3.2 Given a scenario, Install the appropriate RAM Flashcards
What happens when a process is executed?
Image is loaded from disk into memory
Instructions are fetched from system memory & into the CPU’s cache & registers as required. This process is handled by the memory controller
How is system memory implemented as?
RAM
Meaning of RAM?
Random Access Memory
What is RAM faster than?
Hard drives
What does it mean that RAM is volatile?
Only stores data when powered on
What does the amount of system RAM determine?
PC’s multitasking & handling of large files
What does pagefile or swap space refer to?
Portion of a hard drive reserved for virtual memory
What does virtual RAM refer to?
Using storage to supplement physical RAM
With virtual RAM, what does the OS do?
Assigns memory to processes in 4KB pages
Why does the OS use a page-based systen in Virtual RAM?
To move inactive pages to swap space to free up RAM
Swap space is a portion of a storage drive used as virtual memory when the physical RAM is full. It temporarily holds inactive memory pages, freeing up RAM for active processes.
Why does paging slow down the computer?
This is related to virtual RAM
Disk transfer rates are slower than RAM transfer rates
Another purpose of virtual RAM besides supplementing physical RAM with storage?
To protect the operation & integrity of a PC
How can virtual RAM protect a PC?
Allowing the OS to manage shared virtual memory for multiple processes
Virtual memory abstraction enhances system security and stability by centrally managing memory allocation, preventing process interference, and enforcing security measures, surpassing the reliability of direct access to physical RAM for each process.
What type of memory is mainly used in modern computer systems?
DDR SDRAM (aka RAM)
Meaning of DDR SDRAM?
Double Data Rate Synchronouse Dynamic Random Access Memory
3 types of memory used in computer systems?
- DRAM
- SDRAM
- DDR SDRAM
How does Dyanmic RAM (DRAM) store data?
As electrical charges in bit cells, each compromising a capacitor
A transistor reads whether the capacitor hold a charge, representing 1, or not, representing 0
Why is Synchronous DRAM (SDRAM) so-called that way?
Its speed is synchronized to the motherboard system clock
How does DDR SDRAM add on to SDRAM?
Makes 2 data transfers per clock cycle
This effectively double the data transfer rate compares to traditional SDRAM
How are DDR memory modules labeled?
Using the max theoretical bandwidth
i.e. PC1600, PC2100, etc.
In this memory example - DDR-200 PC-1600 - What does DDR-200 mean?
Data rate of 200 MT/s
MT/s = Megatransfers per second
The DDR-200 designation signifies a 100MHz internal memory clock speed. With DDR, the effective data rate doubles the clock speed, resulting in 200 MT/s
In this memory example - DDR-200 PC-1600 - What does PC-1600 mean?
Peak transfer rate of 1600 MBps (1.6 GBps)
PC-1600” signifies the memory’s peak transfer rate, calculated by multiplying the data rate (200 MT/s) by the bytes transferred per operation. With DDR memory doubling the transfer rate by operating on both edges of the clock signal, and each transfer carrying 8 bytes (64 bits), the peak rate reaches 1600 MBps (1.6 GBps).
How do subsequent generations of DDR technology increase bandwidth?
“subsequent generations of DDR technology” refers to DDR2, DDR3, DDR4, & DDR5
By multiplying the bus speed
This produces scalable speed improvements without making the memory modules too unreliable or hot. Design improvements also increase the max possible capacity of each memory
Data rate of DDR3 RAM?
Up to 2133 MT/s
Transfer rate of DDR3 RAM?
Up to 17.06 GB/s
Max size of DDR3 RAM?
8 GB
This means that a single RAM module can have a max capacity of 8GB
Data rate of DDR4?
Up to 3200 MT/s
Transfer rate of DDR4?
Up to 25.6 GB/s
Max size of DDR4 RAM?
32 GB
This means that a single RAM module can have a max capacity of 32GB
Data rate of DDR5 RAM?
Up to 6400 MT/s
Transfer rate of DDR5 RAM?
Up to 51.2 GB/s
Max size of DDR5 RAM?
128 GB
This means that a single RAM module can have a max capacity of 128GB
What does the data rate in RAM mean?
i.e. 6400 MT/s
Internal processing speed of the RAM module itself
What is RAM transfer rate?
i.e. 51.2 GBps
Data exchange rate between RAM & other components
Components like the CPU or storage devices
How are RAM modules with the same DDR type & speed differientiated?
