Computer memory is a device or system that is used to store information for immediate use in a computer or related computer hardware and digital electronic devices. The term memory is often synonymous with the term primary storage or main memory. An archaic synonym for memory is store. Main memory is the primary, internal workspace in the computer, commonly known as RAM (random access memory). Specifications such as 4GB, 8GB, 12GB, and 16GB almost always refer to the capacity of RAM. In contrast, disk or solid-state storage capacities in a computer are typically 128GB or 256GB and higher. Memory is made up of bits arranged in a two-dimensional grid. In this figure, red cells represent 1s and white cells represent 0s. In the animation, a column is selected and then rows are charged to write data into the specific column.
At the beginning of the production process, bare silicon wafers are covered with a thin layer of glass, followed by a nitride layer. The glass layer is formed by exposing the silicon wafer to oxygen at temperatures of 900 degrees Celsius for an hour or more, depending on how thick the layer needs to be.
Computer memory is divided into main (or primary) memory and auxiliary (or secondary) memory. Main memory holds instructions and data when a program is executing, while auxiliary memory holds data and programs not currently in use and provides long-term storage.
The computer memory holds the data and instructions needed to process raw data and produce output. The computer memory is divided into a large number of small parts known as cells. Each cell has a unique address that varies from 0 to memory size minus one.
Computer memory is of two types
Volatile (RAM) and Non-volatile (ROM). The secondary memory (hard disk) is referred to as storage, not memory.
But, if we categorize memory on behalf of space or location, it is of four types:
- Register memory
- Cache memory
- Primary memory
- Secondary memory
Register Memory
Register memory is the smallest and fastest memory in a computer. It is not a part of the main memory and is located in the CPU in the form of registers, which are the smallest data holding elements. A register temporarily holds frequently used data, instructions, and memory addresses that are to be used by the CPU. They hold instructions that are currently processed by the CPU. All data is required to pass through registers before it can be processed. So, they are used by the CPU to process the data entered by the users.
Registers hold a small amount of data around 32 bits to 64 bits. The speed of a CPU depends on the number and size (no. of bits) of registers that are built into the CPU. Registers can be of different types based on their uses. Some of the widely used Registers include Accumulator or AC, Data Register or DR, the Address Register or AR, Program Counter (PC), I/O Address Register, and more.
Types and Functions of Computer Registers
- Data Register: It is a 16-bit register, which is used to store operands (variables) to be operated by the processor. It temporarily stores data, which is being transmitted to or received from a peripheral device.
- Program Counter (PC): It holds the address of the memory location of the next instruction, which is to be fetched after the current instruction is completed. So, it is used to maintain the path of execution of the different programs and thus executes the programs one by one, when the previous instruction gets completed.
- Instructor Register: It is a 16-bit register. It stores the instruction which is fetched from the main memory. So, it is used to hold instruction codes, which are to be executed. The Control Unit takes instruction from the Instructor Register, then decodes and executes it.
- Accumulator Register: It is a 16-bit register, which is used to store the results produced by the system. For example, the results generated by the CPU after the processing are stored in the AC register.
- Address Register: It is a 12-bit register that stores the address of a memory location where instructions or data are stored in the memory.
- I/O Address Register: Its job is to specify the address of a particular I/O device.
- I/O Buffer Register: Its job is to exchange the data between an I/O module and the CPU.
Cache Memory
Cache memory is a high-speed memory, which is small in size but faster than the main memory (RAM). The CPU can access it more quickly than the primary memory. So, it is used to synchronize with a high-speed CPU and to improve its performance.
Cache memory can only be accessed by the CPU. It can be a reserved part of the main memory or a storage device outside the CPU. It holds the data and programs which are frequently used by the CPU. So, it makes sure that the data is instantly available for the CPU whenever the CPU needs this data. In other words, if the CPU finds the required data or instructions in the cache memory, it doesn’t need to access the primary memory (RAM). Thus, by acting as a buffer between RAM and CPU, it speeds up the system performance.
