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Data Memory Access - I Cant Be Alone



Modern threats require modern security with a strong alignment between hardware security and software security techniques to keep users, data, and devices protected. The operating system alone cannot protect from the wide range of tools and techniques cybercriminals use to compromise a computer deep inside its silicon. Once inside, intruders can be difficult to detect while engaging in multiple nefarious activities from stealing important data to capturing email addresses and other sensitive pieces of information.These new threats call for computing hardware that is secure down to the very core, including hardware chips and processors. Microsoft and our partners, including chip and device manufacturers, have worked together to integrate powerful security capabilities across software, firmware, and hardware.




Data Memory Access - I Cant Be Alone



PCIe hot plug devices such as Thunderbolt, USB4, and CFexpress allow users to attach classes of external peripherals, including graphics cards, to their devices with the plug-and-play ease of USB.These devices are DMA-capable, and can access system memory and perform read and write operations without the need for the system processor's involvement. This capability is the reason behind the exceptional performance of PCI devices, but it also makes them susceptible to drive-by DMA attacks.


RAM (Random Access Memory) is the hardware in a computing device where the operating system (OS), application programs and data in current use are kept so they can be quickly reached by the device's processor. RAM is the main memory in a computer. It is much faster to read from and write to than other kinds of storage, such as a hard disk drive (HDD), solid-state drive (SSD) or optical drive.


Because of its volatility, RAM can't store permanent data. RAM can be compared to a person's short-term memory, and a hard disk drive to a person's long-term memory. Short-term memory is focused on immediate work, but it can only keep a limited number of facts in view at any one time. When a person's short-term memory fills up, it can be refreshed with facts stored in the brain's long-term memory.


The term random access as applied to RAM comes from the fact that any storage location, also known as any memory address, can be accessed directly. Originally, the term Random Access Memory was used to distinguish regular core memory from offline memory.


Offline memory typically referred to magnetic tape from which a specific piece of data could only be accessed by locating the address sequentially, starting at the beginning of the tape. RAM is organized and controlled in a way that enables data to be stored and retrieved directly to and from specific locations.


A hard drive, on the other hand, stores data on the magnetized surface of what looks like a vinyl record. Alternatively, an SSD stores data in memory chips that, unlike RAM, are nonvolatile. They don't depend on having constant power and won't lose data once the power is turned off. RAM microchips are gathered together into memory modules. These plug into slots in a computer's motherboard. A bus, or a set of electrical paths, is used to connect the motherboard slots to the processor.


Most PCs enable users to add RAM modules up to a certain limit. Having more RAM in a computer cuts down on the number of times the processor must read data from the hard disk, an operation that takes longer than reading data from RAM. RAM access time is in nanoseconds, while storage memory access time is in milliseconds.


With virtual memory, data is temporarily transferred from RAM to disk storage, and virtual address space is increased using active memory in RAM and inactive memory in an HDD to form contiguous addresses that hold an application and its data. Using virtual memory, a system can load larger programs or multiple programs running at the same time, letting each operate as if it has infinite memory without having to add more RAM.


Virtual memory is able to handle twice as many addresses as RAM. A program's instructions and data are initially stored at virtual addresses, and once the program is executed, those addresses are turned into actual memory addresses.


Flash memory and RAM are both comprised of solid-state chips. However, they play different roles in computer systems because of differences in the way they're made, their performance specifications and cost. Flash memory is used for storage memory. RAM is used as active memory that performs calculations on the data retrieved from storage.


One significant difference between RAM and flash memory is that data must be erased from NAND flash memory in entire blocks. This makes it slower than RAM, where data can be erased in individual bits.


However, NAND flash memory is less expensive than RAM, and it's also nonvolatile. Unlike RAM, it can hold data even when the power is off. Because of its slower speed, nonvolatility and lower cost, flash is often used for storage memory in SSDs.


