Computer Memory Part 2: SRAM, ROM, and Flash

Computer Memory Part 2: SRAM, ROM, and Flash


This is a continuation on Computer Memory Part 1. To keep up with the changing environment of the memory market, Advanced MP Technology ensures that our procurement professionals have an in-depth product knowledge.


In this blog we will discuss the importance of SRAM, flash, and ROMs.


SRAM (Static Random Access Memory)

What is it?  DRAM uses a single transistor to store each bit, which causes a need to refresh for the charge to remain. Unlike the DRAM, SRAM use a pair of transistors in a flip-flop or seesaw motion to maintain the charge. This eliminates the time consuming need to refresh, which makes SRAM considerably faster but limits its density or capacity potential.


Types of SRAM: - Basic or Slow SRAM: 150ns-40ns. Up to 16Mb of information - Cache RAM or Fast SRAM: 35ns-10ns. Up to 16Mb of information - Synchronous SRAM: 7ns- 2 ns. Up to 72Mb of information


Major Manufacturers: Cypress, IDT, ISSI/ICSI, Renesas Technology, and Alliance Semiconductor


News of Today:  The development in the SRAM industry revolves around making an advanced low power part that can hold more memory and have a limited number of soft errors. Renesas Electronics has recently introduced a 16 and 32 megabit advanced low power SRAM with over 500 times the resistance to soft errors compared to the full CMOS memory. These parts are designed to provide an enhanced reliability and longer backup battery life for applications such as factory automation, industrial equipment, and the smart grid.


ROMs

What is it?  These differ in technology from RAM products (DRAM/SRAM) as the data is programmed onto the chip, so it is retained even when power is not there. Similar to a CD or DVD, these are classified as non-volatile memory.


Types of ROMs: - PROMs: Programmable Read Only Memory (Becoming obsolete) - EPROMs: Erasable Programmable Read Only Memory       – Plastic DIP EPROMs: One time programmable, cannot be erased.       – Ceramic DIP EPROMs: Has a glass window, which allows the programmer to erase and reprogram the device by using UV light - EEPROMs: Electrically Erasable Programmable Read Only Memory. The main ROM that is still around.


Major Manufacturers: - EPROM: Atmel, Macronix, and ST-Microelectronics - EEPROM: ST-Microelectronics, Numonics, Micron, and Atmel

News of Today:  EEPROMs exist in almost all IoTs, therefore many manufacturers are targeting these devises when designing new ROMs. Atmel has recently introduced a two pin self powered serial EEPROM that targets the IoT, battery, consumable, and cable identification markets. The two pins are used as a data pin and a ground pin for operations; this makes it ideal for IoTs and wearable devices. Since the part is self-powered, there is no need for a power source or Vcc pin. Additionally, the new devices have an ultra-high write endurance capability that allows more than one million cycles for each memory location. This meets the requirements for today’s high-write endurance applications.


Flash

What is it?   EPROMs need to be completely erased for re-programming but, Flash can be erased in sectors or blocks.


Types of Flash: - NOR: Introduced in 1988 by Intel. NOR flash offers eXecute In Place (XIP) programming capabilities and high read performance. It is also merely cost-effective in low densities (1Mb-16Mb) and suffers from extremely low and slow write/erase performance. NOR Flash is used mainly in home appliances, embedded designs, and low end set top boxes.

- NAND: Introduced in 1989 by Toshiba. NAND flash utilizes a memory cell that is 40% smaller than NOR Flash, while offering extremely high densities (low cost-to-bit pricing) and faster write and erase rates. NAND Flash is used mainly in PC cards, compact flash, SD cards, USBs, SSDs, and MP3 players.


Major Manufacturers: - NOR Flash: Intel, AMD, Numonyx, Micron, ST-Microelectronics, and Atmel - NAND Flash: Intel, Micron, Toshiba, and Samsung


News of Today:  Samsung has recently introduced the world’s first 48-layer, three-dimensional, vertical NAND flash memory chip. This will allow Samsung to make SSDs (Solid State Drives) and other flash-based devices more affordable while increasing their market share. The three-dimension NAND flash stacks layers of data-storing silicon like a microscopic skyscraper, which creates a new pathway for the non-volatile memory market. This new flash innovation also allowed Samsung to develop a 15TB SSD drive, which is the densest SSD created to date.


Advanced MP Technology is a worldwide trusted distributor for electronic components. We have been supporting our customers fro over 37 years with their requirements for memory commodities.