Types of Cache Memory
- L1: It is the first level of cache memory, which is called Level 1 cache or L1 cache. In this type of cache memory, a small amount of memory is present inside the CPU itself. If a CPU has four cores (quad-core CPU), then each core will have its level 1 cache. As this memory is present in the CPU, it can work at the same speed as the CPU. The size of this memory ranges from 2KB to 64 KB. The L1 cache further has two types of caches: The instruction cache, which stores instructions required by the CPU, and the data cache which stores the data required by the CPU.
- L2: This cache is known as Level 2 cache or L2 cache. This level 2 cache may be inside the CPU or outside the CPU. All the cores of a CPU can have their separate level 2 cache, or they can share one L2 cache among themselves. In case it is outside the CPU, it is connected to the CPU with a very high-speed bus. The memory size of this cache is in the range of 256 KB to 512 KB. In terms of speed, they are slower than the L1 cache.
- L3: It is known as Level 3 cache or L3 cache. This cache is not present in all the processors; some high-end processors may have this type of cache. This cache is used to enhance the performance of Level 1 and Level 2 cache. It is located outside the CPU and is shared by all the cores of a CPU. Its memory size ranges from 1 MB to 8 MB. Although it is slower than L1 and L2 cache, it is faster than Random Access Memory (RAM).
How does cache memory work with CPU?
When the CPU needs the data, first of all, it looks inside the L1 cache. If it does not find anything in L1, it looks inside the L2 cache. If again, it does not find the data in the L2 cache, it looks into the L3 cache. If data is found in the cache memory, then it is known as a cache hit. On the contrary, if data is not found inside the cache, it is called a cache miss.
If data is not available in any of the cache memories, it looks inside the Random Access Memory (RAM). If RAM also does not have the data, then it will get that data from the Hard Disk Drive.
So, when a computer is started for the first time, or an application is opened for the first time, data is not available in cache memory or RAM. In this case, the CPU gets the data directly from the hard disk drive. Thereafter, when you start your computer or open an application, the CPU can get that data from cache memory or RAM.
Primary Memory
Primary Memory is of two types: RAM and ROM.
RAM (Volatile Memory)
It is a volatile memory. It means it does not store data or instructions permanently. When you switch on the computer the data and instructions from the hard disk are stored in RAM. CPU utilizes this data to perform the required tasks. As soon as you shut down the computer the RAM loses all the data.
ROM (Non-volatile Memory)
It is a non-volatile memory. It means it does not lose its data or programs that are written on it at the time of manufacture. So it is a permanent memory that contains all important data and instructions needed to perform important tasks like the boot process.
Now we discuss each type of memory one by one in detail
It is also known as the main memory of the computer system. It is used to store data and programs or instructions during computer operations. It uses semiconductor technology and hence is commonly called semiconductor memory. Primary memory is of two types:
(i) RAM (Random Access Memory): It is a volatile memory. Volatile memory stores information based on the power supply. If the power supply fails/is interrupted/stopped, all the data & information on this memory will be lost. RAM is used for booting up or starting the computer. It temporarily stores programs/ data which has to be executed by the processor. RAM is of two types:
- S RAM (Static RAM): It uses transistors and the circuits of this memory are capable of retaining their state as long as the power is applied. This memory consists of the number of flip flops with each flip flop storing 1 bit. It has less access time and hence, it is faster.
- D RAM (Dynamic RAM): It uses capacitors and transistors and stores the data as a charge on the capacitors. They contain thousands of memory cells. It needs refreshing of charge on capacitor after a few milliseconds. This memory is slower than S RAM.
(ii) ROM (Read Only Memory): It is a non-volatile memory. Non-volatile memory stores information even when there is a power supply failed/ interrupted/stopped. ROM is used to store information that is used to operate the system. As its name refers to read-only memory, we can only read the programs and data that are stored on it. It contains some electronic fuses that can be programmed for a piece of specific information. The information stored in the ROM is in binary format. It is also known as permanent memory. ROM is of four types:
- MROM(Masked ROM): Hard-wired devices with a pre-programmed collection of data or instructions were the first ROMs. Masked ROMs are a type of low-cost ROM that works in this way.