Via internal timing characteristics
Expressed in values, like 14-15-15-35 CAS 14
Lower values are better
What is a memory module?
A PCB grouping RAM devices as a single unit
Memory modules are produced in different capacities. Each DDR generation sets an upport limit on the max possible capacity
What memory module do desktops use?
DIMM
The notches on the edge connector identify the DDR generation and ensure proper insertion. DDR DIMMs often have heat sinks due to high clock speeds
Meaning of DIMM?
Dual-Inline Memory Module
What are memory modules vulnerable to?
ESD
Always take anti-ESD precautions when handling & storing these devices
Meaning of ESD?
Electrostatic Discharge
What speeds should memory modules match for optimal performance?
Motherboard’s bus speed
What occurs if memory modules with different speeds are installed on the MOBO?
MOBO = Motherboard
System runs at the speed of the slowest component
What memory modules do laptops use?
SODIMM
Meaning of SODIMM?
Small Outline DIMM
What does single channel memory mean?
Theres 1 64-bit data bus between CPU, memory controller, & RAM
What components need to support multi-channel memory to use it?
“multi-channel” includes dual-, triple-, & quad-channel
- CPU
- Memory controller
- Motherboard
Ordinary RAM modules are used.
What does dual-channel memory mean?
There’s 2 64-bit pathways through the bus to the CPU
This means that 128 bits of data can be sent per transfer rather than 64 bits.
For dual-channel configuration, consult system documentation to find correct slots. Motherboards usually have 4 DIMM slots in color-coded pairs, each pair representing a channel
What may you need to do to use Multi-channel memory?
Enable it via PC’s firmware settings
2 outcomes if a system has an odd number of memory modules?
- Operates in single-channel mode
- Operates in dual-channel mode with the spare module disabled
What memory configuration may a system operate in if memory modules have different capacities?
Operate in flex mode
what happens if the memory configuration is set to flex mode?
Dual-channel is used for the smallest module’s capacity & single-channel for the rest
i.e. if A1 contains a 2GB module & B1 contains a 6GB module, dual-channel mode will be enabled for 2GB of memory & the remaining 4GB from the module in B1 will work in single-channel mode
How do DDR5 memory modules have a different type of data bus?
By having 2 channels of 32 bits
In a dual-channel setup, it forms 4 32-bit channels, improving load distribution, density, and latency, while enhancing compatibility with multi-core CPUs
Meaning of ECC?
Error Correcting Code
When is ECC RAM used?
When high reliability is needed
What does ECC RAM do?
Calculates a hash & stores it with data in memory
The calculated hash is referred to as “checksum”
What does the memory controller in ECC RAM do?
Calculates & compares checksums with stored data
The calculated hash is referred to as “checksum”
Why does the memory controller in ECC RAM calculate & compare checksums?
If the checksums differ, it indicates a data error
The ECC mechanism can correct it if possible
The calculated hash is referred to as “checksum”
Why do ECC RAM modules have an additional processor chip?
To handle data error correction tasks
What data bus width does ECC RAM use?
72-bit
Rather than the standard 64-bit
What errors can ECC RAM detect & correct?
Single-bit errors
It allows the PC to continue funcitoning normally
What errors can ECC RAM detect but not correct?
Errors of 2, 3, or 4 bits
It generates an error message & halts the system for these errors
What are most types of ECC memory modules packaged in?
Registered DIMM (RDIMM) form factors
Some types of ECC RAM are packaged in UDIMMs (Unbuffered DIMMs), but this is rarer
What are most types of non-ECC memory modules packaged in?
Unbuffered DIMM (UDIMM) form factors
How do RDIMMs differ from UDIMMs?
RDIMM = Registered DIMM, UDIMM = Unbuffered DIMM
Use an extra component to reduce electrical load on the memory controller
This has a slight performance penalty, but makes the system more reliable, especially if large amount of memory are installed
3 factors to consider when selecting memory for a system?
- ECC needs MOBO & CPU support
- MOBOs support UDIMMs or RDIMMs, not both (if both are supported, they can’t be mixed)
- Mixing non-ECC & ECC UDIMMs usually fails
Mixing UDIMM & RDIMM modules prevents system booting
DDR5 features internal error checking, distinct from ECC managed by the memory controller, which communicates errors to the CPU. DDR5 includes both non-ECC and ECC variants
