4.2 KiB
Virtual Memory
collapsed:: true - 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 |
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Small Outline Dual In-line Memory Module (SODIMM)
collapsed:: true- Refers to its smaller footprint
- Performs similarly to larger DIMMs
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SODIMM Versions
- DDR
- DDR2
- DDR3
- DDR4
- DDR5
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DDR5
- Released in 2020
- Maximum DIMM size of 128GB
- Lower voltage at 1.1V
- 51.2 GB/s
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Double Data Rate 3 (DDR3) Memory
collapsed:: true- Twice the speed of DDR2
- 240-pin DIMM or 204 SODIMM
- Incompatible with previous generations
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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
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Double Data Rate 4 (DDR4) Memory
- DIMM and SODIMM form factors
- Twice the speed of DDR3
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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
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Double Data Rate 5 (DDR5) Memory
- Lower Power consumption
- Twice the speed of DDR4
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DDR5
- Lower voltage at 1.1V
- Voltage regulators
- Additional cost
- 51.2 GB/s
- MT/s from 3200 to 6400
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DDR5 Enhancements
- Four times the capacity of DDR4
- Single DIMM maximum of 128 GB
- Die stacking
- LRDIMM up to 4 TB
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Error Checking and Correcting (ECC) Memory
- Discover and correct single-bit memory errors
- More reliable than non-ECC memory
- Requires more processing power
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ECC Memory
- Data Integrity vs. processing speed
- Sometimes it's better to slow things down
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ECC Chip Comparison
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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
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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
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Bus Pathways
- Data
- Control
- Address
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Single Channel RAM
- Chips must share single channel
- Memory addressed separately
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Dual Channel Memory Mode
- Two dedicated 64-bit buses
- if two physical chips, each has own channel
- if four chips, they operate in pairs
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Two Chips
- Channel A and B
- Improved Performance
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Four Chips
- Four chips still benefit
- Two chips sharing each channel
- Still better performance
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Memory Addressing
- No conflicts
- Simultaneous operations
- Improved performance with multitasking
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Triple Channel Memory Mode
- Three separate 64-bit buses
- if three chips, each has own channel
- If six chips, they operate in pairs
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Bus width
- 192 bits
- Wider pathway