- PROM (Programmable Read-Only Memory): This read-only memory is modifiable once by the user. The user purchases a blank PROM and uses a PROM program to put the required contents into the PROM. Its content can’t be erased once written.
- EPROM (Erasable Programmable Read-Only Memory): It is an extension to PROM where you can erase the content of ROM by exposing it to Ultraviolet rays for nearly 40 minutes.
- EEPROM (Electrically Erasable Programmable Read-Only Memory): Here the written contents can be erased electrically. You can delete and reprogramme EEPROM up to 10,000 times. Erasing and programming take very little time, i.e., nearly 4 -10 ms(milliseconds). Any area in an EEPROM can be wiped and programmed selectively.
Secondary Memory
It is also known as auxiliary memory and backup memory. It is a non-volatile memory and is used to store a large amount of data or information. The data or information stored in secondary memory is permanent, and it is slower than in primary memory. A CPU cannot access secondary memory directly. The data/information from the auxiliary memory is first transferred to the main memory, and then the CPU can access it.
Characteristics of Main Memory
- It is a slow memory but reusable.
- It is a reliable and non-volatile memory.
- It is cheaper than primary memory.
- The storage capacity of secondary memory is large.
- A computer system can run without secondary memory.
- In secondary memory, data is stored permanently even when the power is off.
Types of secondary memory
- (i) Magnetic Tapes: Magnetic tape is a long, narrow strip of plastic film with a thin, magnetic coating on it that is used for magnetic recording. Bits are recorded on tape as magnetic patches called RECORDS that run along many tracks. Typically, 7 or 9 bits are recorded concurrently. Each track has one read/write head, which allows data to be recorded and read as a sequence of characters. It can be stopped, started moving forward or backward, or rewound.
- (ii) Magnetic Disks: A magnetic disc is a circular metal or a plastic plate and these plates are coated with magnetic material. The disc is used on both sides. Bits are stored in magnetized surfaces in locations called tracks that run in concentric rings. Sectors are typically used to break tracks into pieces. Hard discs are discs that are permanently attached and cannot be removed by a single user.
- (iii) Optical Disks: It’s a laser-based storage medium that can be written to and read. It is reasonably priced and has a long lifespan. The optical disc can be taken out of the computer by occasional users. Types of Optical Disks
Hard Disk
It is a rigid magnetic disc that is used to store data. It permanently stores data and is located within a drive unit
The hard disk is also known as a hard drive. It is a rigid magnetic disc that stores data permanently, as it is a non-volatile storage device. The hard disk is located within a drive unit on the computer’s motherboard and comprises one or more platters packed in an air-sealed casing. The data is written on the platters by moving a magnetic head over the platters as they spin. The data stored on a computer’s hard drive generally includes the operating system, installed software, and the user’s files and programs, including pictures, music, videos, text documents, etc.
Components of Hard Drive
The main components of a hard drive include a head actuator, read/write actuator arm, read/write head, platter, and spindle. A circuit board, which is called the disk controller or interface board, is present on the back of a hard drive. It allows the hard drive to communicate with the computer.
Solid-state Drive
SSD (Solid State Drive) is also a non-volatile storage medium that is used to hold and access data. Unlike a hard drive, it does not have moving components, so it offers many advantages over SSD, such as faster access time, noiseless operation, less power consumption, and more.
As the cost of SSD has come down, it has become an ideal replacement for a standard hard drive in desktop and laptop computers. It is also suitable for notebooks, and tablets that don’t require lots of storage.
Pen drive
A pen drive is a compact secondary storage device. It is also known as a USB flash drive, thumb drive, or jump drive. It connects to a computer via a USB port. It is commonly used to store and transfer data between computers. For example, you can write a report using a computer and then copy or transfer it in a pen drive. Later, you can connect this pen drive to a computer to see or edit your report. You can also store your important documents and pictures, music, and videos in the pen drive and keep it in a safe place.