Read-only memory, or ROM, is computer memory containing data that can only be read, not written to. ROM contains boot-up programming that is used each time a computer is turned on. It generally can't be altered or reprogrammed.


The data in ROM is nonvolatile and isn't lost when the computer power is turned off. As a result, read-only memory is used for permanent data storage. Random Access Memory, on the other hand, can only hold data temporarily. ROM is generally several megabytes of storage, while RAM is several gigabytes.


In February 2019, the JEDEC Solid State Technology Association published the JESD209-5, Low Power Double Data Rate 5 (LPDDR5). LPDDR5 will eventually operate at an I/O rate of 6400 MT/s, 50 percent higher than that of the first version of LPDDR4. This will significantly boost memory speed and efficiency for a variety of applications. This includes mobile computing devices such as smartphones, tablets and ultra-thin notebooks.


The reason for this bug is that the data used by the create_array function is a local variable that only exists inside that function. The assigned memory address obtained from malloc is only stored in this local variable and never returned to the caller.


Random access memory (RAM) is the best-known form of computer memory. This is what allows your computer to surf the internet and then quickly switch to loading an application or editing a document. RAM is considered "random access" because you can access any memory cell directly if you know the row and column that intersect at that cell.


In contrast, serial access memory (SAM) stores data as a series of memory cells that can only be accessed sequentially (like a cassette tape). If the data is not in the current location, each memory cell is checked until the needed data is found. SAM works very well for memory buffers, where the data is normally stored in the order in which it will be used (for instance, the texture buffer memory on a video card). RAM data, on the other hand, can be accessed in any order.


DRAM works by sending a charge through the appropriate column (CAS) to activate the transistor at each bit in the column. When writing, the row lines contain the state the capacitor should take on. When reading, the sense-amplifier determines the level of charge in the capacitor. If it is more than 50 percent, it reads it as a 1; otherwise it reads it as a 0. The counter tracks the refresh sequence based on which rows have been accessed in what order. The length of time necessary to do all this is so short that it is expressed in nanoseconds (billionths of a second). A memory chip rating of 70ns means that it takes 70 nanoseconds to completely read and recharge each cell.


Memory cells alone would be worthless without some way to get information in and out of them. So, the memory cells have a whole support infrastructure of other specialized circuits. These circuits perform functions such as:


Static RAM uses a completely different technology. In static RAM, a form of flip-flop holds each bit of memory (see How Boolean Logic Works for details on flip-flops). A flip-flop for a memory cell takes four or six transistors along with some wiring, but never has to be refreshed. This makes static RAM significantly faster than dynamic RAM. However, because it has more parts, a static memory cell takes up a lot more space on a chip than a dynamic memory cell. Therefore, you get less memory per chip, and that increases its price.


Most memory available today is highly reliable. Most systems simply have the memory controller check for errors at startup and rely on that. Memory chips with built-in error-checking typically use a method known as parity to check for errors. Parity chips have an extra bit for every 8 bits of data. The way parity works is simple. Let's look at even parity first.


When working with threads in Python, you will find very useful to be able to share data between different tasks. One of the advantages of threads in Python is that they share the same memory space, and thus exchanging information is relatively easy. However, some structures can help you achieve more specific goals.


The important piece of code in this example is the print(my_var) line.That print statement lives in the main thread, however, it has access tothe information being generated within a child thread. This behavior ispossible thanks to memory sharing between different threads. Being ableto access the same memory space is useful, but it can also pose somerisks. In the example above, we have started only one thread, but we arenot limited to that. We could, for example, start several threads:


Note that we added a line with data_lock: to the function. If you runthe code again, you will see that the values we get are alwaysconsecutive. The lock guarantees that only one thread will access thevariable at a time.


!!! warningit is a very wise idea to be sure a queue is empty after you stop using it. If, as before, you interrupt the thread by looking at the status of a lock, the queue may be left with a lot of data in it, and thus the memory will not be freed. A simple while-loop that gets all the elements of a queue solves it. 041b061a72


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