# Virtual Memory
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	- Additional memory without adding physical RAM
	- simulates memory using storage devices
	- Useful when RAM is inusufficient
	- Hardware and Software implementations
	- Utilizes disk drive to store memory
	- ## Why Use Virtual Memory
		- Modern operating systems require a lot of memory
		- Not enough physical RAM to multiple apps
	- ## How Virtual Memory Works
		- Memory Management Unit (MMU)
		- Unneeded data in RAM moved to hard disk
		- Swap file or page file
		- Slower that RAM, although SSDs are better than hard disks
	- ## Managing Virtual Memory in Windows
		- Performance options -> Virtual Memory
	- ## Pros and Cons of Virtual Memory
	- | Pros | Cons|
	  | Can improve system performance | Slower than physical RAM |
	  | Increases capacity for multitasking | Consumes disk space |
	  | Useful for large, memory-intensive applications | Can result in frequent hard disk access |
	  | | Leads to poor performance if incorrectly used |
- # Small Outline Dual In-line Memory Module (SODIMM)
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	- Refers to its smaller footprint
	- Performs similarly to larger DIMMs
	- ## SODIMM Versions
		- DDR
		- DDR2
		- DDR3
		- DDR4
		- DDR5
	- ## DDR5
		- Released in 2020
		- Maximum DIMM size of 128GB
		- Lower voltage at 1.1V
		- 51.2 GB/s
- # Double Data Rate 3 (DDR3) Memory
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	- Twice the speed of DDR2
	- 240-pin DIMM or 204 SODIMM
	- Incompatible with previous generations
	- ## DDR3
		- Bus clock speed between 400 and 1066 MHz
		- Cycles four times per bus cycle
		- Transfers data twice per clock cycle
		- Bandwidth between 6400 and 17066 MB/s
		- MT/s (Million transfers per second)
		- e.g., DDR3-1600 - 1600 million transfers per second
- # Double Data Rate 4 (DDR4) Memory
	- DIMM and SODIMM form factors
	- Twice the speed of DDR3
	- ## DDR4
		- 288-pin DIMM or 256-pin SODIMM
		- Incompatible with previous generations
		- Bus clock speed between 1066 and 2133 MHz
		- Bandwidth between 12800 and 25600 MB/s
		- MT/s from 1600 to 3200
- # Double Data Rate 5 (DDR5) Memory
	- Lower Power consumption
	- Twice the speed of DDR4
	- ## DDR5
		- Lower voltage at 1.1V
		- Voltage regulators
		- Additional cost
		- 51.2 GB/s
		- MT/s from 3200 to 6400
	- ## DDR5 Enhancements
		- Four times the capacity of DDR4
		- Single DIMM maximum of 128 GB
		- Die stacking
		- LRDIMM up to 4 TB
		- ![DDR Comparison.PNG](../assets/DDR_Comparison_1727099245492_0.PNG)
- # Error Checking and Correcting (ECC) Memory
	- Discover and correct single-bit memory errors
	- More reliable than non-ECC memory
	- Requires more processing power
		- ## ECC Memory
			- Data Integrity vs. processing speed
			- Sometimes it's better to slow things down
		- ## ECC Chip Comparison
			- ![ECC comparison.PNG](../assets/ECC_comparison_1727119837791_0.PNG)
		- ## ECC Error Correction
			- Uses parity
			- for every 8th bits written, 9th parity bit stored
			- For each byte, total of 1s are summed up
			- Value of parity bit compared to data
			- If parity bit matches bit count, data assumed to be correct
			- If parity bit value doesn't match, data assumed to be corrupt
			- Error correcting memory will attempt repair
			- Limited to single bit errors in a byte
			- Less common in modern systems
			- ECC memory considered reliable
			- Modern technology negates need
- # Single Channel Memory Mode
	- Data flow between CPU and RAM (memory bus)
	- 64-bit memory bus or channel
	- if one channel and two chips, channel is shared
	- ![single-channel-ram.PNG](../assets/single-channel-ram_1727121940577_0.PNG)
	-
	- ## Bus Pathways
		- Data
		- Control
		- Address
	- ## Single Channel RAM
		- Chips must share single channel
		- Memory addressed separately
- # Dual Channel Memory Mode
	- Two dedicated 64-bit buses
	- if two physical chips, each has own channel
	- if four chips, they operate in pairs