Pen drive does not have movable parts; it comprises an integrated circuit memory chip that stores the data. This chip is housed inside a plastic or aluminum casing. The data storage capacity of the pen drive generally ranges from 2 GB to 128 GB. Furthermore, it is a plug and play device as you don’t need additional drives, software, or hardware to use it.
SD Card
SD Card stands for Secure Digital Card. It is most often used in portable and mobile devices such as smartphones and digital cameras. You can remove it from your device and see the things stored in it using a computer with a card reader.
There are many memory chips inside the SD card that store the data; it does not have moving parts. SD cards are not created equal, so they may differ from each other in terms of speed, physical sizes, and capacity. For example, standard SD cards, mini SD cards, and micro SD cards.
Compact Disk (CD)
A compact Disk is a portable secondary storage device in the shape of a round medium disk. It is made of polycarbonate plastic. The concept of the CD was co-developed by Philips and Sony in 1982. The first CD was created on 17 August 1982 at the workshop of Philips in Germany.
In the beginning, it was used for storing and playing sound recordings, later it was used for various purposes such as for storing documents, audio files, videos, and other data like software programs in a CD.
Physical characteristics of a CD/ Structure of CD
A standard CD is around 5 inches in diameter and 0.05 inches in thickness. It is made of a clear polycarbonate plastic substrate, a reflective metallic layer, and a clear coating of acrylic plastic. These thin circular layers are attached one on top of another as described below:
- A polycarbonate disc layer at the bottom has the data encoded by creating lands and pits.
- The polycarbonate disc layer is coated with a thin aluminum layer that reflects the laser.
- The reflective aluminum layer is coated with a lacquer layer to prevent oxidation in order to protect the below layers. It is generally spin coated directly on the top of the reflective layer.
- The label print is applied on the lacquer layer, or artwork is screen printed on the top of the disc on the lacquer layer by offset printing or screen printing.
How Does a CD Work?
The data or information is stored or recorded or encoded in CD digitally using a laser beam that etches tiny indentations or bumps on its surface. The bump is called a pit, which represents the number 0. Space, where the bump is not created, is called land, and it represents the number 1. Thus, the data is encoded into a compact disc by creating pits (0) and lands (1). The CD players use laser technology to read the optically recorded data.
(a) CD – ROM
- It’s called Compact Disk. Only read from memory.
- Information is written to the disc by using a controlled laser beam to burn pits on the disc surface.
- It has a highly reflecting surface, which is usually aluminum.
- The diameter of the disc is 5.25 inches.
- 16000 tracks per inch are the track density.
- The capacity of a CD-ROM is 600 MB, with each sector storing 2048 bytes of data.
- The data transfer rate is about 4800KB/sec. & the new access time is around 80 milliseconds.
(b) WORM-(WRITE ONCE READ MANY)
- A user can only write data once.
- The information is written on the disc using a laser beam.
- It is possible to read the written data as many times as desired.
- They keep lasting records of information but access time is high.
- It is possible to rewrite updated or new data to another part of the disc.
- Data that has already been written cannot be changed.
- Usual size – 5.25 inch or 3.5-inch diameter.
- The usual capacity of a 5.25-inch disk is 650 MB,5.2GB, etc.
(c) DVDs
- The term “DVD” stands for “Digital Versatile/Video Disc,” and there are two sorts of DVDs: (i)DVDR (writable) and (ii) DVDRW (Re-Writable)
- DVD-ROMS (Digital Versatile Discs): These are read-only memory (ROM) discs that can be used in a variety of ways. When compared to CD-ROMs, they can store a lot more data. It has a thick polycarbonate plastic layer that serves as a foundation for the other layers. It’s an optical memory that can read and write data.
- DVD-R: It is a writable optical disc that can be used just once. It’s a DVD that can be recorded. It’s a lot like WORM. DVD-ROMs have capacities ranging from 4.7 to 17 GB. The capacity of the 3.5-inch disk is 1.3 GB.
DVDs can be divided into three main categories which are as follows:
- DVD-ROM (Read-Only): These types of DVDs come with media already recorded on them, such as movie DVDs. As the name suggests, data on these discs cannot be erased or added, so these discs are known as read-only or non-writable DVDs.
