Two channels are needed for communication between the MP (Microprocessor) and memory: the data bus and the address bus.
How DRAM Works
Memory Read: The MP puts a voltage on each of the address lines, indicating a specific memory position to access.
Memory Write: The MP places a voltage on each of the address lines, indicating a memory position to access. The MP also places the data to be written on the data bus.
A grouping of 8 bits is called a byte. Each byte represents an instruction, part of a program, a hexadecimal numeric value, or an alphanumeric character belonging to the ASCII character set. 1024 bytes = 1 Kbyte. Memory circuits are implemented in integrated systems. The mounting of these chips is standardized by using printed circuit wafers with several of these integrated circuits and contacts with a base mounting plate.
Types of RAM and Basic Characteristics
Memory Cycle Time: The time elapsed since the MP issues a read order to the time the value is available from the memory position. Memory chips must operate at a speed as close as possible to the MP, although they are never as fast. To solve this problem, various methods were devised, the most used being cache memory.
MPs with 64-bit bus: Pentium II, P4, Athlon, Duron, and Sempron use 168-pin DIMMs (DDR, DDR2, and DDR3 240).
Error Detection and Correction
To increase security in memory, two basic methods are used:
- Adding a parity bit for a certain number of data bits.
- ECC (Error Checking and Correction): Checks and corrects a single bit automatically, without stopping the system. The computer stops when more than 2 erroneous bits are detected. This system is much more reliable than the parity bit method but requires more memory chips.
Types of RAM by Constitution
SDRAM (Synchronous DRAM): A redesigned chip that optimizes sequential data transfer. This memory provides all requested data by showing only the starting address of the burst. This technique eliminates delays associated with decoding addresses. Supports bus speeds of up to 100MHz. Presented in 168-pin DIMMs.
DDR (Double Data Rate): Carries out 2 transfers per clock cycle.
DDR2: Makes 4 transfers per clock cycle. The DIMM has 240 contacts and is powered by 1.8V.
DDR3: Powered by 1.5V, has 240 contacts, is faster, and consumes less power than DDR2.
Placement of DRAM Modules
Read the documentation that comes with the motherboard to find out the type and capacity of memory modules it supports. The memory banks are marked on the base plate. The orientation is marked. If not, however, a module can only fit in one position. Place the module on the slot and push down on the side tabs to snap it into position with care and without forcing it.
Troubleshooting
There are three main reasons for memory problems: the memory is damaged, it is installed incorrectly, or the motherboard socket is damaged.
Computer Does Not Start After Installing Memory: Verify that it is correctly installed and that we have made the correct amplification. If this does not solve the problem, the memory is defective or not supported by the motherboard.
Continuous Errors and Crashes: Such failures can be due to many causes. Check with a diagnostic program. If the RAM memory fails, the normal procedure is to try the modules on another computer and other modules on that machine.