Z-RAM
Encyclopedia
- Not to be confused with the Linux zRamZRamzRam is an available feature for certain distributions of Linux, that was previously called "compcache". It increases performance by avoiding paging on disk and instead uses a compressed block device in RAM in which paging takes place until it is necessary to use the swap space on the hard disk drive...
feature, previously known as "compcache".
Zero-capacitor (registered trademark, Z-RAM) is a novel DRAM
Dynamic random access memory
Dynamic random-access memory is a type of random-access memory that stores each bit of data in a separate capacitor within an integrated circuit. The capacitor can be either charged or discharged; these two states are taken to represent the two values of a bit, conventionally called 0 and 1...
computer memory
Computer memory
In computing, memory refers to the physical devices used to store programs or data on a temporary or permanent basis for use in a computer or other digital electronic device. The term primary memory is used for the information in physical systems which are fast In computing, memory refers to the...
technology developed by Innovative Silicon based on the floating body effect
Floating body effect
The floating body effect is the effect of dependence of the body potential of a transistor realized by the silicon on insulator technology on the history of its biasing and the carrier recombination processes. The transistor's body forms a capacitor against the insulated substrate...
of silicon on insulator
Silicon on insulator
Silicon on insulator technology refers to the use of a layered silicon-insulator-silicon substrate in place of conventional silicon substrates in semiconductor manufacturing, especially microelectronics, to reduce parasitic device capacitance and thereby improving performance...
(SOI) process technology. Z-RAM has been licensed by Advanced Micro Devices
Advanced Micro Devices
Advanced Micro Devices, Inc. or AMD is an American multinational semiconductor company based in Sunnyvale, California, that develops computer processors and related technologies for commercial and consumer markets...
for possible use in future microprocessor
Microprocessor
A microprocessor incorporates the functions of a computer's central processing unit on a single integrated circuit, or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and...
s. Innovative Silicon claims the technology offers memory access speeds similar to the standard six-transistor SRAM
Static random access memory
Static random-access memory is a type of semiconductor memory where the word static indicates that, unlike dynamic RAM , it does not need to be periodically refreshed, as SRAM uses bistable latching circuitry to store each bit...
cell used in cache memory but uses only a single transistor
Transistor
A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current...
, therefore affording much higher packing densities.
Z-RAM relies on the floating body effect
Floating body effect
The floating body effect is the effect of dependence of the body potential of a transistor realized by the silicon on insulator technology on the history of its biasing and the carrier recombination processes. The transistor's body forms a capacitor against the insulated substrate...
, an artifact of the SOI process technology which places transistors in isolated tubs (the transistor body voltages "float" with respect to the wafer substrate underneath the tubs). The floating body effect causes a variable capacitance
Capacitor
A capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...
to appear between the bottom of the tub and the underlying substrate
Wafer (electronics)
A wafer is a thin slice of semiconductor material, such as a silicon crystal, used in the fabrication of integrated circuits and other microdevices...
, and was a problem that originally bedeviled circuit designs. The same effect, however, allows a DRAM-like cell to be built without adding a separate capacitor, the floating body effect taking the place of the conventional capacitor. Because the capacitor is located under the transistor (instead of adjacent to, or above the transistor as in conventional DRAM
Dram
Dram or DRAM may refer to:As a unit of measure:* Dram , an imperial unit of mass and volume* Armenian dram, a monetary unit* Dirham, a unit of currency in several Arab nationsOther uses:...
s), another connotation of the name "Z-RAM" is that it extends in the negative z-direction.
The reduced cell size leads, in a roundabout way, to Z-RAM being faster than even SRAM if used in large enough blocks. While individual SRAM cells are sensed faster than Z-RAM cells, the significantly smaller cell reduces the size of Z-RAM memory blocks and thus reduces the physical distance that data must transit to exit the memory block. As these metal traces have a fixed delay per unit length independent of memory technology, the shorter lengths of the Z-RAM signal traces can offset the faster SRAM cell access times. For a large cache memory (as typically found in a high performance microprocessor), Z-RAM offers equivalent speed as SRAM but requiring much less space (and thus cost). Response times as low as 3ns have been claimed.
SOI technology is targeted at very high performance computing markets and is relatively expensive compared with more common CMOS technology
CMOS
Complementary metal–oxide–semiconductor is a technology for constructing integrated circuits. CMOS technology is used in microprocessors, microcontrollers, static RAM, and other digital logic circuits...
. Z-RAM offers the hope of cheaper on-chip cache memory, with little or no performance degradation, a compelling proposition if the memory cell can be proven to work in production volumes.
In March 2010, Innovative Silicon announced it was jointly developing a non-SOI version of Z-RAM that could be manufactured on lower cost bulk CMOS technology.http://www.eetimes.com/showArticle.jhtml;jsessionid=HVHQ2BAG2ESOFQE1GHRSKHWATMY32JVN?articleID=223900169
AMD
Advanced Micro Devices
Advanced Micro Devices, Inc. or AMD is an American multinational semiconductor company based in Sunnyvale, California, that develops computer processors and related technologies for commercial and consumer markets...
has licensed the second generation Z-RAM to research it for potential use in their future processors, but is not planning to start using it.
DRAM producer Hynix
Hynix
Hynix Semiconductor Inc. chips and flash memory chips. Founded in 1983, Hynix is the world's second-largest memory chipmaker, the largest being Samsung Electronics. Formerly known as Hyundai Electronics, the company has manufacturing sites in Korea, the U.S., China and Taiwan...
has also licensed Z-RAM for use in DRAM chips.
Innovative Silicon was closed on June 29, 2010. Its officers have left, and its patent portfolio was transferred to Micron Technology
Micron Technology
Micron Technology, Inc. is an American multinational corporation based in Boise, Idaho, USA, best known for producing many forms of semiconductor devices. This includes DRAM, SDRAM, flash memory, SSD and CMOS image sensing chips. Consumers may be more familiar with its consumer brand Crucial...
in December 2010.