- DVD-R (Writable): It allows you to record or write information on the DVD. However, you can write information only once as it becomes a read-only DVD once it is full.
- DVD-RW (Rewritable or Erasable): This type of disc can be erased, written, or recorded multiple times.
Memory Units
Memory units are used to measure and represent data. Some of the commonly used memory units are:
- Bit: The computer memory units start from bit. A bit is the smallest memory unit to measure data stored in main memory and storage devices. A bit can have only one binary value out of 0 and 1.
- Byte: It is the fundamental unit to measure data. It contains 8 bits or is equal to 8 bits. Thus a byte can represent 2*8 or 256 values.
- Kilobyte: A kilobyte contains 1024 bytes.
- Megabyte: A megabyte contains 1024 kilobytes.
- Gigabyte: A gigabyte contains 1024 megabytes.
- Terabyte: A terabyte contains 1024 gigabytes.
How Are RAM and Memory Made?
Ever wondered what RAM is made of and how memory is manufactured? Here’s a behind-the-scenes look at the rigorous process we undertake to manufacture memory and ensure that you get a high-quality product.
Part I: From silicon to finished wafer
Memory chips are integrated circuits with various transistors, resistors, and capacitors that must be formed on each chip. These integrated circuits begin with silicon, which is usually extracted from sand. Turning silicon into memory chips is an exacting, meticulous procedure involving engineers, metallurgists, chemists, and physicists. Memory is produced in a large facility called a fab, which contains many cleanroom environments. Semiconductor memory chips are manufactured in cleanrooms because the circuitry is so small that even tiny bits of dust can damage it. Micron’s main facility in Boise, Idaho covers over 1.8 million square feet and has class 1 and class 10 clean rooms. In a class 1 cleanroom, there is no more than 1 particle of dust in a cubic foot of air. In comparison, a clean, modern hospital has about 10,000 dust particles per cubic foot of air. The air inside a cleanroom is filtered and circulated continuously. Production team members wear special caps, gowns, and masks that help keep the air particle-free.
Step 1: Silicon ingots
The first step from silicon to integrated circuit is the creation of a pure, single-crystal cylinder, or ingot, that is made of silicon and that measures 330 millimeters in diameter. After they’re formed, silicon ingots are sliced into thin, highly polished wafers less than six millimeters thick. The circuit elements of the chip (transistors, resistors, and capacitors) are then constructed in layers on the silicon wafer. Circuits are developed, tested by simulation, and perfected on computer systems before they are actually built. When the design is complete, glass photomasks are made—one mask for each layer of the circuit. Photomasks are opaque plates with holes or transparencies that allow light to shine through in a defined pattern, and these masks are essential to the next step in the manufacturing process: photolithography.
Step 2: Photolithography
In the sterile clean-room environment, wafers are exposed to a multi-step photolithography process which is repeated once for each mask required by the circuit. Masks are used (a) to define the different parts of a transistor, capacitor, resistor, or connector that will complete the integrated circuit, and (b) to define the circuitry pattern for each layer on which the device is fabricated. At the beginning of the production process, bare silicon wafers are covered with a thin layer of glass, followed by a nitride layer. The glass layer is formed by exposing the silicon wafer to oxygen at temperatures of 900 degrees Celsius for an hour or more, depending on how thick the layer needs to be. Glass (silicon dioxide) is formed when the silicon material in the wafer is exposed to oxygen. At high temperatures, this chemical reaction (called oxidation) occurs at a very fast rate.
Step 3: Photoresist
Next, the wafer is uniformly coated with a thick, light-sensitive liquid called a photoresist. Portions of the wafer are selected for exposure by carefully aligning a mask between an ultraviolet light source and the wafer. In the transparent areas of the mask, light passes through and exposes the photoresist. When exposed to ultraviolet light, the photoresist undergoes a chemical change, which allows a developer solution to remove the exposed photoresist and leave an unexposed portion on the wafer. For each mask required by the circuit, the photolithography/photoresist process is repeated.
