CACHE MEMORY, also called CPU memory, is random access memory (RAM) that a computer microprocessor can access more quickly than it can access regular RAM.

As the microprocessor processes data, it looks first in the cache memory and if it finds the data there (from a previous reading of data), it does not have to do the more time-consuming reading of data from larger memory.

Cache memory is fast and it is expensive. It is categorized in levels that describe its closeness and accessibility to the microprocessor. Level 1 (L1) cache, which is extremely fast but relatively small, is located close to the processor. Level 2 (L2) cache is located half-way between the process and the system bus; it is fairly fast and medium-sized. Level 3 (L3) cache is relatively large and close to RAM.

Memory cache can work under three different configurations: direct mapping, fully associative and set associative. With direct mapping each block is mapped to exactly one cache location. With fully associative mapping, each block is mapped to any cache location. With set associative, each block is mapped to a subset of cache locations.

REGISTER

In a computer, a register is one of a small set of data holding places that are part of a computer processor. A register may hold a computer instruction, a storage address, or any kind of data (such as a bit sequence or individual characters). Some instructions specify registers as part of the instruction. For example, an instruction may specify that the contents of two defined registers be added together and then placed in a specified register. A register must be large enough to hold an instruction - for example, in a 32-bit instruction computer, a register must be 32 bits in length. In some computer designs, there are smaller registers - for example, half-registers - for shorter instructions. Depending on the processor design and language rules, registers may be numbered or have arbitrary names.

Read-only memory or ROM is a form of data storage in computers and other electronic devices that cannot be easily altered or reprogrammed. RAM is referred to as volatile memory and is lost when the power is turned off whereas ROM in non-volatile and the contents are retained even after the power is switched off.

Random Access Memory or RAM is a form of data storage that can be accessed randomly at any time, in any order and from any physical location in contrast to other storage devices, such as hard drives, where the physical location of the data determines the time taken to retrieve it. RAM is measured in megabytes and the speed is measured in nanoseconds and RAM chips can read data faster than ROM.

Differences in use

RAM allows the computer to read data quickly and efficiently to be able to run applications efficiently, whereas ROM stores the program required to initially boot the computer and perform diagnostics. RAM is a common type of memory found in computers and printers, and can go up to a few gigabytes. ROM is usually only a few thousand bytes of storage in personal computers. RAM is primary memory and volatile

Different Types of RAM vs ROM

The main types of RAM include static RAM (SRAM), dynamic RAM (DRAM). Static RAM is more expensive and has more capacity for storage than dynamic RAM that has to be refreshed more often, and is thus slower.

ROMs are integrated circuits that contain data and most often cannot be altered. There are some types that can be somewhat modified that include programmable ROM (PROM), erasable programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM) and Flash, which is a type of EEPROM. PROM is a type of ROM that can be programmed only once by a special device and uses high voltages. EPROM can be rewritten using UV radiation, whereas EEPROM can be rewritten electrically and such devices do not require to be removed from the computer. Flash drives are modern version of EEPROM and fastest to erase and rewrite. Some other common types of ROM are CD-ROM, CD-R and CD-RW which is used to store media and music files.

Comparison chart

Platter: These are metal alloy discs that are coated with an aluminum alloy or glass substrate. The traditional material is aluminum alloy but these days, newer hard drives are coated with a glass substrate because it provides greater durability. This is where the hard drive stores information. All your data is stored using magnetic polarity differences.

Areal Density: Areal density is the amount of data that can be packed in a square-inch of space of a platter. Each platter stores information in tracks. You can think of the tracks as circular rings that are etched out the platter - magnetically of course. And in these rings, the data bits are recording linearly. The more bits that are packed along the tracks, the more data can be stored.

Spindle: Each platter is stacked together on top of a spindle. The motor that spins the platters rotate at a specific speed. The most common is 5,400RPM (Rotations per Minute). High-end hard drives that are used in workstations and or servers can spin at 7,200RPM, 10,000RPM or even 15,000RPM. The faster the platters rotate, the faster the read/write head can obtain data - the destination sector arrives under the read/write head faster. The spindle motor uses ball-bearings to rotate around. Using ball bearings produces faster and smoother operation than brush-less motors. The spindle is one of the most sensitive parts of the hard drive. If it receives a significant amount of shock, a bearing may be shot lose from the bearing ring that holds the bearings.