	- ![dual-channel-ram.PNG](../assets/dual-channel-ram_1727121983980_0.PNG)
	-
	- ## Two Chips
		- Channel A and B
		- Improved Performance
	- ## Four Chips
		- Four chips still benefit
		- Two chips sharing each channel
		- Still better performance
	- ## Memory Addressing
		- No conflicts
		- Simultaneous operations
		- Improved performance with multitasking
- # Triple Channel Memory Mode
	- Three separate 64-bit buses
	- if three chips, each has own channel
	- If six chips, they operate in pairs
	- ![triple-channel-ram.PNG](../assets/triple-channel-ram_1727121684610_0.PNG)
	- ## Bus width
		- 192 bits
		- Wider pathway
		- Simultaneous access
		- Dedicated chips in dedicated channels
	- ## Triple Channel Memory
		- Chips vs. slots
		- Consider leaving one channel empty when using 4 chips
- # Quad Channel Memory Mode
	- Four channels
	- Supports four memory modules in dedicated channels
	- ## Quad Channel Memory
		- All four modules required for full functionality
		- Same capacity and speed
		- When two modules installed, will operate in dual channel mode
		- When three modules installed, will operate in triple channel mode
	- ## Quad Channel RAM
		- Relies on number of installed modules
		- Depends on system specifications
		- Number of modules will determine channels
	- ## Pros and Cons of Quad Channel RAM
		- | Pros | Cons |
		  | Improved system performance | Costly|
		  |Four times memory bandwidth as single channel | |
		  | Higher capacity | |
- # Hard Drive Storage Devices
	- Electromechanical data storage
	- Rapidly rotating magnetic platter
	- Actuator arm reads and writes data
	- Data is randomly accessed
	- Non-volatile storage
	- ## Key Characteristics of HDDs
		- Mature Technology
		- Highly Reliable
		- Cost effective
		- High capacity
		- Serial ATA Interface
	- ## HDD Performance
		- Platter rotation speed (5400, 7200, 10,000, 15,000 RPM)
		- Internal cache
		- Interface Type
	- ## HDD vs. Solid-State Drive (SSD)
		- HDD underperforms SSD
		- HDD has larger capacity than SSD
	- ## 3.5 Inch HDD
		- Common in desktop systems
		- Easy to install
		- Cost-effective
		- Increased capacity
		- Available interface
	- ## 2.5 Inch HDD
		- Common in laptops
		- Can be used in desktops
		- Lower capacity
		- Slower data transfer rates
		- Less heat and noise
	- ## Hybrid Drives
		- SSD speed
		- HDD capacity
		- Cost
- # Solid-state Drive (SSD) Solutions
	- Non-volatile storage
	- No moving parts
	- Increased performance
	- ## Solid-state Drives (SSD)
		- Less prone to wear and tear associated with HDD
		- More durable over time
	- ## Improved Performance
		- Reading and writing data
		- Shorter boot times
		- Faster application launching
		- Faster file transfer
	- ## Advantages of SSDs
		- No defragmentation required
		- Quiet operation
		- More compact that HDDs
		- Lower power requirements
	- ## Disadvantages of SSDs
		- Costly
		- Lower capacity
		- Little warning of impending failure
		- Shorter lifecycle than HDD
		- Not suitable for archiving
	- ## SSD Communication Interfaces
		- Non-volatile memory express (NVMe)
		- Peripheral component interconnect express (PCIe)
		- Serial advanced technology attachment (SATA)
	- ## SSD Form Factors
		- mSATA
		- M.2
- # Redundant Drive Configurations
	- Redundant Array of independent Disks
	- Redundant and non-redundant
	- Reliable data storage
	- Low cost
	- Common in network servers
	- ## RAID Categories
		- ### Software-based RAID
			- Uses OS based software to setup and manage the RAID
		- ### Hardware-based RAID
			- Physical RAID controller card manages RAID
	- ## RAID 0 - Striping
		- ![raid0.PNG](../assets/raid0_1727124509912_0.PNG)
		- No redundancy
		- Implemented for performance
	- ## RAID 1 - Mirroring
		- ![raid1.PNG](../assets/raid1_1727124713704_0.PNG)
		- Implements redundancy
		- Implemented for redundancy
		- Only configured on 2 disks
	- ## RAID 5 - Striping with Parity
		- ![raid5.PNG](../assets/raid5_1727124888931_0.PNG)
		- At least 3 disks required up to 32
		-