Step 4: Etch
In the etch step, wet acid or plasma dry gas is placed on the wafer to remove the portion of the nitride layer that is unprotected by the hardened photoresist. This leaves a nitride pattern on the wafer in the exact design of the mask. When the hardened photoresist is removed (cleaned) with another chemical, hundreds of memory chips can now be etched onto the wafer.
Part II: Layering the wafer and completing the circuit
In Part, I of the manufacturing process, all of the circuit elements (transistors, resistors, and capacitors) were constructed during the initial mask operations. The next steps connect these elements together by creating a set of layers.
Step 5: Aluminum layering
To begin connecting the circuit elements together, an insulating layer of glass (called BPSG) is deposited on the wafer, and a contact mask is used to define the contact points (or windows) of each of the circuit elements. After contact windows are etched, the entire wafer is covered with a thin layer of aluminum in a sputtering chamber. When a metal mask is applied to the aluminum layer, a network of thin metal connections or wires is formed, creating a path for the circuit.
Step 6: Passivation layering
The entire wafer is then covered with an insulating layer of glass and silicon nitride to protect it from contamination during assembly. This protective coating is called the passivation layer. A final mask and passivation etch process follows, removing the passivation material from terminals, which are called bonding pads. The now-free bonding pads are used to electrically connect the die to metal pins on the plastic or ceramic package, and the integrated circuit is now complete. Before the wafer is sent to die assembly, every integrated circuit on the wafer is tested. Functional and nonfunctional chips are identified and mapped into a computer data file. A diamond saw then cuts the wafer into individual chips. Nonfunctional chips are discarded and the rest are ready to be assembled. These individual chips are referred to as die. Before the die is encapsulated, they are mounted to lead frames where thin gold wires connect the bonding pads on the chip to the frames to create an electrical path between the die and lead fingers.
Part III: Die preparation and testing
In Part II of the manufacturing process, the integrated circuit was created and the finished wafer was cut into dies. The next steps prepare the die for use in finished modules.
Step 7: Encapsulation
During encapsulation, lead frames are placed onto mold plates and heated. Molten plastic material is pressed around each die to form its individual package. The mold is opened, and the lead frames are pressed out and cleaned.
Step 8: Electroplating
Electroplating is the next process where the encapsulated lead frames are “charged” while submerged in a solution of tin and lead. Here, the tin and lead ions are attracted to the electrically charged lead frame, which creates a plated uniform deposit, increasing the conductivity of the die and providing a clean surface so that the die can be mounted.
Step 9: Trim and form
In trim and form, lead frames are loaded into trim-and-form machines, where leads are formed and the chips are then severed from the frames. Individual chips are then put into antistatic tubes for handling and transportation to the test area for final testing.
Step 10: Burn-in testing
In burn-in testing, every chip is tested to see how it performs under accelerated stress conditions. Burn-in testing is a critical component of module reliability. By testing modules in accelerated stress conditions, we’re able to weed out the few modules in every batch that will fail after minimal use. To conduct burn-in testing, we use industry-leading AMBYX ovens that our engineers developed specifically for burn-in testing. After memory chips pass burn-in testing, they are inspected, sealed, and ready to be assembled.
Step 11: PCB assembly and construction
After memory chips are made, they need a way to be connected to your computer’s motherboard. Printed circuit boards (PCBs) solve this problem by providing a way to connect the chips to the motherboard. To accomplish this, chips are mounted to a printed circuit board (PCB) and the final product is a finished memory module. PCBs are built-in arrays, or sheets, which are made up of several identical boards. After assembly, the array gets separated into individual modules, similar to how a chocolate bar can be broken into smaller squares. By varying the total number of PCBs in each array based on size, Micron maximizes the number of modules made from a given amount of raw materials.
Part IV: Module assembly
In Part III of the manufacturing process, the die and PCB were prepared for final module assembly. The final steps cover the module assembly process.
