Difference Between Memory Types ,Importance Of A Hardware Compatibility List

Hot swapping/ hot spare: A hot spare is a spare unit that is ready to take on the job of the main unit in the even of failure. Hot spare refers to the physical unit such as a disk drive or even a standby computer, such as in a clustered configuration. The failure may or may not be noticed by clients. For example, if the RAID system is configured with RAID 0, a failure may be noticed by the clients, whereas, if configured with RAID 5, the failure may not be noticed (in case of single point failure). Hot-Swapping is the ability to add and remove devices to a computer while the computer is running and have the operating system automatically recognize the change. Hot plugging is also called hot swapping

Memory Types RAM stands for Random Access Memory. There are basically two types of RAM:

1. DRAM - Dynamic RAM, and

2. SRAM - Static RAM. SRAM, being very expensive, commonly used for Cache memory. DRAM, being cheaper, is used for main memory.

DDR (Double Data Rate)

DDR SDRAM/ DDR/ DDR1: It transfers data on both rising and falling edges of the clock signal. It operates at 2.5 volts. DRR RAM runs at twice the processor speed. It uses prefetch buffer which is a memory cache on RAM module that stors sata before it is actuly needed. This buffer size is 2 bits. Connector size is 184 pins.
DDR2: It is an enhancement of DDR SDRAM with prefetch buffer of size 4 bits. It also has enhanced registers and on-die termination. It also works at higher bus speed. It operates at 1.8 volts. Pin size is 240 pins.
DDR3: It is an enhancement of DDR2 with prefetch buffer size 8 bits. Data rate is twice that of DDR2. It operates at 1.5 volts. Pin size is 240 pins.

Fully Buffered DIMM

It is a memory technology which can be used to increase reliability and density of memory systems. Conventionally, data lines from the memory controller have to be connected to data lines in every DRAM module, i.e. via multidrop buses. As memory width, as well as access speed, increases, the signal degrades at the interface of the bus and the device.

Memory compatibility

		Industry Name	Clock Speed (MHz)	Data Transfer/second(million)	CAS Latency	Prefetch bit	Supply voltage	Pins
DDR SDRAM	DDR-200	PC-1600	100	200	2,2.5, 3 clock	2 bit	2.5 V	184
	DDR-266	PC-2100	133	266
	DDR-333	PC-2700	166	333
	DDR-400	PC-3200	200	400
	DDR-500	PC-4000	250	500
DDR2	DDR2-400	PC2-3200	100	400	3,4,5 clock	4 bit	1.8 V	240
	DDR2-533	PPC2-4200	133	533
	DDR2-667	PC2-5300	166	667
	DDR2-800	PC2-6400	200	800
	DDR2-1066	PC2-8500	266	1066
DDR3	DDR3-800	PC3-6400	100	800	5,6,7,8,9,10 clock	8 bit	1.5 V	240
	DDR3-1066	PC3-8500	133	1066
	DDR3-1333	PC3-10600	166	1333
	DDR3-1600	PC3-12800	200	1600

1.4 Explain the importance of a Hardware Compatibility List (HCL)

RAM manufactures and reseller provide a Hardware Compatibility List (HCL). Server administrators should look this HCL to find about a specified system board and processor.

Virtualization is the use of software to allow a piece of hardware to run multiple operating system images at the same time. The simulated machines are called virtual machines. Recently, CPUs are equipped with virtualization features. Intel VT and AMD's AMD-V are two examples of CPU virtualization. HCL will show if the hardware you are going to use is supported by the operating system on the server.