Random Access Memory

Published Date: 02 Nov 2017

RAM is playing a very big role in temporary storing and retrieving data in a very short duration. Besides that, it must be paired with the CPU (Central Processing Unit) and also a storage drive such as hard disk, flash drive and etc. in order the RAM to work perfectly.

Random Access Memory (RAM) perform as a high speed temporary storage intercept point, between the permanent storage drive and the CPU unit in order to transfer data from the storage drive to the CPU unit without taking a long time. So with the help of RAM, it could saves up time and has a better system efficiency.

C2: How RAM works

RAM is a hardware that enables the computer to temporary store data into this device, so it can be retrieve back in a shorter time rather than getting it from the hard disk that takes longer time. In order this to work, a transistor and a capacitor are needed in order to create a memory cell to temporary store the data. Each memory cell is represented by a single bit. The bit is calculated by a "0" and a "1". The combination of "0" and "1" can generate out a series of unique number to represent the data.

In order for the PC to get information, the CPU (Central Processing Unit) sends a request to memory controller, and a report will be generated and sends back to the CPU when the data that the CPU requesting is ready to deliver. The duration of sending and receiving the report is very dependent on the speed of the RAM and also other factors such as the bus speed. When the data is ready to deliver, the system clock will sends a signal to all the hardware that is represented by "megahertz" (MHz). The higher amount of clocks can be sending out, the faster and higher amount of task can be done. But still, it still need to depending on what architecture that is using to pair with the RAM.

C3: Types of RAM

There are 3 types of common RAM (Random Access Memory) being used for computer. The 3 types of RAM are SDRAM (Synchronous DRAM), DDR(Double Data Rate SDRAM) and lastly, the Rambus DRAM (RDRAM).

No doubt that the old SDRAM (Synchronous DRAM) would bottleneck our system if we implement it into our common computer system nowadays. SDRAM is running with 3.3 volt and it also built with 168 pins for each RAM chip. The first SDRAM was set to run at a 66MHz. After sometime, the SDRAM was able to run at a 133MHz speed.

The most common type of RAM that we are using nowadays for our computer system is the DDR (Double Data Rate SDRAM). For this DDR, they are 3 level of RAM which is DDR, DDR2 and DDR3. DDR RAM is a upgraded version of the first generation of SDRAM. It enables to run at the two times faster than the normal SDRAM. The first DDR RAM was running at 333MHz, and when comes to DDR2, it was upgraded to 667MHz and 800MHz, and the latest DDR3 is able to set to run at as high as 1600MHz and also it able to have a better performance while the first DDR was set to run at 2.5 volt. The new DDR2 RAM is only consuming 1.8 volt and finally the latest DDR3 RAM is set to run at a 1.5 volt, which is 30% lesser than the previous DDR2 RAM. Besides that, it also have slightly higher amount of pins for the RAM. Unfortunately, this DDR is incompatible with old SDRAM slot. But it is implemented to run under a similar of bus slot, so that it's easy to implement into the bus slot than the RDRAM.

The Rambus DRAM is the only choice for the Intel's Pentium 4 architecture. This Rambus DRAM comes with 3 choices that are PC600, PC700 and PC800. Despite the PC800 Rambus DRAM have the double the maximum performance as the old PC100 SDRAM, but it has a higher amount of latency. This type of RAM is engineered with multiple channels motherboard. It could be the best memory output when it is running with a PC1066 Rambus DRAM memory.

D1: Why a memory hierarchy is required

A memory hierarchy is required is because to reduce the time taken for the user to retrieve the data that are being used frequently. With this technology, the user can retrieve data from the disk without taking a long time.

D2: How a memory hierarchy works

A memory hierarchy contains certain level of memory in a computer which is from fastest to slowest in term of speed. The fastest memory would be CPU registers, follow by L1 cache, L2 cache, main memory, virtual memory and the slowest would be the disk. A processor that sends and receives data from the RAM on each CPU cycle could be just only operating around ten percent or even less of its maximum speed. Thus, this situation could be slowing down the entire system just because it must retrieve the data from the disk frequently.

The memory hierarchy works like a stage that performs the most priority to the lease priority. First the CPU will perform a search in the TLB (Translation Lookaside Buffer). If the data is available, it will generate a PA and it will search through the Cache and return the data value to the CPU. If during the TLB process unable to retrieve the data, it will perform a deeper search that include a page table and sends back the data to the cache for verifying purpose and back to the CPU again. If still unable to obtain the data that is requesting, it will get page from the secondary memory and update the main memory, cache and page table entry, and back to CPU and perform a new search again.

References

Memory hierarchy: http://www.yourdictionary.com/computer/memory-hierarchy; http://bugclub.org/eric/memory/hierarchy.html; http://www.computermemoryupgrade.net/types-of-computer-memory-common-uses.html; http://www.howstuffworks.com/ram.html; http://www.buycomputermemory.com/system-ram.html.

Pictures: http://tekgems.com/images/large/RAM-512DDR2700-N-unit.jpg; http://www.build-gaming-computer-guide.com/image-files/ddr3-vs-ddr2-ram.jpg; http://www.techimo.com/forum/attachments/imo-community/19192d1202595600-counting-1000-images-256mb_sdram.jpg; http://student.psru.ac.th/~493244039/images/rram.gif.