Step 12: Screenprint
When the module design is perfected and the PCBs produced, memory module assembly begins! Assembly entails an intricate soldering procedure that attaches memory chips to the PCB. This begins with screen printing. In screen printing, a stencil is used to screen solder paste onto the finished PCB. Solder paste is a tacky substance that holds chips in place on the PCB. The use of the stencil ensures that solder paste affixes only where components (chips) will attach. The points of attachment are easy to find, thanks to fiducials, which are marks on the PCB that determine where chips need to be placed. Once the solder paste has been applied, automated “pick and place” assembly machines scan the fiducials to determine where to place chips on the PCB. Pick and place machines are programmed to know which chips are placed where, so when a machine picks a chip from a feeder and places it on the PCB, it knows exactly where the chip is at. The chip placement process occurs for all remaining chips and for any other components on the module. Of all the steps in memory manufacturing, this is the fastest: chips are placed on the finished PCB in just a few seconds!
Step 13: Soldering and attachment
Next, the assembled chips and boards pass through an oven. The heat melts the solder paste into a liquid. When the solder cools, it solidifies, leaving a permanent bond between the memory chips and the PCB. The surface tension of the molten solder prevents the chips from misaligning during this process. After the chips are attached, the array is separated into individual modules. Micron team members visually inspect each module. Many modules also undergo additional inspections using automated X-ray equipment to ensure that all joints have been soldered properly. All Micron memory modules meet IPC-A-610 acceptance criteria – the industry standard recognized worldwide.
Step 14: Post-assembly quality testing
Micron then tests and tags the modules. We use custom equipment to automatically test performance and functionality. This eliminates any possibility of an operator mistakenly placing a failed module in a passing location. Certain modules are programmed with an identifying “Dog Tag” that your PC will recognize and read.
Step 15: Shipment
Before being sent out to computer manufacturers and consumers, a statistically significant portion of finished modules is randomly selected for a final quality inspection. After modules are approved for use, they are placed into ESD-safe plastic trays and bags and are made ready for delivery. After an extensive manufacturing process, your memory is ready for use. It’s been rigorously tested and approved!
To determine the right kind of memory for your computer, use the Crucial® Advisor™ tool or System Scanner tool. These tools will help you determine which memory modules are compatible with your computer, along with options for your speed requirements and budget. Keep reading to learn more about those options.
SRAM, DRAM, and ECC
Static random access memory (SRAM) and dynamic access memory (DRAM) are two classifications of memory. With SRAM, data is stored using a six transistor memory cell. SRAM is frequently used as cache memory for the processor (CPU) and is not typically user-replaceable.
DRAM stores data using a transistor and capacitor pair, which make up a single DRAM cell. DRAM is less expensive to produce, but is slightly slower than SRAM. Most user-replaceable memory modules are DRAM.
Error-correcting code (ECC) is a type of DRAM that has an additional cell to detect and correct random faults. ECC memory is user-replaceable, but it needs to be compatible with the other computer hardware.
Data Rates: DDR Explained
SDRAM (synchronous dynamic random access memory) was developed in response to increased speed in other computer components. Previously, memory had to be asynchronous, that is, it operated independently of the processor. Synchronous memory synchronizes the memory module’s responses with the system bus.
As other computer components increased their speed, memory speed also needed to increase. The double data rate, or DDR, was developed, and the previous technology became known as the single data rate or SDR. DDR was both faster and used less energy than SDR. DDR memory transfers data to the processor on both the rising and falling edges of the clock signal. A clock signal is made up of both a downbeat and an upbeat. Using both beats to transfer data makes double data rate memory significantly faster than single data-rate memory, which used only one edge of the clock signal to transfer data.
Memory technology continues to develop. The next generation of memory, DDR2, is faster and uses less energy than the original DDR. DDR3 and DDR4 continued this trend. Each successive generation is faster and uses less energy. Memory standards are controlled by JEDEC, the Joint Electron Device Engineering Council, an independent semiconductor engineering trade organization and standardization body.
