What is meant by Random Access?

Random access is generally known as direct access. Random access is the capability to have access to any item from a given population of elements at random. Sequential access is the direct opposite of random access. In random access, the elements can be retrieved irrespective of the location. In order to move from point A to Z,  you can just jump to point Z in random access system. The disk is an example of random access.

Random vs Sequential Access

The random-access files allow the user to write and read data anywhere in the file, whereas, in sequential access files the user can write and read files sequentially (from the beginning). Sequential access has advantages when you access information in the same order all the time and also faster compared to random access. Random access file has the advantage that you can search through them and find the data you need more easily.

The old-fashioned tap drive is a sequential drive and also an example of sequential access. It is no longer used in modern computers but still, some companies use tap drive to create a durable backup archive.

A hard disk is a random access device and non-volatile storage for digital data. The data on hard disks are accessed randomly, that is, it can retrieve and store data in any order. Hard disk is an example of random access.

Memory devices                                                              

Memory is used to store the instructions and data. In computers, the storage space is known as computer memory. Required instructions and data are stored in this memory space. The computer memory will be classified into small parts, where every part is known as a cell. There will be a unique address for every cell or location. Memory is classified into two kinds and they are,

• External memory
• Internal memory

External memory

External memory refers to the storage, where the data is stored or retained persistently. This memory can be either removable storage or an embedded device. This memory is also known as secondary memory. USB flash drives, compact discs, and hard disks are some external memory devices.

Internal memory

Internal memory refers to memory, where small data is stored and can access the data quickly. This memory is also known as main/primary memory. It is classified into random-access memory (RAM) and read-only memory (ROM).

(a) Random-access memory

Random-access memory is the abbreviation of RAM. RAM can access the files and data randomly from the cache memory. It is the hardware of the computer and embedded on the motherboard. The data stored in RAM will be lost when there is no powers supply to the laptop or pc. The Basic Input Output System (BIOS) is used to check the stored information in RAM. The other names of RAM are primary memory, internal memory, main memory, and volatile memory.

Major types of RAM

The two major classifications of random-access memory are:

• Static RAM: Static Random-access memory is the abbreviation of SRAM. SRAM can retain the data in static form till the supply of power is turned off. Compared to dynamic RAM, this consumes more power and is quite expensive. Flip-flop is used to store the data in SRAM. The data in SRAM is stored using four to six transistors in the memory cell and used as cache memory to the processor. Non-volatile SRAM and pseudo SRAM are the various kinds of SRAM. The Non-volatile SRAM will store the information when there is no power supply and pseudo SRAM use a self-refresh circuit.

• Dynamic RAM: Dynamic Random-access memory is the abbreviation of DRAM. Dynamic RAM reduces the power consumption by using a separate capacitor to store every data bit within the integrated circuit. Compared to SRAM, the access time is high in DRAM. Dynamic RAM is a kind of semiconductor memory that is designed to store program files and data; however, the computer processor needs the files and data to perform their functions. The packaging density is high in Dynamic Random-access memory. Synchronous DRAM (SDRAM), Double Data Rate SDRAM (DDR), Rambus DRAM (RDRAM), and memory module formats are the four kinds of Dynamic RAM. Single In-line Memory Module (SIMM), Rambus In-line Memory Module (RIMM), and Double In-line Memory Module (DIMM) are the three kinds of memory module package is dynamic RAM. 

Types of Random Access Memory devices

• Fast Page Mode Dynamic Random-Access Memory (FPM DRAM) is a kind of RAM that waits through the entire process of locating a bit of data by columns and rows and then reading the bit before it begins on the next bit. The maximum transfer rate is around 176 Mbps.
• VRAM (video) is the optimized RAM for the video adapter. The chips in VRAM contain two ports, the video data is written to the chips and simultaneously video adapter reads the memory in order to refresh the current display.
• Flash memory is an electrically erasable memory. Single transistor memory is used to store the bit in the flash memory. It helps in cost reduction and power consumption is low. MP3 players, digital cameras, and so forth use flash memory.

(b) Read-only memory

Read-only memory is the abbreviation of ROM. Using ROM, the user can only read and cannot write in the memory. Generally, ROM is non-volatile and the data is stored permanently. The instruction stored in ROM is used to start the system when the system gets turned on and this operation is known as bootstrap.

Types of ROM

• Masked ROM (MROM) is a hard-wired device that contains pre-defined data or instructions.
• Programmable Read-Only Memory (PROM) is a memory where the user can modify the data only once.
• Erasable Programmable Read-Only Memory (EPROM) is used to erase by exposing it to ultra-violet lights.
• Electrically Erasable Programmable Read-Only Memory (EPROM) is erased electrically and can be reprogramed up to 10000 times.

Context and Applications

This topic is important for postgraduate and undergraduate courses, particularly for,

• Bachelors in computer science engineering
• Associate of science in computer science

Practice Problems

Question 1: Which memory is difficult to interface with the processor?

1. Random-access memory
2. Dynamic Random access memory
3. Direct access memory
4. External memory

Answer: Option b is correct.

Explanation: DRAM stores each bit of data in a separate capacitor. The electric charge on the capacitors slowly leaks off, so the data on the chip would be lost. To prevent them, DRAM refreshes periodically so due to refreshment it is quite difficult to interface with the CPU.

Question 2: Both EPROM and ____ are the types of random access memory.

1. SRAM
2. EEPROM
3. Cache memory
4. DRAM

Answer: Option b is correct.

Explanation: EPROM and EEPROM are the types of ROM. The data in ROM can be accessed randomly and hence both EEPROM and EPROM are random access memory.

Question 3: RAM is classified into __ types.

1. 3
2. 4
3. 2
4. 5

Answer: Option c is correct.

Explanation: RAM is classified into Static RAM (SRAM) and Dynamic RAM (DRAM). When comparing the access time SRAM will be faster than DRAM. SRAM is expensive and power-consuming. DRAM is used to store files and data.

Question 4: Select the memory modular package in DRAM.

1. Computer memory
2. Memory cell
3. Spin-transfer
4. SIMM

Answer: Option d is correct.

Explanation: Double In-line Memory Module (DIMM), Single In-line Memory Module (SIMM), and Rambus In-line Memory Module (RIMM) are the three kinds of memory module package is dynamic RAM. 

Question 5: SRAM is used as ____.

1. Catch memory
2. Virtual memory
3. Primary memory
4. Memory cell

Answer: Option a is correct.

Explanation: Cache memory is used by SRAM to process data. The non-volatile SRAM will store the information when there is no power supply.