Actuator: The actuator is responsible for moving actuator arms which hold the read/write heads precisely with a specific track and sector. The actuator is one of the most important parts of the hard drive that determine the speed of the drive and how many bits it can pack on its platters. The actuator must align the read/write head precisely, if not, data read and write errors can occur.

 The read/write head is attached to the ends of the actuator arms. It looks like the heads are touching the platters. But in actuality, they are "flying" above the platters using a cushion of air created by the spinning platters. This thin layer of air is what prevents the heads from coming in contact with the platters. The heads are extremely close to the platters. An excessive shock to the drive during operation can mean disastrous outcomes. Also, remember how we mentioned that these components are sealed in a dust-free chassis? If the heads are flying only about 2 microns above the surface of the platter, can you imagine the consequences if any small particle were to come between the head and the platter?

Read\Write Heads: The heads are responsible for writing to the drive and reading from it. They write data by arranging the magnetic particles on the surface of the platters. When arranged in one direction, the particles will produce a northern polarity and when arranged in the other direction, they will produce a southern polarity. When reading from the platters, the head will detect the polarity of the particles and translate that into electrical signals and send the signals back to the on-board hard drive controller. 

Controllers: The hard drive controller is attached on the exterior of the hard drive chassis. It contains DSP (Digital Signal Processors) chips that control dataflow, etc. It also contains cache modules to keep frequently used data close at hand. The mini PCB inside the hard drive itself is the controller for the actuator. 

RAM ROM

Definition

Random Access Memory or RAM is a form of data storage that can be accessed randomly at any time, in any order and from any physical location. Allowing quick access and manipulation.

Read-only memory or ROM is also a form of data storage that cannot be easily altered or reprogrammed. Stores instructions that are not necessary for re-booting up to make the computer operate when it is switched off. They are hardwired.

Stands for

Random Access Memory Read-only memory

UseRAM allows the computer to read data quickly to run applications. It allows reading and writing.

ROM stores the program required to initially boot the computer. It only allows reading.

Volatility

RAM is volatile i.e. its contents are lost when the device is powered off.

It is non-volatile i.e. its contents are retained even when the device is powered off.

TypesThe two main types of RAM are static RAM and dynamic RAM.

The types of ROM include PROM, EPROM and EEPROM.

Magnets: You may think that placing a magnet near a hard drive will destroy the data inside. This is true. But what you may not know is that there are two very strong magnets inside of the drive. The magnets are located inside the actuator. One is on top of the actuator arms and the other one is underneath. The reason why these magnets do not affect the platters is that the magnetic field on the magnets lie on a vertical axis. If they were on a horizontal axis, the field would stretch onto the platters, destroying the data. Another reason is that the magnetic signals recorded on the platters aren't any regular magnetic fields but they are electro-magnetically recorded. Electro-magnets are many times more stronger than natural magnets.

FLOPPY DISK

FLOPPY DRIVE

INSIDE A FLASH DRIVE

The flash drive looks small and compact. Yet it is able to store an incredibly huge amount of information. The video below shows the three basic components of a flash drive:

1. The board holds all of the internal components and includes the USB connector. The flash drive uses the board as a means of transferring power and data to and from the USB.

2. The NAND Flash memory storage chip is the place where all our files are stored.

3. The controller chip is the ‘brain’ of the flash drive.

Retrieves information from the drive and

Reading/recording information on the NAND flash memory storage chip.

1. USB Connector: USB (Universal Serial Bus) acts as an interface between the NAND flash memory chip and the computer the flash drive is plugged into.

2. USB mass storage controller (or the controller chip): explanation above

3. Test points: These are electrical pins that serve only as electrical contact points. They are primarily used to electrically stimulate and exercise the flash drive during the assembly process – serving as a means of identifying any defects on the board. Think of it as a cost-effective way of Quality Control.

4. NAND flash memory chip: explanation above

5. Crystal Oscillator: It is a piece of quartz crystal designed to vibrate at a very particular frequency. It is used as a digital “clock”.

6. LED indicator light: Used to indicate if the flash drive is working and functioning

7. Write-protect switch: An optional component used to safeguard the information saved on the flash drive.

8. Space to put a second NAND flash memory chip: An additional slot for manufacturers to put another memory chip which can increase the storage capacity