Memory must be compatible with the other components in a computer system. Generally, components are created to the highest standard at the time of manufacture, but with the expectation that technology will continue to change. To prevent users from inserting incompatible memory, modules are physically different for each memory technology generation. These physical differences are standard across the memory industry. One of the reasons for industry-wide standardization in memory is that computer makers need to know the electrical parameters and physical shape of the memory that can be installed in their computers. Because the electrical parameters are different for each generation of memory, the physical shape of the memory changes to prevent the wrong memory from being installed in a computer. Computers can use only the generation of memory that they are designed for.
RAM Speed
The numbers that appear after “DDR” and the generation indicator are the data transfer rate per second of the module. Because double data rate transfers data on both the rising and falling edge of the clock cycle, DDR3-800 is measured by using a 400 clock cycle on a 1066 MHz input/output clock. Please note that hertz is a measure of cycles per second, not the measure of the speed of the cycles.
There is also an industry name that indicates the theoretical bandwidth of the module, for example, “PC3-6400”. Bandwidth is calculated by taking the transfers per second and multiplying by eight (DDR3 transfers data on a bus that is 64 bits wide, and because a byte is eight bits, this is eight bytes of data per transfer).
History
In the early 1940s, memory technology often permitted a capacity of a few bytes. The first electronic programmable digital computer, the ENIAC, using thousands of vacuum tubes, could perform simple calculations involving 20 numbers of ten decimal digits stored in the vacuum tubes.
The next significant advance in computer memory came with acoustic delay-line memory, developed by J. Presper Eckert in the early 1940s. Through the construction of a glass tube filled with mercury and plugged at each end with a quartz crystal, delay lines could store bits of information in the form of sound waves propagating through the mercury, with the quartz crystals acting as transducers to read and write bits. Delay-line memory was limited to a capacity of up to a few thousand bits.
Two alternatives to the delay line, the Williams tube, and Selectron tube originated in 1946, both using electron beams in glass tubes as means of storage. Using cathode ray tubes, Fred Williams invented the Williams tube, which was the first random-access computer memory. The Williams tube was able to store more information than the Selectron tube (the Selectron was limited to 256 bits, while the Williams tube could store thousands) and was less expensive. The Williams tube was nevertheless frustratingly sensitive to environmental disturbances.
Efforts began in the late 1940s to find non-volatile memory. Magnetic-core memory allowed for recall of memory after power loss. It was developed by Frederick W. Viehe and An Wang in the late 1940s, and improved by Jay Forrester and Jan A. Rajchman in the early 1950s, before being commercialized with the Whirlwind computer in 1953.[rx] Magnetic-core memory was the dominant form of memory until the development of MOS semiconductor memory in the 1960s.[rx]
The first semiconductor memory was implemented as a flip-flop circuit in the early 1960s using bipolar transistors.[rx] Semiconductor memory made from discrete devices was first shipped by Texas Instruments to the United States Air Force in 1961. The same year, the concept of solid-state memory on an integrated circuit (IC) chip was proposed by applications engineer Bob Norman at Fairchild Semiconductor.[rx] The first bipolar semiconductor memory IC chip was the SP95 introduced by IBM in 1965.[rx] While semiconductor memory offered improved performance over magnetic-core memory, it remain larger and more expensive and did not displace magnetic-core memory until the late 1960s.[rx][rx]
References
Dr. Md. Harun Ar Rashid, MPH, MD, PhD, is a highly respected medical specialist celebrated for his exceptional clinical expertise and unwavering commitment to patient care. With advanced qualifications including MPH, MD, and PhD, he integrates cutting-edge research with a compassionate approach to medicine, ensuring that every patient receives personalized and effective treatment. His extensive training and hands-on experience enable him to diagnose complex conditions accurately and develop innovative treatment strategies tailored to individual needs. In addition to his clinical practice, Dr. Harun Ar Rashid is dedicated to medical education and research, writing and inventory creative thinking, innovative idea, critical care managementing make in his community to outreach, often participating in initiatives that promote health awareness and advance medical knowledge. His career is a testament to the high standards represented by his credentials, and he continues to contribute significantly to his field, driving improvements in both patient outcomes and healthcare practices.
