Memory Reading Journal

There are two main types of memory known as RAM and ROM, RAM is random access memory while ROM is read only memory. While both types of memory can be found on adapters ROM is characterized by being non volatile which means the data stored on it is not deleted unlike the volatile memory of the RAM. RAM also differs from ROM as it can be changed, stores the data for currently running applications, is located on the motherboard and houses part of the system’s os.

There are two types of RAM, dynamic RAM(DRAM) and static RAM(SRAM). DRAM is less expensive than SRAM but is also slower. One of the reasons for DRAM being slower is that it has to refresh the charge inside the memory that represents the data due to the charge leaking over time. This refreshing process occurs while other processes are running inside the memory. A majority of the memory storage on the motherboard is DRAM but some of it is SRAM stored inside and around the processor itself and occasionally on the motherboard.Another name for SRAM is cache memory. The data that is most frequently needed is stored on SRAM as it is the fastest memory available to the CPU. The order for both speed and where the CPU looks for stored data is cache memory, DRAM and then the hard drive.

There are many types of DRAM. Some of the various kinds of DRAM is Synchronous DRAM(SDRAM) where the memory operations are performed in short bursts and are aligned with the CPU clock signal. The Double Data Rate(DDR) which is able to send twice the data as PC133 SDRAM due to its ability to send data on both sides of the clock signal. The DDR series contains the DDR, DDR2, DDR3, DDR3L, DD4 and the DDR4L. The two DDRs that have Ls are able to run at lower voltages. The DDR2 and 3 use 240-pin DIMMS while the DDR4 uses 288. None of the DDRs versions are compatible with each other despite some of them using the same number of pins. Even the DDRs that use the same number of pins can't fit into a memory slot meant for the other. Each new DDRs was faster and more efficient than the last version. It is hard to differentiate between the DDR memory modules due to them all being the same size.

A chipset is the piece of hardware on the motherboard that determines what memory chips are supported. The chipset can be one to five electronic chips on a motherboard and has the hardware that controls the local bus, memory, DMA, interrupts and cache memory. DIMMS are listed by a name with the prefix that is either PCX- or DDRX-. The number that follows the PCX is how much bandwidth the memory chip has in MB/s in theory while the number after DDRX is double the clock speed.

There are many features that a memory module can possess such as their ability to check and correct errors, how efficiently they can store information and how fast information is processed. The two kinds of memory checking that a memory module may have are parity and error correcting code(ECC). Parity checks to make sure that the number of 1s is either even or odd depending on what kind of parity is being used. ECC uses a mathematical algorithm to ensure that data is accurate and can find memory errors in up to 4-bit and correct 1-bit memory errors. A feature that can affect how quickly memory is sent is whether it is unbuffered memory or buffered memory(registered memory). Buffered money has extra chips, also known as registers around the bottom of the chip that hold back the transmission of data by one clock tick to ensure that the data being sent is accurate. Unbuffered memory does not do this which allows it to be faster. The memory available on each module is dependent on whether it is single-sided or double sided. A single sided memory module transfers data in 64 bits to the CPU and the chips that store the data may be on one or both sides of the memory module. Double sided memory has two memory modules within one housing so that it can hold twice as much information. A computer that is designed to accept this kind of memory still transmits in 64 bits but can hold twice as much memory with the same amount of slots. Some other features that memory can have is serial presence detect(SPD) which has information about the DIMM and allows the BIOS/UEFI to use that data to operate more efficiently. Another feature that memory can have is called dual-voltage memory which is able to operate at lower voltages which allows for less heat to be produced. If the system is to operate in low voltage mode then all modules have to be able to run on lower voltage. Extreme memory profile(XMP) allows the BIOS to overclock the memory by configuring the settings of the voltage and timing.

Virtual memory is a way of using hard drive space as if it were RAM. When using virtual memory, operating systems can run larger or more applications at the same time than it could without virtual memory. The section of space that an application uses on the hard drive as if it were RAM is called a swap file which is also known as page file or paging file. While a system is using virtual memory, the use of hard drive space is dynamic and changes as the memory needs change. If a system has multiple hard drives then the swap file should be stored on the fastest hard drive that has adequate available space and doesn’t contain the OS. On a system using 32-bit windows uses 32-bit demand paged virtual memory which allocates 4GB of address space that is split into a pair of 2GB sections. One of the sections is shared with the rest of the system while the other half is strictly for the application. The system sorts the memory into 4KB chunks called pages. The OS gives as much possible RAM to an application before swapping it in and out of the swap file as needed automatically. Physical address extension can be used on some motherboards which increases the amount of physical memory available to 64GB or 128GB. PAEs are only relevant to 32-bit systems. 64-bit systems dont evenly split their virtual memory but instead limits each application to 8TB.

Task manager can be used to monitor memory usage under its performance tab. The section allows the monitoring of things ranging from the amount of RAM installed to how many processes are running to how long the device has been running. The memory section in the performance tab provides any information that could be needed such as some of the priorly stated stats along with more information about how memory is divided.

Flash memory is a nonvolatile, solid state memory. PCs can replace the BIOS chip with flash memory. Some devices such as smartphones, tablets and other networking devices use flash memory to store their operating system and instructions. Some devices like digital cameras and scanners use flash memory to store what they produce while some printers use flash memory to store information for printing such as fonts. USB flash drives, which are also called thumb drives, memory bars and memory sticks, can store up to 256GB and connect to devices via usb. Windows is able to automatically recognize USB flash drives and give them a drive letter so data can be copied to them from File Explorer. Some flash drives provide protection in the form of passwords or data encryption. It is important to remember to either turn off the device or ensure that the device is properly ejected before it is removed or else the drive and data could be damaged.

Source: Schmidt, Cheryl A. “6. Memory.” Complete Comptia A+ Guide to It Hardware and Software, 7th ed., Pearson It Certification, Indianapolis, Indiana, 2016.